11th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions

26.03.2023, 06:50 → 31.03.2023, 19:00 Europe/Berlin

Stadthalle (Aschaffenburg)

Anton Andronic (IKP, WWU), Christian Klein-Bösing, Ralf Averbeck (GSI Helmholtzzentrum für Schwerionenforschung GmbH), Silvia Masciocchi (GSI - Helmholtzzentrum fur Schwerionenforschung GmbH (DE))

The 11th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions took place in Aschaffenburg (Germany) from 26th March until 31st March 2023.

The student lectures took place on Sunday, March 26th at GSI/FAIR Darmstadt.

Conference photo

The conference is focused on experimental and theoretical developments on perturbative probes of hot and dense QCD matter as studied in high-energy nucleus-nucleus, proton-nucleus and proton-proton collisions. Specifically, topics for discussion will include:

• Jets and their modification in QCD matter
• High momentum hadrons and correlations
• Heavy quarks and quarkonia
• Electromagnetic and electroweak probes
• Early time dynamics and nuclear PDFs
• Future experimental facilities

The conference is in-person only.

Statement on the Russian war on Ukraine

The organizers of HP2023 strongly condemn the war that Russia conducts against Ukraine.
We subscribe to the statements on the war by the European Organisation for Nuclear Research (CERN), the European Physical Society (EPS), the German Physical Society (DPG), and the German Research Council (DFG).
 

Conference logo.

2023_HP_Data_Protection.pdf

Flyer Outreach

HP2023-Poster.pdf

HP23_logo_s.png

HP23_photo.jpeg

Poster öffentlicher Vortrag

Poster Urknall Unterwegs

Sonntag, 26. März

08:30 → 09:35 Bus from Aschaffenburg

Meet at bus stop in Aschaffenburg

09:35 → 09:50 Arrival at GSI & Registration

09:50 → 11:00 Student Lectures

09:50 Welcome from the LOC chairs

Sprecher: Chairs

10:00 From high-momentum hadrons and correlations to jets

Sprecher: Jana Bielcikova

hp2023-students-jb-final.pdf

hp2023-students-jb-final.pptx

11:00 → 11:25 Coffee break

11:25 → 13:05 Student Lectures: FAIR Construction Site Visit

11:25 FAIR Platform Visit (Groups C+D)

Sprecher: Patrick Dahm (GSI), Tetyana Galatyuk

11:25 Introduction to GSI/FAIR + Q&A (Groups A+B)

Sprecher: Frank Herfurth (GSI)

12:15 FAIR Platform Visit (Groups A+B)

Sprecher: Patrick Dahm (GSI), Tetyana Galatyuk

12:15 Introduction to GSI/FAIR + Q&A (Groups C+D)

Sprecher: Frank Herfurth (GSI)

13:05 → 14:30 Lunch

14:30 → 15:30 Student Lectures

14:30 Future experimental facilities and detectors

Sprecher: Luciano Musa

Musa_HP_MAR_2023.pdf

15:30 → 16:00 Coffee break

16:00 → 18:00 Student Lectures

16:00 Theory of hard processes in heavy-ion collisions

Sprecher: Prof. Carlos Salgado (IGFAE)

HP2023-CAS.pdf

17:00 Heavy flavours and quarkonia

Sprecher: Andrea Dainese (INFN Padova)

Dainese_HPlecture_Mar2023.pdf

18:00 → 19:00 Bus from GSI to Aschaffenburg

Montag, 27. März

08:00 → 09:00 Registration

09:00 → 10:40 Plenary Session I

Sitzungsleiter: Barbara Jacak

09:00 Welcome Address

Sprecher: Paolo Giubellino, Chairs

09:15 ALICE Experimental Highlights

Sprecher: James Mulligan (Lawrence Berkeley National Laboratory)

ALICE_Highlights_Mulligan.pdf

09:50 ATLAS Experimental Highlights

Sprecher: Petr Balek (AGH Krakow)

PetrBalek_ATLASHighlights.pdf

10:15 CMS Experimental Highlights

Sprecher: Georgios Krintiras (The University of Kansas)

HP23_CMS_Plenary_GKK.pdf

10:40 → 11:10 Coffee Break

11:10 → 12:30 Plenary Session II

Sitzungsleiter: Christina Markert (University of Texas at Austin (US))

11:10 LHCb Experimental Highlights

Sprecher: Jiayin Sun (INFN Cagliari)

lhcb_hp23_sun_v3.pdf

11:30 PHENIX Experimental Highlights

Sprecher: Gabor David (Stony Brook University)

hp2023_david_overview.pdf

11:50 STAR Experimental Highlights

Sprecher: Joern Putschke, Nihar Sahoo (Shandong University)

STAR_Highlights_Sahoo.pdf

12:10 HADES Experimental Highlights

Sprecher: Szymon Harabasz (Technische Universität Darmstadt)

SzymonHarabasz_HP2023_ver4_copy.pdf

12:30 → 14:00 Lunch Break

14:00 → 16:05 Plenary Session III

Sitzungsleiter: Ramona Vogt

14:00 Early time dynamics and constraints on medium evolution

Sprecher: Kirill Boguslavski

Boguslavski_HardProbes2023.pdf

14:25 Electroweak probes: Theory

Sprecher: Jean-Francois Paquet (Vanderbilt University)

jfpaquet_em_probes_theory_hp2023.pdf

14:50 Electroweak probes: Experiment

Sprecher: Austin Baty (Rice University)

Baty_EWKProbes_HP20203_v6.pdf

15:15 Open heavy flavors: Theory

Sprecher: Santosh Kumar Das (IIT Goa)

Das_HF_HP2023.pdf

15:40 Open heavy flavors: Experiment

Sprecher: Zaida Conesa del Valle (IJCLab (CNRS/IN2P3, Université Paris-Saclay, Université Paris-Cité))

HP23_HF_ZConesadelValle.pdf

16:05 → 16:40 Coffee Break

16:40 → 18:20 Plenary Session IV

Sitzungsleiter: Jana Bielcikova

16:40 Jets medium modifications

Sprecher: Carlota Andres (CPHT, École polytechnique)

andresc_HP2023.pdf

17:05 Jets substructure

Sprecher: Alba Soto Ontoso

hp_alba.pdf

17:30 Jet-induced medium response

Sprecher: Yeonju Go (University of Colorado Boulder)

HP2023_jet_medium_response_yeonju.pdf

17:55 Monte Carlo modeling of jets

Sprecher: Liliana Apolinário (LIP)

LApolinario_HP23.pdf

19:30 → 21:00 Welcome Reception

at the Restaurant Jedermann im Stadttheater
Schloßgasse 8, 63739 Aschaffenburg

Dienstag, 28. März

09:00 → 10:20 Parallel: Early-Time Dynamics & nPDFs

Sitzungsleiter: Matthias Kaminski (University of Alabama)

09:00 New constraints on nucleon structure from LHCb

The forward geometry of the LHCb detector provides unprecedented access to both the very high and very low regions of Bjorken $x$ inside the nucleon. With full particle ID and a fast DAQ, LHCb is able to fully reconstruct plentiful charged particles and $\pi^{0}$ mesons, as well as relatively rare probes such as $Z$ bosons and heavy quarks, providing a unique set of constraints on nucleon structure functions. This talk will discuss recent LHCb measurements sensitive to intrinsic charm within the proton, modification of parton distribution functions inside the nucleus, and show the impact of recent LHCb measurements that dramatically reduce nPDF uncertainties at low $x$.

Sprecher: Sara sellam (University of Santiago de Compostela)

HP2023_sara_sellam.pdf

09:20 Early time dynamics of QCD with conserved charges in heavy-ion collisions

In the early stages of heavy-ion collisions, at the highest energies, the system begins in a highly anisotropic state which is far from equilibrium. At later times, the dynamic evolution of the system is well described in the framework of relativistic hydrodynamics which requires local thermodynamic equilibrium. The KoMPoST framework has had some success in bridging the gap between these descriptions via a coarse-grained, non-equilibrium evolution of the system assuming a medium dominated completely by gluons. In this work, we present new results in this framework which include quark degrees of freedom in the response of the system to perturbations from the non-equilibrium background.

Sprecher: Travis Dore (Universität Bielefeld)

HP23_dore.pdf

09:40 Condensation and early time dynamics in QCD plasmas

High energy nuclear collisions produce far-from-equilibrium matter with a high density of gluons at early times. We identify for the first time two local order parameters for condensation, which can occur as a consequence of the large density of gluons. We demonstrate that an initial over-occupation of gluons can lead to the formation of a macroscopic zero mode towards low momenta that scales proportionally with the volume of the system—this defines a gauge invariant condensate. The formation of a condensate at early times has intriguing implications for early time dynamics in heavy ion collisions.

Sprecher: Lillian de Bruin (ITP, Universität Heidelberg)

LdeBruin_HardProbesTawk.pdf

10:00 System size dependence of pre-equilibrium and applicability of hydrodynamics in heavy-ion collisions

Within a microscopic kinetic description based on the Boltzmann equation, we evaluate the importance of the pre-equilibrium stage in high-energy heavy-ion collisions for final state observables over a large range of viscosity and system size. We use our results to determine the range of applicability of an effective description in relativistic viscous hydrodynamics. We find that hydrodynamics provides a quantitatively accurate description of collective flow when the average inverse Reynolds number is sufficiently small and the early pre-equilibrium stage is properly accounted for. We discuss different possible treatments of the pre-equilibrium phase in kinetic theory, KoMPoST and hydrodynamics and assess their applicability.

Sprecher: Clemens Werthmann (Universität Bielefeld)

Hard_Probes_2023-Werthmann.pdf

09:00 → 10:20 Parallel: Heavy Flavours & Quarkonia

Sitzungsleiter: Olaf Kaczmarek

09:00 Open heavy flavor production in $p$Pb and PbPb collisions at LHCb

Heavy quarks are produced in the early stage of heavy ion collisions due to their large mass, and experience the entire evolution of the QCD medium. The baryon-to-meson ratio, in particular, the $\Lambda_c^+$/$D^0$ ratio, provides valuable information on charm hadronization mechanisms, testing the role of coalescence in the Quark-Gluon Plasma created in PbPb collisions. In $p$Pb collisions, heavy quarks are essential to study cold nuclear matter effects, which include the modification of nuclear parton distribution functions, energy loss in the nucleus, and other effects, providing a crucial baseline for interpreting PbPb measurements. In this talk, the first LHCb open charm measurement in PbPb collisions, the $\Lambda_c^+$/$D^0$ ratio, will be presented. Moreover, this presentation will show precision measurements of open charm production from a rich set of charmed hadrons in $p$Pb collisions at 5.02 and 8.16 TeV, including the first measurement of $\Xi_c^+$ baryons in heavy ion collisions. The nuclear modification factor $R_{p\mathrm{Pb}}$, forward-backward ratio $R_{\mathrm{FB}}$ and particle production ratios of charm baryons and mesons will be discussed and compared to models.

Sprecher: Roman Litvinov (INFN Cagliari)

RLitvinov_hp23.pdf

09:20 Higher orders in opacity in QGP tomography

We consider the problem of including a finite number of scattering centers in dynamical energy loss and classical DGLV formalism. Previously, either one or an infinite number of scattering centers were considered in energy loss calculations, while attempts to relax such approximations were largely inconclusive or incomplete. In reality, however, the number of scattering centers is 4-5 at RHIC and the LHC, making the above approximations inadequate and this theoretical problem important for QGP tomography.

We derived explicit analytical expressions for dynamical energy loss and DGLV up to the 4th order in opacity, resulting in complex mathematical expressions that were, to our knowledge, obtained for the first time. These expressions were then implemented into an appropriately generalized DREENA framework to calculate the effects of higher orders in opacity on a wide range of high-pt light and heavy flavor predictions. Results of extensive numerical analysis, including their intuitive interpretations, will be presented.

Sprecher: Magdalena Djordjevic

HP2023_MagdalenaDjordjevic.pdf

09:40 Intrinsic Charm Production in Fixed-Target Experiments at the LHC

A nonperturbative charm production contribution, known as intrinsic charm, has long been speculated. While it has yet to be satisfactorily proven, there have been recent tantalizing hints. Several experiments, either taking data or
planned, could proivde definitive evidence in the next few years. Experiments that have taken $J/\psi$ and $D$ meson data include SeaQuest at Fermilab and SMOG at LHCb, see Refs. [1,2] and references therein. Future experiments such as NA60+ are in an energy regime where the intrinsic charm quark signature could be large and unmistakeable, as discussed in recent work [3]. These predictions are discussed and compared to previous fixed-target data.

R. Vogt, Limits on Intrinsic Charm Production from the SeaQuest Experiment, Phys. Rev. C 103 (2021), 035204.

R. Vogt, Contribution from Intrinsic Charm Production to Fixed-Target Interactions at the LHC, to be submitted.

R. Vogt, Energy dependence of intrinsic charm production: Determining the best energy for observation, Phys. Rev. C 106 (2022) 025201.

This work was performed under the auspices of the U.S.\ DoE by LLNL under Contract DE-AC52-07NA27344 and supported by LDRD projects 21-LW-034 and 23-LW-036.

Sprecher: Ramona Vogt (LLNL and UC Davis)

HP23_talk.pdf

10:00 Radiative energy loss of heavy quark through soft gluon emission in QGP

The Low's theorem is applied to the soft gluon emission from heavy quark scattering in quark-gluon plasma (QGP). The QGP is described by the DQPM (Dynamical QuasiParticle Model) which reproduces the EoS from lQCD at finite temperature and chemical potential. We show that if the emitted gluon is soft and of long wavelength, the scattering amplitude can be factorized into the scattering part and the emission part and the Slavnov-Taylor identities are satisfied in the leading order. Imposing a proper upper limit on the emitted gluon energy, we obtain the scattering cross sections of charm quark as well as the transport coefficients (momentum drag and diffusion) in the QGP with and without gluon emission.

Sprecher: Taesoo Song (GSI)

2023HP-song.pdf

09:00 → 10:20 Parallel: High-Momentum Hadrons & Correlations

Sitzungsleiter: Jamie Nagle (University of Colorado Boulder)

09:00 Looking for collective origin of strangeness enhancement in small collisions systems with ALICE at the LHC

The main goal of the ALICE experiment is to study the physics of strongly interacting matter, including the properties of the quark-gluon plasma (QGP). The increase of relative production of strange hadrons with respect to non-strange hadrons is historically considered as one of the signatures of QGP formation during the evolution of the system created in heavy-ion collisions. Recent measurements performed in high-multiplicity proton-proton (pp) and proton-lead (p-Pb) collisions have shown features that are reminiscent of those observed in lead-lead (Pb-Pb) collisions. The microscopic origin of this phenomenon is still not fully understood: is it related to soft particle production or to hard scattering events, such as jets? To separate strange hadrons produced in jets from those produced in soft processes, the angular correlation between high-$p_\rm{T}$ charged particles and strange hadrons has been exploited. The near-side jet yield and the out-of-jet yield of $K^0_S$, $\Xi$, and $\phi$ have been studied as a function of the multiplicity of charged particles produced in pp collisions at $\sqrt{s}$ = 13 TeV and p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV. New results suggest that out-of-jet processes are the dominant contribution to strange particle production. The results of these measurements are compared to expectations from state-of-the-art phenomenological models implemented in commonly used Monte Carlo event generators.

Sprecher: Ishaan Ahuja

2023-03-26-Ahuja_HP2023_260323_v4.pdf

09:20 Charged-particle production in different collision systems up to very high transverse momentum measured with ALICE

The ALICE experiment at the Large Hadron Collider (LHC) is designed to investigate the properties of the quark-gluon plasma created in high-energy heavy-ion collisions. During the successful data-taking campaigns of LHC Run 1 and Run 2 (2009 - 2018), it recorded data for a variety of collision systems and different center-of-mass energies. As particle production at the LHC is driven by a complex interplay of soft and hard QCD processes, finding a consistent model description for all collision systems is challenging. The study of charged-particle production as a function of multiplicity plays a key role in understanding the properties of the matter created in small (pp, p-Pb) and large (AA) collision systems. The precise tracking capabilities from low to high transverse momentum of the ALICE apparatus give the unique opportunity to measure the evolution of multiplicity-dependent spectral shapes across collision system sizes and energies.

In this contribution, a comprehensive overview of charged-particle production measurements in pp, p-Pb, and AA collisions up to high transverse momentum will be presented. It is obtained by means of a two-dimensional unfolding approach that allows for a detailed correction of detector resolution effects and yields the spectral properties in high-granular multiplicity intervals, maximizing the measurement precision. The results will then be tested against the main theoretical models implemented in commonly used Monte Carlo event generators.

Sprecher: Mario Krüger (Institut für Kernphysik Frankfurt)

2023-03-26-HardProbes2023.pdf

09:40 3D structure of jet-induced diffusion wake in an expanding quark-gluon plasma

Diffusion wake accompanying the jet-induced Mach-cone provides a unique probe of the properties of quark-gluon plasma in high-energy heavy-ion collisions. It can be characterized by a depletion of soft hadrons in the opposite direction of the propagating jet. We explore the 3D structure of the diffusion wake induced by γ triggered jets in Pb+Pb collisions at the LHC energy within the coupled linear Boltzmann transport and hydro model. We identify a valley structure caused by the diffusion wake on top of a ridge from the initial multiple parton interaction (MPI) in jet-hadron correlation as a function of rapidity and azimuthal angle. This leads to a double-peak structure in the rapidity distribution of soft hadrons in the opposite direction of the jets as an unambiguous signal of the diffusion wake. Using a two-Gaussian fit, we extract the diffusion wake and MPI contributions to the double peak. The diffusion wake valley is found to deepen with the jet energy loss as characterized by the γ-jet asymmetry. Its sensitivity to the equation of state and shear viscosity is also studied.

Sprecher: Zhong Yang

HardProbe-2023.pdf

10:00 ATLAS measurement of the two-particle correlation sensitivity to jets in $pp$ collisions

Measurements of two-particle correlations in $pp$ collisions show the presence of long-range correlations along $\Delta\eta$ that are strikingly similar to those seen in heavy-ion collisions. The similarity between the $pp$ and heavy-ion measurements raises the possibility that a tiny droplet of the QGP is produced even in $pp$ collisions. However, models that attribute the correlation in $pp$ collisions to semi-hard processes, can qualitatively reproduce the measurements. Performing the $pp$ measurements while distinguishing between the particles from semi-hard processes, such as low-$p_{\mathrm{T}}$ jets, and the particles produced from soft interactions, can differentiate between these two origins of the $pp$ ridge. This talk presents measurements of two-particle correlations in $pp$ collisions at $\sqrt{s}=13$ TeV with two different particle-pair selections. In the first case, tracks associated with jets are excluded from the correlation analysis. This is shown to affect the magnitude of long-range correlations by only a few percent. New measurements of two-particle correlations, measured between tracks that are constituents of jets and tracks from the underlying event are also presented. These measurements can further elucidate the origin of the $pp$ ridge.

Sprecher: Brian Cole (Columbia University)

Jet2PC_HP2023-March2023_v5.pdf

09:00 → 10:20 Parallel: Jets and their modification in QCD Matter

Sitzungsleiter: Steffen A. Bass

09:00 Measurement of the $R$ dependence of jet quenching in pp and Pb-Pb collisions with ALICE

Jets are excellent probes for studying the deconfined matter formed in heavy ion collisions. Measurements of jet yield and substructure as a function of jet resolution parameter $R$ over a wide range in jet $p_{\mathrm{T}}$ probe the mechanisms underlying the interaction between jets and the QGP, notably the role of opening angle of the hardest jet shower components, and of the angular distribution of medium-induced radiation. In this talk, we will present two measurements of the nuclear modification factor $R_{AA}$ in central Pb-Pb collisions at $\sqrt{s}= 5.02$ TeV with ALICE, addressing the influence of the large uncorrelated background with novel techniques in machine learning and mixed event subtraction. The mixed-event technique, newly introduced in ALICE, enables inclusive jet measurements at low $p_{\mathrm{T}}$ with minimal bias, in a previously unexplored energy regime at the LHC. In addition, the machine learning method enables the measurement of the $R$-dependence of jet suppression for $R=0.6$ down to 40 GeV/c. Finally, we introduce a new infrared and collinear safe measurement of the jet energy flow within jets reconstructed with different resolution parameters $R$. Investigating how the energy is distributed for the same jet with different $R$ allows energy loss to be explored on a jet-by-jet basis instead of between different populations of jets as in inclusive measurements. These results are compared to jet quenching models.

Sprecher: Christos Pliatskas

Quenching_R_dependence_Christos_Pliatskas.pdf

09:20 $R$-dependence of jet observables with JEWEL+v-USPhydro

The $R$-dependence of jet observables provides a new tool in understanding the interplay between the jet energy-loss mechanism and medium response in heavy-ion collisions. We have coupled the Monte Carlo event generators JEWEL and PYTHIA, with initial conditions from the $\rm T_RENTo$ and the state-of-the-art (2+1)D v-USPhydro, for the simulation of jet quenching phenomena in a more realistic medium formed in lead-lead collisions at LHC energy scales.

In this work, we present one of the first studies of the jet nuclear modification $R_{AA}$ and anisotropic flow coefficients $v_{n=2,3}$ as a function of the jet cone radius $R$, in the context of anti-$k_T$ jets, in addition to jet shape observables. The calculations indicate the impacts of the hydrodynamic evolution and weakly-coupled medium response, given by recoils, on the distributions. Results are compared to experimental data in a wide range of jet $p_T$ and collision centrality, and displayed along with large jets ($R \ge 0.6$) predictions.

Sprecher: Herr Leonardo Barreto de Oliveira Campos (University of São Paulo (USP))

hardprobes.pdf

09:40 Novel measurements of dijet quenching with ATLAS

High-energy partons are well established to lose energy when traversing the hot and dense medium produced in heavy-ion collisions. This results in a modification to the transverse momentum distributions of jets, producing a phenomenon known as jet quenching. It has been previously established in Pb+Pb collisions at $\sqrt{s_\textrm{NN}}~=~2.76$~TeV that jet quenching leads to significant modifications to the transverse momentum balance of dijet pairs. More differential measurements are needed to better understand the observed phenomenon. In this talk, we report new, fully unfolded measurements of the dijet momentum balance in Pb+Pb and $pp$ collisions at $\sqrt{s_\textrm{NN}}~=~5.02$~TeV as well as in Xe+Xe collisions at $\sqrt{s_\textrm{NN}}~=~5.44$~TeV. These measurements expand upon previous publications, including the per-event yield of dijets as a function of the momentum balance, which provides insight into the nature of jet quenching. This talk will additionally present a new observable, the d??et pair nuclear modification factors projected along leading and subleading jet transverse momentum, which provides a precise quantification of asymmetric energy loss experienced by dijets.

Sprecher: Martin Krivos (Charles University)

Novel measurements of dijet quenching with ATLAS_Krivos.pdf

10:00 The gradient tomography of dijet in heavy-ion collisions

Jet energy loss and transverse momentum broadening are twin consequences of a jet interacting with a hot and dense QCD matter in heavy-ion collisions. The underlying interaction can be represented by jet transport coefficient $\hat{q}$ distributed in the whole phase space of the bulk medium. The gradient of $\hat{q}$ perpendicular to the momentum direction of an energetic parton leads to an asymmetry of the transverse momentum distribution, which can be used for the initial jet production localization. We investigate such an asymmetry caused by the subleading jet by triggering the leading jet propagating in-plane in Pb+Pb 0-10% collisions at $\sqrt{s} = 5.02$ TeV. Simulations are performed in the linear Boltzmann transport model with fluctuating event-by-event 3+1D viscous hydrodynamic backgrounds. We find that the initial jet production vertex can be localized by combining the dijet transverse imbalance $x_{J} = p^\mathrm{subleading}_{T} / p^\mathrm{leading}_{T}$ and subleading jet transverse gradient asymmetry for different leading jet $p_{T}$ regions. The correlation between both quantities is also investigated to illustrate the properties of $\hat{q}$.

Sprecher: Xin-Nian Wang (LBNL)

hp2023-xnwang3.pdf

hp2023-xnwang3.pptx

hp2023-xnwang4.pdf

hp2023-xnwang4.pptx

10:20 → 10:50 Coffee break

10:50 → 12:30 Parallel: Early-Time Dynamics & nPDFs

Sitzungsleiter: Gojko Vujanovic

10:50 Quarkonia Production in Ultraperipheral PbPb collisions at LHCb

Measurements of quarkonia production in peripheral and ultra-peripheral heavy-ion collisions are sensitive to photon-photon and photon-nucleus interactions, the partonic structure of nuclei, and to the mechanisms of vector-meson production. LHCb has studied production of the $J/\psi$ and $\psi(2S)$ charmonium states in peripheral and ultra-peripheral collisions using PbPb data at forward rapidity, obtaining the highest precision currently accessible. Here we will present these measurements, along with comparisons with the latest theoretical models and with results from other experiments. Future UPC measurements with the upgraded LHCb detector in Run 3 will also be discussed.

Sprecher: Qiuchan Lu (South China Normal University (CN))

UPC_HP2023_QiuchanLU_final.pdf

11:10 Minijet quenching in a concurrent jet+hydro evolution and the nonequilibrium quark-gluon plasma

Minijets, created by perturbative hard QCD collisions at moderate energies, can represent a significant portion of the total multiplicity of a heavy-ion collision event. Since their transverse momenta are larger than the typical saturation scale describing the bulk of the equilibrating QGP, they do not in general hydrodynamize at the same pace than the bulk of the collision. In this work we make use of a new concurrent minijet+hydrodynamic framework in which the properties of the fluid QGP are modified due to the injection of energy and momentum from the minijets. In order to achieve a realistic description of charged particle multiplicity, the amount of entropy associated to the low-$x$ initial state needs to be reduced. Moreover, the fact that the injected momentum from the randomly oriented minijets is not correlated with the spatial gradients of the system reduces overall flow, and the value of the QGP transport coefficients needs to be reduced. They are, in effect, an important new source of fluctuations. We avow that their abundance makes it necessary to include their physics in holistic descriptions of heavy-ion collisions. We discuss the impact of the minijets on a number of observables, such as $p_T$ spectra and $p_T$-differential flow $v_n$ for a wide range of centrality classes.

Based on: Minijet quenching in a concurrent jet+hydro evolution and the nonequilibrium quark-gluon plasma, D. Pablos, M.Singh, C. Gale, S. Jeon. Phys.Rev.C 106 (2022) 3, 034901

Sprecher: Charles Gale (McGill University)

Gale_HP_2023_fnl.pdf

11:30 Measurement of dijet production in UPC with the ATLAS detector

In relativistic heavy ion collisions, the charged ions produce an intense flux of equivalent photons. Thus, photon-induced processes are the dominant interaction mechanism when the colliding nuclei have a transverse separation larger than the nuclear diameter. In these ultra-peripheral collisions (UPCs), the photon provides a clean, energetic probe of the partonic structure of the nucleus, analogous to deep inelastic scattering. This talk presents a measurement of jet production in UPCs performed with the ATLAS detector using high-statistics 2018 Pb+Pb data. Events are selected using requirements on jet production, rapidity gaps, and forward neutron emission to identify photo-nuclear hard-scattering processes. The precision of these measurements is augmented by studies of nuclear break-up effects, allowing for detailed comparisons with theoretical models in phase-space regions where significant nuclear PDF modifications are expected but not strongly constrained by existing data.

Sprecher: Benjamin Gilbert (Columbia University (US))

HP23_Talk_Gilbert.pdf

11:50 Rapidity-dependent fluctuations in the Trento initial state model

We construct an improved 3+1D version of the Trento initial state model, which includes rapidity-dependent fluctuations. The correlation between the fluctuations at different rapidities is controlled by a new parameter. We then use this improved model to study rapidity-dependent observables for ultracentral collisions. It it known that ultracentral flow at midrapidity is sensitive to fluctuations in the initial state, and it is likewise expected that rapidity-dependent flow will be sensitive to the correlation of these fluctuations between different rapidities in the initial state.

Sprecher: Govert Nijs (Massachusetts Institute of Technology)

HardProbesGovertNijs.pdf

12:10 Simulating hard probes in the early-stages of heavy-ion collisions

We study the impact of the Glasma fields, used to describe the very-early stage of heavy-ion collisions, on the transport of hard probes, namely heavy quarks and jets. We perform numerical simulations of the strong classical fields using techniques from real-time lattice gauge theory. The resulting fields are used as background for the classical transport of ensembles of particles, described by Wong's equations. We develop a numerical solver for the transport of the probes, based on colored particle-in-cell methods.

We focus on the dynamics of heavy quarks and jets in the classical colored fields. To quantify the effect of the Glasma, we extract momentum broadening of hard probes and evaluate the anisotropy transfer from the Glasma to the probes. We investigate other ways to measure the imprint of the Glasma, such as two-particle angular correlations of quark pairs or gauge invariant correlators of color Lorentz forces exerted on the probes.

A. Ipp, D. I. Muller, D. Schuh - Jet momentum broadening in the pre-equilibrium Glasma
P. Khowal, S. K. Das, L. Oliva, M. Ruggieri - Heavy quarks in the early stage of high energy nuclear collisions at RHIC and LHC
D. Avramescu, V. Băran, V. Greco, A. Ipp, D. I. Müller, M. Ruggieri - Simulating jets and heavy quarks in the early stages of heavy-ion collisions using the colored particle-in-cell method (in preparation)

Sprecher: Dana Avramescu (University of Jyväskylä)

DA - HP in Glasma.pdf

10:50 → 12:30 Parallel: Heavy Flavours & Quarkonia

Sitzungsleiter: Ionut Cristian Arsene (University of Oslo)

10:50 A microscopic model of charmonia production in heavy ion collisions

Charmonia production in RHIC is one of the best probes of the QGP state of matter which is created in those collisions. However, the genuine origin of such charmonia is under debate: statistical hadronisation (SH) model considers them as formed at the freeze out while transport models contain 2 components : the primordial charmonia, produced early and subject to decay rate as well as the continuous regenerated component enabled once the local temperature falls below the dissociation temperature. While the SH and transport models can describe the present data, they suffer from some shortcomings.
In our new approach (arxiv 2206.01308), we take strong inspiration from the open quantum system method and propose a microscopic model based on the evaluation of a creation/destruction rate (following Remler's model) from the set of all c and cbar correlated trajectories generated by combining c and cbar scatterings with the QGP and c-cbar potential estimated from lQCD calculations. This allows to describe the continuous generation of charmonia over time while preserving essential features of the quantum transport.
Comparison with LHC data demonstrates that our model is able to reproduce the global trends. In a 2nd version of our model to be presented at HP, we implement our approach in the newly relased EPOS4 and study in particular the role of c-cbar corrrelations in the initial stage as well as the contribution of the excited states, missing in the 1rst version of our model.

Sprecher: Pol Gossiaux (Subatech)

Gossiaux_HP.pdf

Gossiaux_HP.pptx

11:10 The measurements of J/$\psi$ production in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV with ALICE

Quarkonia are excellent probes of deconfinement in heavy-ion collisions. For J/$\psi$, a bound state of ${c}\bar{c}$ quarks, its production yield is sensitive to color screening and dissociation in the medium. However, at LHC energies, the charmonium regeneration is expected to be significantly larger than at RHIC and SPS energies, since the density of uncorrelated charm-anticharm ($c\bar{c}$) pairs in the medium is larger. On the other hand, the determination of the non-prompt component of the J/$\psi$ production, originating from b-hadron decays, allows one to access the interaction of b-quarks with the QGP. It enables as well for prompt J/$\psi$ measurements a direct comparison with prompt charmonium models.

In this talk, new published inclusive J/$\psi$ yield and nuclear modification factor results at midrapidity and forward rapidity, will be shown in Pb–Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. The J/$\psi$-to-D$^{0}$ meson ratio, obtained in central and semicentral collisions, will also be discussed. The preliminary measurements of prompt and non-prompt J/$\psi$ yields and nuclear modification factors, performed at midrapidity in Pb–Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV, will be presented. The determination of the non-prompt J/$\psi$ fraction extends down to very low $p_{\rm T}$ with a significantly improved precision compared to previous publications. Results will be compared with available calculations.

Sprecher: Pengzhong Lu

HPPresentation.pdf

11:30 Measurement of heavy quarkonia elliptic flow in pPb collisions with the CMS detector

The second-order Fourier coefficients ($v_{2}$) of $\Upsilon$(1S) and J/$\psi$ mesons in high-multiplicity pPb collisions is studied using data collected by the CMS experiment at a nucleon-nucleon center-of-mass energy 8.16 TeV. The dimuons used to reconstruct the heavy quarkonium states are correlated with charged hadrons using long-range two-particle correlation techniques. The measurement of the $\Upsilon$(1S) $v_{2}$ is reported for the first time in small collision systems. The results are discussed in the context of collectivity and modification of heavy quark dynamics.

Sprecher: Kisoo Lee (Korea University (KR))

HP_2023_KisooLee_v5.pdf

11:50 New approach of charmonium medium response using elliptic and triangular flow of J/$\psi$ and $\psi$(2S) with CMS

The second- and third-order Fourier coefficients of charmonium states are measured in PbPb collisions with CMS. With this new analysis, extending to a higher $p_\mathrm{T}$ region, we investigate further the high-$p_\mathrm{T}$ J/$\psi$ $v_{2}$ in heavy ion collisions. The nonprompt J/$\psi$ $v_{2}$ probes the different behavior of charm and bottom quarks induced by interactions with the QGP medium. The $v_{3}$ flow coefficient values, for the separated prompt and nonprompt J/$\psi$ as well as the prompt $\psi$(2S), are reported for the first time.

Sprecher: Geonhee Oh (University of Illinois at Chicago)

Geonhee_CharmoniaFlowCMS_HP23.pdf

12:10 Quarkonium transport in strongly coupled plasmas

Suppression of open heavy flavors and quarkonia in heavy-ion collisions is among the most informative probes of the quark-gluon plasma. Interpreting the full wealth of data obtained from the collision events requires a precise understanding of the evolution of heavy quarks and quarkonia as they propagate through the nearly thermal and strongly coupled plasma. Only in the past few years, systematic theoretical studies of quarkonium time evolution in the QGP have been carried out in the regime where the temperature of the QGP is much smaller than the inverse of quarkonium size.

Such calculations require the evaluation of a gauge-invariant correlator of chromoelectric fields dressed with Wilson lines, which is similar to, but different from, the correlation used to define the well-known [1] heavy quark diffusion coefficient. The origin of this difference has been explained in [2-4]. In this talk, we will show a calculation of the analogous correlator in strongly coupled $\mathcal{N}=4$ SYM using the AdS/CFT correspondence at a finite temperature [5]. While it resembles the open heavy quark case, it has some crucial differences that highlight the relevance of quantum color correlations. We will also discuss the results for the quarkonium transport coefficients obtained from this correlator, thereby establishing the first analytic results at strong coupling in this context.

[1] Phys. Rev. D 74 (2006) 085012; [2] JHEP 01 (2022) 137; [3] arXiv:2205.04477; [4-5] in preparation

Sprecher: Bruno Scheihing Hitschfeld (Massachusetts Institute of Technology)

HPTalk-Bruno_Scheihing.pdf

10:50 → 12:30 Parallel: Jets and their modification in QCD Matter: I

Sitzungsleiter: Marta Verweij

10:50 Hard parton dispersion in the quark-gluon plasma, non-perturbatively

Jet-medium interactions receive large non-perturbative contributions from classical gluons, i.e. infrared gluons with high occupation numbers. These contributions affect transverse jet momentum broadening and medium-induced radiation. Both depend significantly on the in-medium dispersion of hard partons, encoded in their so-called asymptotic mass.
In this talk, I shall show how the analytical properties of thermal amplitudes allow for a non-perturbative determination of the IR classical contribution through lattice determinations in the dimensionally-reduced Effective Theory of hot QCD, EQCD. I will show how these existing lattice determinations need to be complemented by perturbative two-loop matching calculations in EQCD and QCD, so that the unphysical (classical) UV behaviour of EQCD is replaced by its proper quantum QCD counterpart. I will show how lattice and perturbative EQCD are in excellent agreement in the UV and I will discuss the numerical effect of the two-loop quantum QCD contribution, with an outlook on the effect on medium-induced radiation rates.
The talk is based on G.D. Moore, N. Schlusser 2009.06614, J. Ghiglieri, G.D. Moore, P. Schicho, N. Schlusser 2112.01407, J. Ghiglieri, P. Schicho, N. Schlusser, E. Weitz, in preparation

Sprecher: Jacopo Ghiglieri (SUBATECH, Nantes)

ghiglieri_HP23.pdf

11:10 Jet shape observables in p+p and Au+Au collisions at sqrt{s_{NN}} = 200 GeV at STAR

Jets produced from hard scatterings of partons early in heavy-ion collisions traverse through the quark-gluon plasma (QGP) medium and get modified relative to vacuum ($p$+$p$ collision) baseline. These modifications can change the distributions of jet shape observables, which are related to jet fragmentation and its internal structure, and calculated based on the intra-jet angular energy distribution. LHC results showed medium-induced modifications to differential jet shape ($\rho(r)$, radial distribution of constituents relative to the jet axis) distributions and a prevalence of quark-like fragmentation from Girth (jet angularity), $p_T^D$ (jet momentum dispersion) and LeSub (splitting between leading and subleading jet constituents) measurements. At RHIC, we are able to study lower energy jets, complementary to those measured at the LHC. Hence measurements of jet shapes at RHIC can help constrain models at different energy scales. In this talk, we present measurements of the fully corrected $\rho(r)$ in $p$+$p$ and Au+Au collisions at $\sqrt{s_{\rm NN}} = 200$ GeV collected by the STAR experiment. We also show fully corrected resutls for Girth, $p_T^D$ and LeSub in $p$+$p$ collisions. Exploratory studies of these observables in Au+Au collisions will also be discussed.

Sprecher: Tanmay Pani (Rutgers University)

HP2023.pdf

11:30 Recoil-free jet observable in heavy ion collisions

We will discuss the use of recoil-free jet observables to systematically benchmark jet modification studies with precision and sensitivity, starting from the hardest components of jets. Here we focus on the recoil-free jet axis in defining di-jet and photon-jet angular decorrelation. This observable is not affected by the huge underlying event background and can be calculated and measured precisely. Also, since the recoil-free axis follow the dominant energy flow within jet, it is sensitive to any partonic energy loss mechanism which can deflect the axis direction. We will present Monte Carlos studies based on simulations with different jet quenching models. Future measurements of this observable will allow us to test the onset of jet quenching in the whole jet evolution history. This paves a path towards precision heavy ion jet modification studies using recoil-free observables.

Sprecher: Bin Wu (Universidade de Santiago de Compostela)

Talks.pdf

11:50 Classical vs. Quantum Corrections to Jet Broadening in a Weakly Coupled Quark-Gluon Plasma

The transverse momentum broadening coefficient serves as a key ingredient in characterising the quenching of a jet as it propagates through the QGP. While it has recently been understood to receive quantum, radiative corrections featuring potentially large logarithmic enhancements at relative order $g^2$ [1, 2], it is still not clear how these corrections compare quantitatively with their classical counterparts, i.e, those coming from the exchange of thermal gluons with large occupation number, present at relative order $g$ and higher [3–5].

During the talk, I plan to first motivate the need for a more careful calculation of the aforementioned logarithmic corrections in the case of a weakly coupled QGP. I will then sketch how the argument of the leading logarithm is altered with respect to earlier calculations and furthermore, how the phase space giving rise to these logarithmic corrections is smoothly connected to that from which the classical corrections emerge. Finally, I will conclude by discussing how these findings, detailed in our own work [6] are relevant with respect to the overall goal of determining which class of corrections are quantitatively more important.

[1] T. Liou, A. Mueller and B. Wu 1304.7677
[2] J.P. Blaizot, F. Dominguez, E. Iancu and Y. Mehtar-Tani 1311.5823
[3] S. Caron-Huot 0811.1603
[4] M. Panero, K. Rummukainen and A. Sch ̈afer 1307.5850
[5] G.D. Moore and N. Schlusser 1911.13127
[6] J. Ghiglieri and E. Weitz 2207.08842

Sprecher: Eamonn Weitz (SUBATECH, Univeristé de Nantes)

23_hp_weitz.pdf

12:10 Observation of medium-induced yield enhancement and acoplanarity broadening of low-$p_{\rm T}$ jets in pp and Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV with ALICE

The measurement of jets recoiling from a trigger hadron provides unique probes of medium-induced modification of jet production. Jet deflection via multiple soft scatterings with the medium constituents or single-hard Molière scatterings off quasi-particles in the medium are expected to modify the azimuthal correlation between the trigger hadron and recoiling jet. The $R$-dependence of recoil jet yield also probes jet energy loss and intra-jet broadening. In this talk we present measurements of the semi-inclusive distribution of charged-particle jets recoiling from a trigger hadron in pp and Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV. We employ precise, data-driven subtraction of the large uncorrelated background contaminating the measurement in Pb-Pb collisions, enabling the exploration of medium-induced modification of jet production and acoplanarity over a wide phase space, including the low jet $p_\mathrm{T}$ region for large jet resolution parameter $R$. Hadron-jet acoplanarity in pp collisions will be also presented, which provides a sensitive test of pQCD calculations, as well as a crucial data reference for in-medium jet deflection studies in Pb-Pb collisions. We observe that the jet yield at low $p_\mathrm{T}$ and at large azimuthal angle between the trigger hadron and jet is significantly enhanced in Pb-Pb collisions with respect to pp collisions. Comparison to theoretical calculations incorporating jet quenching will also be discussed.

Sprecher: Yongzhen HOU (CCNU & IPHC)

HP2023_recoilJets_Yongzhen.pdf

10:50 → 12:30 Parallel: Jets and their modification in QCD Matter: II

Sitzungsleiter: Xin-Nian Wang

10:50 On the momentum broadening of in-medium jet evolution using a light-front Hamiltonian approach

Following the formalism developed in our preceding works [1], a non-perturbative light-front Hamiltonian approach, we investigated the momentum broadening of a quark jet inside a SU(3) colored medium. We performed the numerical simulation of the real-time jet evolution in the Fock space of |q> + |qg>, at an extensive range of $p^+$, and various medium densities. With the obtained light-front wavefunctions of the quark jet, we extracted the jet's observables, including its transverse momentum distribution, the quenching parameter, and the gluon emission rate. We analyzed the interplay between the medium-induced gluon emission and the momentum broadening. This work provides an enhanced understanding of jet quenching from non-perturbative perspectives.

[1] M. Li, T. Lappi, and X. Zhao, ``Scattering and gluon emission in a color field: A light-front Hamiltonian approach'', Phys. Rev. D 104 (2021) no.5, 056014; arXiv:2107.02225 [hep-ph].

Sprecher: Meijian Li (University of Santiago de Compostela)

HP2023_Jet_tBLFQ_MeijianLi.pdf

11:10 Exploring medium properties with hard transverse momentum splittings using groomed jet substructure measurements in Pb-Pb collisions with ALICE

Jet substructure observables provide unique probes of the properties of the quark-gluon plasma (QGP). In this talk, we report new measurements of groomed jet substructure in central Pb-Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV. We present the first application of Dynamical Grooming in heavy-ion collisions to search for excess $k_{\mathrm{T,g}}$ emissions as a signature of point-like scattering, which is sensitive to large-angle scattering of jets off of quasi-particles in the QGP. These results are reported for the first time in central Pb-Pb collisions and over a larger jet $p_{\mathrm{T}}$ range than reported previously. Additionally, we present measurements employing both the Soft Drop and Dynamical Grooming algorithms, comparing results in central Pb-Pb, semicentral Pb-Pb, and pp collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV. Results with grooming methods and parameters will also be compared. The techniques developed for this measurement are more broadly applicable to jet substructure, which we will explore further in this talk. Comparisons to model calculations will also be discussed.

Sprecher: Raymond Ehlers (Lawrence Berkeley National Laboratory/UC Berkeley)

2023-03-28.rehlers.alice_hardest_ktg_hard_probes_2023.v6.pdf

11:30 Jet evolution in a dense medium beyond multiple soft scattering approximation

In a series of recent publications [1,2,3], we have proposed a factorized approach, based on perturbative QCD, for the evolution of a jet in a dense quark-gluon plasma, together with its implementation as a Monte-Carlo parton shower and successful applications to the phenomenology of jet quenching.
In the original formulation of the parton shower, the collisions between the jet constituents and those of the plasma have been treated in the multiple soft scattering approximation, thus neglecting important effects from single hard scattering. In this new work [4], we extend our Monte Carlo by including the effects of single scattering both on the transverse momentum broadening and on the spectrum for medium-induced radiation. To that aim, the medium-induced cascade is simulated in full 3+1 dimensions and collisions are generated dynamically. This allows us to complete the BDMPS-Z sector of the spectrum for medium-induced radiation with the GLV (Gyulassy-Levai-Vitev) tail at high energies and the Bethe-Heitler spectrum at low energies.
Finally, we discuss the impact of single hard scattering on jet substructure observables like the $k_{t,g}$-distribution after Soft Drop, as measured by the ALICE Collaboration.

Refs:
[1] Caucal, Iancu, Mueller, Soyez, PRL 120 (23), 232001
[2] Caucal, Iancu, Soyez, JHEP 2019 (10), 1-55
[3] Caucal, Iancu, Soyez, JHEP 2021 (4), 1-38
[4] Caucal, Iancu, Soyez, in preparation.

Sprecher: Dr. Edmond Iancu (IPhT, CEA-Saclay)

Iancu-HP2023.pdf

11:50 Jet quenching studies with new jet substructure and suppression measurements in ATLAS

Measuring the jet substructure in heavy-ion collisions provides exciting new opportunities to study detailed aspects of the dynamics of jet quenching in the hot and dense QCD medium created in these collisions. In this talk, we present new ATLAS measurements of jet substructure performed using various jet (de)clustering and grooming techniques. Measurements of inclusive jet suppression ($R_{AA}$) in heavy-ion collisions are presented as a function of the jet substructure using both small-radius ($R=0.4$) and large-radius ($R=1.0$) jets in Pb+Pb and $pp$ collisions at $\sqrt{s_{NN}} = 5.02$ TeV. The jet substructure is characterized using the Soft-Drop grooming procedure in order to identify subjets corresponding to the hardest parton splitting in the jet. The measurements are performed using different jet constituents such as charged tracks, smaller $R$ calorimeter jets, and novel objects reconstructed using tracker and calorimeter information. The dynamics of jet quenching is measured and presented as a function of the transverse momentum scale ($\sqrt{d_{12}}$) and the angle of the hardest splitting in the jet. These new measurements test the sensitivity of jet suppression in the QCD medium to its substructure and the emergence of a critical angle for the onset of color decoherence.

Sprecher: Martin Rybar (Charles University)

HP2023_Rybar.pdf

12:10 Energy loss effects in EECs at LO

In recent years, there has been an effort towards establishing a more complete picture for jet substructure in the presence of the quark gluon plasma. Such a program requires not only a more detailed description of medium induced effects, but also the design of novel substructure observables. Very recently, it has been noticed that energy-energy correlators (EECs) might provide one type of such observables. Although the full extent of their sensitivity to the medium has not been completely explored, they are capable to resolve the transverse structure of the jet. In particular, they are sensitive to the critical angle separating coherent and decoherent jet evolution in the medium. In this talk, we show for the first time the effects of medium induced radiative energy loss in EECs at leading order in the number of vacuum-like emissions. The calculation takes into account all order soft gluon emissions, in the large $N_c$ limit and neglecting subdominant interfering contributions. Similar to other jet quenching observables, energy loss leads to an overall suppression of the EECs. More importantly, this is accentuated in the decoherent regime and results in an important competing effect when trying to extract the critical angle. We further comment on how the current calculation can be extended beyond leading order accuracy, important to compute more complex observables.

Sprecher: Joao Barata (BNL)

Barata_HP23.pdf

12:30 → 14:00 Lunch

14:00 → 16:00 Parallel: Electromagnetic & Electroweak Probes

Sitzungsleiter: Alexander Milov (Weizmann Institute of Science)

14:00 Probing the initial state of nuclear collisions using isolated prompt photons with ALICE

Hadronic collisions produce prompt photons that are characterized by a large transverse momentum and absence of event activity in their vicinity. Photons are a robust probe of cold nuclear matter effects in small and large collision systems because they do not interact strongly and are thus insensitive to medium-induced final-state effects. Prompt photon production is dominated by the Compton process ($g\text{q}\rightarrow \text{q}\gamma$), making it sensitive to the gluon parton distribution function (PDF), and provides a test of high momentum pQCD calculations. Recent experimental results indicate the need for corrections beyond NLO to describe their production accurately. This talk presents the measurement of isolated prompt photon production in pp and p-Pb collisions at $\sqrt{s_\mathrm{NN}}=8$ TeV, measured by ALICE. The isolation method is applied to suppresses the background photons produced in the fragmentation process and electromagnetic decays. The production cross sections in both systems will be presented and compared with NLO calculations using recent (n)PDFs and fragmentation functions. In addition, the nuclear modification factor $R_{\rm pA}$ is measured, quantifying possible modifications of the parton distributions inside the nucleus. This is the first time the isolated prompt photon $R_{\rm pA}$ has been measured for low transverse momenta of $p_{\mathrm{T}} < 20 $ GeV/$c$ - a regime in which a sizeable suppression is predicted by theoretical calculations.

Sprecher: Florian Jonas (Uni Muenster/ORNL)

isoPhotonsALICE_Final.pdf

14:20 Dilepton production and BSM physics from photon fusion processes in UPC and non-UPC Pb+Pb collisions with the ATLAS detector

Relativistic heavy-ion beams at the LHC are accompanied by a large flux of equivalent photons, leading to multiple photon-induced processes. This talk presents a series of measurements of dilepton production from photon fusion performed by the ATLAS Collaboration, which provide strong constraints on the nuclear photon flux, its dependence on the impact parameter and photon energy, and can also probe physics beyond the standard model (BSM) using tau leptons. Recent measurements of exclusive dielectron production in ultra-peripheral collisions (UPC) are presented. Comparisons of the measured cross-sections to QED predictions from the Starlight and SuperChic models are also presented. Furthermore, measurements of muon pairs produced via two-photon scattering processes in hadronic (i.e. Non-UPC) Pb+Pb collisions are discussed. These non-UPC measurements provide a novel test of strong-field QED and may be a potentially sensitive electromagnetic probe of the quark-gluon plasma. These measurements include the dependence of the cross-section and angular correlation on the mean-$p_\mathrm{T}$ of the dimuon pair, the rapidity separation between the muons, and the pair angle relative to the second-order event-plane, all measured differentially as a function of the Pb+Pb collision centrality. The presented results are compared with recent theory calculations. Tau-pair production measurements can constrain the tau lepton's anomalous magnetic dipole moment (g-2), and a recent ATLAS measurement using muonic decays of tau leptons in association with electrons and tracks provides one of the most stringent limits available to date.

Sprecher: Iwona Grabowska-Bold (AGH University of Science and Technology)

HP2023-GammaGammaAtlas-032023.pdf

14:40 Comparative multi-probe study of jet energy-loss in QGP

An important sign of the creation of the Quark-Gluon Plasma in heavy-ion collisions is the observation of jet energy-loss. Energetic, high transverse momentum ($p_{T}$) partons produced at the moment of initial hard scattering are influenced by the evolution history of the medium and lose energy via interactions. In this work we compare two models of low virtuality radiative energy loss: MARTINI [1] and CUJET [2] using the JETSCAPE framework. We integrate CUJET into the JETSCAPE workflow and perform full jet simulations using DGLV [3-5] radiative rates, for the first time. We consider strongly interacting probes (charged hadrons, jets, jet shape and jet fragmentation function) as well as electromagnetic probes; photons from jet-medium interactions have a similar structure to the gluon radiation channel but experience no final state interactions [6]. We present the first realistic calculation of jet-medium photons from CUJET and compare it to jet-medium photons from MARTINI. We find that these photons contribute significantly in the phenomenologically interesting intermediate $p_T$ domain ($4$-$12$ GeV).
[1] B. Schenke et al., Phys.Rev.C 80 (2009) 054913
[2] J. Xu et al., JHEP 08 (2014) 063
[3] M. Gyulassy et al., Nucl.Phys.B 571 (2000) 197-233
[4] M. Gyulassy et al., Nucl.Phys.B 594 (2001) 371-419
[5] M. Djordjevic et al., Nucl.Phys.A 733 (2004) 265-298
[6] C. Gale et al., Phys.Rev.C 105 (2022) 1, 014909

Sprecher: Herr Rouzbeh Modarresi-Yazdi (McGill University)

RMY_JetMetPhotons_HP_2023.pdf

15:00 Thermal radiation and direct photon production in Pb-Pb and pp collisions with dielectrons in ALICE

Electromagnetic probes such as photons and dielectrons are a unique tool to study the space-time evolution of the hot and dense matter created in ultrarelativistic heavy-ion collisions. At low dielectron invariant mass ($m_{\rm ee}$), thermal radiation from the hot hadronic phase contributes to the dielectron spectrum via decays of $\rho$ mesons, whose spectral function is sensitive to chiral-symmetry restoration. At larger $m_{\rm ee}$, thermal radiation from the quark–gluon plasma carries information about the early temperature of the medium. At LHC energies, it is nevertheless dominated by a large background from correlated heavy-flavour hadron decays affected by energy loss and flow in the medium. Complementary to the real photon measurements, dielectron data also allow the extraction of the real direct photon fraction, including thermal photons at low pair transverse momentum $p_{\rm T,ee}$. In pp collisions, such measurement serves as a fundamental test of perturbative QCD calculations, and as a baseline for the studies in heavy-ion collisions. This talk will present the latest ALICE results on dielectron studies in Pb-Pb, and in minimum-bias and high-multiplicity pp collisions, at $\sqrt{s_{\rm NN}}$ = 5.02 TeV and 13 TeV, respectively. The measurements are compared to simulations and expectations from theory.
Finally, the status of the Run 3 analysis will be reported.

Sprecher: Raphaelle Bailhache

28_03_2023.pdf

15:20 Enhancement of photon momentum anisotropies during the late stages of relativistic heavy-ion collisions

We present a consistent photon production calculation from hadronic cross sections, including bremsstrahlung and 2-to-2 reactions, matching the usually employed thermal rates [1,2]. Using the hadronic transport approach SMASH as the afterburner for the hadronic stage at RHIC and LHC energies, we find a significant increase in the calculated momentum anisotropies of these photons due to microscopic non-equilibrium dynamics. This enhancement is found in comparison to standard calculations, which rely on the folding of equilibrium rates to a hydrodynamical evolution. Once combined with photons produced above the particlization temperature in the hydrodynamical evolution, the differences between the two approaches are modest regarding $p_\perp$-differential spectra, but are clearly noticeable at low for the elliptic flow: non-equilibrium dynamics enhance the photon $v_2$ below $p_\perp\approx 1.5$ GeV.

References
[1] A. Schäfer, O. G-M., J-F. Paquet, H. Elfner, and C. Gale. Phys.Rev.C 105 (2022) 4, 044910, arXiv: 2111.13603

[2] A. Schäfer, J. M. Torres-Rincon, J. Rothermel, N. Ehlert, C. Gale and H. Elfner. Phys.Rev.D 99 (2019) 11, 114021. arXiv: 2111.13603

Sprecher: Prof. Hannah Elfner (GSI Darmstadt)

Elfner_HP23.pdf

15:40 Recent ALICE results on photon-lead interactions

Photon-induced reactions in ultra-peripheral collisions (UPCs) of heavy nuclei at the LHC have been studied using the ALICE detector for several years. The ALICE detector can measure the photoproduction cross section for vector mesons at various rapidities, centre-of-mass energies and collision systems. Beyond the recent ALICE studies of the rapidity and momentum transfer dependence of coherent $\rm{J/\psi}$ photoproduction, new results on incoherent $\rm{J/\psi}$ photoproduction will be discussed. These results complement coherent $\rm{J/\psi}$ measurements and provide additional sensitivity to probing nuclear gluon effects including the presence of subnucleon gluon fluctuations. Additionally, new measurements of the coherent and incoherent $\rm{J/\psi}$ polarization will be shown. These new results serve for testing the s-channel helicity conservation hypothesis.

Sprecher: Roman Lavicka (Stefan Meyer Institute of the Austrian Academy of Sciences)

hp23_rl.pdf

14:00 → 16:00 Parallel: Future Experimental Facilities

Sitzungsleiter: Luciano Musa

14:00 New opportunities for understanding high-density QCD matter with CMS Phase II detector at the High-Luminosity LHC era

The intriguing phenomena emerging in the high-density QCD matter are being widely studied in the heavy ion program at the LHC and will be understood more deeply during the high luminosity LHC (HL-LHC) era. The CMS experiment is under the Phase II upgrade towards the HL-LHC era. A new timing detector is proposed with timing resolution for minimum ionization particles (MIP) to be 30ps. The MIP timing detector (MTD) will provide the particle identification (PID) ability with a large acceptance covering up to $\eta<3$ through time-of-flight (TOF). Combining MTD with the other new sub-detectors, a tracker with acceptance $\eta<4$, high granularity calorimeters with acceptance covering $\eta<5$, will enable the deep studies of high-density QCD matters in ultra-relativistic heavy ion collisions. In this presentation, the performances of a broad range of measurements in heavy ion programs will be discussed using TOF-PID. These include the (3+1)D evolution of heavy flavor quarks, QGP medium response to high-$p_\mathrm{T}$ parton energy loss at wide jet cone angles, collectivity in small systems, fluctuations and transport of initially conserved charges, and light nuclei physics.

Sprecher: Yen-Jie Lee (Massachusetts Institute of Technology)

20230328-HP2023-yenjie-v6.pdf

14:20 ALICE 3: a next-generation heavy-ion detector for LHC Run 5 and 6

ALICE 3 is proposed as the next-generation experiment to address unresolved questions about the quark-gluon plasma by precise measurements of heavy-flavour probes as well as electromagnetic radiation in heavy-ion collisions in LHC Runs 5 and 6. In order to achieve the best possible pointing resolution a concept for the installation of a high-resolution vertex tracker in the beam pipe is being developed. It is surrounded by a tracker based on monolithic active CMOS pixel sensors covering roughly 8 units of pseudorapidity. To achieve the required particle identification performance, a combination of a time-of-flight system and a Ring-Imaging Cherenkov detector is foreseen. Further detectors, such as an electromagnetic calorimeter, a muon identifier, and a dedicated forward detector for ultra-soft photons, are being studied. In this presentation, we will explain the detector concept and its physics reach as well as discuss the R&D challenges.

Sprecher: Alessandro Grelli (Utrecht)

ALICE3_Grelli_HP2023.pdf

14:40 Heavy flavor physics at the sPHENIX experiment

In Spring 2023, the sPHENIX detector at BNL’s Relativistic Heavy Ion Collider (RHIC) will begin measuring a suite of unique heavy flavor and quarkonia observables with unprecedented statistics and kinematic reach at the RHIC energies using combined EM and hadronic calorimeters and high precision tracking. A MAPS-based vertex detector upgrade to sPHENIX, the MVTX, will provide a precise determination of the impact parameter of tracks relative to the primary vertex in high multiplicity heavy-ion collisions and polarized proton-proton/proton-nuclei collisions. It will enable precision measurements of open heavy-flavor observables, covering an unexplored kinematic region at RHIC. The physics program, its potential impact, and the recent detector development will be discussed in this talk.

Sprecher: Antonio Carlos Oliveira da Silva (Iowa State University)

HardProbes2023_v4.pdf

15:00 Measurement of a caloric curve and chiral symmetry restoration with the NA60+ experiment at the CERN SPS

The high-intensity beams provided by the CERN SPS in a wide energy interval offer a unique opportunity to investigate the region of the QCD phase diagram at high baryochemical potential. The NA60+ experiment, proposed for taking data with heavy-ion collisions at the SPS in the next years, has a strong potential for investigating the QCD phase diagram via measurements of rare probes in a beam-energy scan of Pb-Pb and p-A collisions in the interval √s$_{NN}$ = 6-17 GeV.
In this talk the physics program of the NA60+ on thermal dimuons will be described.
At beam energies below top SPS energy, the baryon density becomes maximal and its effect on $\rho$ meson broadening can be measured by NA60+ with utmost precision.
NA60+ will have sensitivity to the $\rho − a_1$ chiral mixing mechanism, which provides access also to the properties of the $a_1$ by exploring the thermal dimuon mass spectrum in the range 1 < M < 1.4 GeV.
For dimuon masses above 1.5 GeV, the temperature of the emitting source can be directly extracted by a fit of the mass spectrum. The experimental program of NA60+ plans to determine for the first time a caloric curve by measuring the temperature vs beam energy, with particular focus on √s$_{NN}$ < 10 GeV, which is believed to be essential to map out the phase transition regime at high $\mu_B$.
Finally, the competitiveness and complementarity of NA60+ in the landscape of the experiments foreseen at other facilities in the next decade will be discussed.

Sprecher: Gianluca Usai (University of Cagliari and INFN)

HP2023-usai.pdf

15:20 The ALICE Forward calorimeter

The addition of a Forward Calorimeter (FoCal) to the ALICE experiment is proposed for LHC Run 4 to provide unique constraints on the low-x gluon structure of protons and nuclei via forward measurements of direct photons. A new high-resolution electromagnetic Si-W calorimeter using both Si-pad and Si-pixel layers is being developed to discriminate single photons from pairs of photons originating from $\pi^0$ decays. A conventional sampling hadron calorimeter is foreseen for jet measurements and the isolation of direct photons. In this presentation, we will report on results from recent test beam campaigns at CERN with Si-pad and pixel modules, a first prototype for the hadronic calorimeter, as well as the physics prospects.

Sprecher: Tatsuya Chujo (University of Tsukuba)

HP2023_FoCal_chujo_v04.pdf

15:40 ITS3: A truly cylindrical inner tracker for ALICE

After the successful installation and first operation of the upgraded Inner Tracking System (ITS2), which consists of about 10 m$^2$ of monolithic silicon pixel sensors, ALICE is pioneering the usage of bent, wafer-scale pixel sensors for the ITS3 for Run 4. Sensors larger than typical reticle sizes can be produced using the technique of stitching. At thicknesses of about 30 µm, the silicon is flexible enough to be bent to radii of the order of 1 cm. By cooling such sensors with a forced air flow, it becomes possible to construct a detector with minimal material. The reduction of the material budget and the improved pointing resolution will allow new measurements, in particular of heavy-flavour decays and electromagnetic probes. In this presentation, we will report on the sensor developments, the performance of bent sensors in test beams, and the mechanical studies on truly cylindrical layers.

Sprecher: Jory Sonneveld

20230328_Sonneveld_ALICE_ITS3.pdf

14:00 → 16:00 Parallel: Heavy Flavours & Quarkonia

Sitzungsleiter: Dr. Zi-Wei Lin

14:00 $\Upsilon$(nS) meson production in Pb+Pb and $pp$ collisions with ATLAS

Measurements of bottomonium states in heavy-ion collisions provide a powerful tool to study both initial-state effects on heavy-quark production and final-state interactions between heavy quarks and the quark-gluon plasma (QGP). The ATLAS experiment at LHC has measured the production of bottomonium states $\Upsilon$(1S), $\Upsilon$(2S), and $\Upsilon$(3S), in Pb+Pb and $pp$ collisions at a center-of-mass energy per nucleon pair of 5.02 TeV. The data correspond to integrated luminosities of 1.38 nb$^{-1}$ of Pb+Pb data collected in 2018, 0.44 nb$^{-1}$ of Pb+Pb data collected in 2015, and 0.26 fb$^{-1}$ of pp data collected in 2017. The final ATLAS result on the production of three bottomonium states will be reported. The measurement in Pb+Pb collisions is compared to that in $pp$ collisions to extract the nuclear modification factor, $R_{\mathrm{AA}}$, as a function of event centrality, $p_{\mathrm{T}}$ and rapidity, and compared to several theoretical models. We will also present a new measurement studying the relationship between the production of hard and soft particles through the correlation of Upsilon meson states with the inclusive-charged particle yields. The analysis is performed using the full-luminosity ATLAS Run-2 13 TeV $pp$ data. A description of the technical challenges associated with a heavy-ion style analysis in high-pileup $pp$ data will be shown, as well as the results and their physics implications.

Sprecher: Zvi Citron (Ben-Gurion University of the Negev)

ATLAS_upsilon_hp.pdf

14:20 Exclusive quarkonium photoproduction in nucleus-nucleus UPCs at the LHC in NLO QCD

We present the first study of coherent exclusive quarkonium (J/psi, Upsilon) photoproduction in ultraperipheral nucleus-nucleus collisions (UPCs) at the LHC in the framework of collinear factorization and next-to-leading order (NLO) perturbative QCD. We make predictions for the J/psi and Upsilon rapidity distributions for the cases of lead (Pb) and oxygen (O) beams and quantify their dependence on the choice of the hard scale, nuclear PDFs and their uncertainties, and models for nuclear generalized parton distribution functions (GPDs). We demonstrate that our approach provides a simultaneously good description of all available Run 1 and Run 2 LHC data on J/psi photoproduction in Pb-Pb UPCs and makes definite predictions for photoproduction of heavy quarkonia in heavy-ion UPCs at the LHC.

Sprecher: Kari J Eskola (University of Jyvaskyla)

Eskola_HP2023.pdf

14:40 Spin-Induced Interactions and Heavy-Quark Transport in the QGP

We extend a previously constructed T-matrix approach for heavy quarks in the quark-gluon plasma (QGP) to include inverse-mass (1/M) corrections, i.e. the spin-orbit, spin-spin and tensor forces, between partons. Based on the vacuum Cornell potential as the interaction kernel for the T-matrix equation, we first confirm that the experimental charmonium and bottomonium spectroscopy in vacuum are much improved by employing a confining potential that is a mixture of vector and scalar interactions, rather than a purely scalar one. We then apply the refined potential to calculate the in-medium single-parton spectral functions at finite temperature self-consistently and constrained by various thermal lattice-QCD data. Finally, we study the consequences for the in-medium charm-quark transport coefficients at different temperatures. It turns out that the mixing effect for confining potential significantly enhances the friction coefficient, A(p), for charm quarks in the QGP over previous calculations with a purely scalar potential. Our results may have significant implications for the microscopic description of heavy-flavor transport in heavy-ion collisions at RHIC and the LHC.

Sprecher: Zhanduo Tang

HP23_Zhanduo Tang.pdf

15:00 New measurements in fixed-target collisions at LHCb

The LHCb spectrometer has the unique capability to function as a fixed-target experiment by injecting gas into the LHC beampipe while proton or ion beams are circulating. The resulting beam+gas collisions cover an unexplored energy range that is above previous fixed-target experiments, but below the top RHIC energy for AA collisions. Here we present new results on open charm, $J/\psi$, and $\psi(2S)$ production from pNe and PbNe fixed-target collisions at LHCb. Comparisons with various theoretical models of particle production and transport through the nucleus will be discussed.

Sprecher: Kara Mattioli (Laboratoire Leprince Ringuet, CNRS)

Mattioli Hard Probes Fixed Target.pdf

15:20 A fluid-dynamic approach to heavy-quark diffusion in the quark-gluon plasma

Heavy quarks (i.e. charm and beauty) are powerful tools to characterize the quark-gluon plasma (QGP) produced in heavy-ion collisions. Although they are initially produced out of kinetic equilibrium via hard partonic scattering processes, recent measurements of anisotropic flow of charmed hadrons [1] pose the question regarding the possible thermalization of heavy quarks in the medium. Our recent work [2] provides new insights on the level of thermalization of charm and bottom quarks in the QGP. In particular, exploiting a mapping between transport theory and fluid-dynamics, we will show how a fluid-dynamic description of the dynamics of charm quarks in the QCD plasma is feasible.
We will show results for spectra and flow coefficients of charmed hadrons obtained with a fluid-dynamic code (FluiduM [3]) coupled with the conservation of a heavy-quark - antiquark current in the QGP. We compare our calculations with the most recent experimental data in order to provide further constraints on the transport coefficients of the QGP [4].
This work is funded via the DFG ISOQUANT Collaborative Research Center (SFB 1225).
[1] PLB 813 (2021) 136054
[2] Phys.Rev.D 106 3, 034021 (2022)
[3] Phys. Rev. C 100, 014905 (2019)
[4] Capellino, Beraudo, Dubla, Floerchinger, Grossi, Kirchner, Masciocchi, Selyuzhenkov; in preparation

Sprecher: Federica Capellino (Physikalisches Institut Heidelberg)

HP2023_capellino.pptm

15:40 Detailed study of the nuclear modification of $\Upsilon$ states in pPb and PbPb collisions with CMS

Bottomonia, the heaviest known mesons, represent major probes of strongly interacting matter properties. In the context of nuclear collisions, the binding energies separating the $\Upsilon$(nS) states (n=1, 2, or 3) offer an experimental handle to characterize the medium formed. In this talk, we study the modification of the production of the three $\Upsilon$ mesons in both pPb and PbPb collisions with the latest measurements carried out with the CMS detector. The results are compared with model calculations in order to interpret the data.

Sprecher: JaeBeom Park

HP_2023_v4.pdf

14:00 → 16:00 Parallel: Jets and their modification in QCD Matter

Sitzungsleiter: Urs Achim Wiedemann

14:00 Computing jet transport coefficients on the lattice

The leading jet transport coefficients $\hat{q}$ or $\hat{e}_{2}$ encode transverse or longitudinal momentum broadening of a hard parton traversing a hot medium. Computing their normalization and temperature dependence from first principles is key to appreciating the observed suppression of high-transverse momentum probes at RHIC or LHC collision energies. We present a first continuum extrapolated result of $\hat{q}$ computed on pure SU(3) lattices with non-trivial temperature dependence different from the weak-coupling expectation.

We discuss the formalism published in Refs [1,2] and its challenges and status in view of obtaining $\hat{e}_{2}$ or of unquenching the calculation. We consider a hard quark subject to a single scattering on the plasma. The transport coefficients are factorized in terms of matrix elements given as integrals of non-local gauge-covariant gluon field-strength field-strength correlators. After the analytic continuation to the deep-Euclidean region, the hard scale permits to recast these as a series of local, gauge-invariant operators. The renormalized leading twist term in this expansion is closely related to static quantities, and is computed on pure SU(3) lattices ($n_{\tau}$=4, 6, 8 and 10) for a range of temperatures, ranging from 200MeV < T < 1GeV. Our estimate for the unquenched result in $2+1$-flavor QCD has very similar features.

[1] A. Kumar et al., Phys. Rev. D 106, 034505 (2022).
[2] A. Majumder, Phys. Rev. C87 034905 (2013).

Sprecher: Johannes Heinrich Weber (Humboldt-University of Berlin)

Computing_Jet_Transport_Coefficients_On_The_Lattice.pdf

14:20 Exploring jet transport coefficients by elastic and radiative scatterings in the strongly interacting quark-gluon plasma

We study the interaction of leading jet partons in a strongly interacting quark-gluon plasma (sQGP) medium based on the effective dynamical quasi-particle model (DQPM). The DQPM describes the non-perturbative nature of the sQGP at finite temperature $T$ and baryon chemical potential $\mu_B$ based on a propagator representation of massive off-shell partons whose properties are adjusted to reproduce the lQCD EoS for the QGP in thermodynamic equilibrium. We present the results for the jet transport coefficients, i.e. the transverse momentum transfer squared per unit length $\hat{q}$ and the energy loss per unit length $\Delta E =dE/dx$ in the QGP and investigate their dependence on the temperature $T$ and baryon chemical potential $\mu_B$ as well as on jet properties such as the leading jet parton momentum, mass, flavor, and the choice of the strong coupling constant. In this work both elastic and radiative scattering processes of leading jet parton with the sQGP partons are considered. We compute the cross sections and transport coefficients and compare the contributions from elastic partonic scattering and radiative processes for the emission of massive gluons. We present a comparison of our results for the elastic energy loss in the sQGP medium with pQCD results as well as with lattice QCD and also with estimates for $\hat q$ by the JET and JETSCAPE Collaborations based on a comparison of hydrodynamical calculations with experimental heavy-ion data.

Sprecher: Ilia Grishmanovskii (ITP, Frankfurt)

Grishmanovskii_HP23.pdf

14:40 From perturbative to non-perturbative QCD emissions with jets

In this work, by exploiting jet substructure techniques, we identify the transition from early-time perturbative splittings to late-time non-perturbative emissions and its associated timescale at both RHIC and LHC energies. We introduce three experimentally robust splittings along the jet clustering tree, each related to the perturbative, non-perturbative-like regions and the transition between them. The population of such splittings is quantified via a first phenomenological study of the formation time in a Monte Carlo model to highlight its sensitivities and discuss its experimental feasibility. Finally, we show how these timescales change in a scenario when jet quenching effects, induced by an extended Quark-Gluon Plasma, take place along the parton shower.

Sprecher: Raghav Kunnawalkam Elayavalli (Vanderbilt University)

pQCDtonpQCD_jets_rke_HP_March2023.pdf

15:00 Measurements of the azimuthal anisotropy of jets and high-$p_{\mathrm{T}}$ charged particles in Pb+Pb collisions with the ATLAS detector

The heavy-ion collisions produce a hot, dense medium, and high-momentum partons from the collision traverse this medium while losing energy to it. This talk presents new measurements of the azimuthal dependence with respect to the event plane of single jet yields and high momentum charged particles yields in Pb+Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV. As the distance traversed by the partons in the medium is dependent on the angle with respect to the event plane at which the partons are produced, these measurements give insight into the path-length dependence of parton energy loss. The magnitude of angular modulation is quantified by the parameter $v_n$ with respect to the $n^{th}$ order event plane. In this talk we will present these two measurements that show $v_2$, $v_3$, and $v_4$ as a function of $p_T$ and collision centrality. In both measurements, a non-zero value of $v_2$ and $v_3$ are observed, suggesting that fluctuations in the initial state play a small but distinct role in jet energy loss. Both measurements explore a higher transverse momentum regime and higher-order harmonics than current measurements benefiting from the high statistics 2018 Pb+Pb heavy ion data recorded by ATLAS. These measurements provide new information about the path-length dependence of jet quenching.

Sprecher: Xiaoning Wang (University of Illinois Urbana-Champaign)

HP20230328.pdf

15:20 Efficient description of medium response to jet energy loss

The injection of energy and momentum from a jet into the QGP generates a wake, which leads to soft and semi-hard particle creation correlated with the jet direction after the QGP hadronizes. As several jet quenching studies have shown, this medium response phenomenon plays a crucial role in our understanding of many jet structure and substructure observables. Nevertheless, a detailed account of the phenomenological consequences of those wakes is still lacking, partly because of the computational complexity of current techniques used to describe their properties. In this work we present a computationally efficient description of the event-by-event, jet-by-jet, determination of the properties of the hadrons coming from QGP wakes. By making use of a single set of universal solutions obtained within linearized hydrodynamics on top of a Bjorken flow, and performing the adequate set of scalings, translations, rotations and boosts, we are able to match the results obtained (with much greater computational cost) using 3+1D hydrodynamics.

Sprecher: Prof. Jorge Casalderrey-Solana (Universitat de Barcelona)

jcs_hp23.pdf

15:40 Measurements of Baryon-to-Meson Ratios in Jets in Au+Au and p+p Collisions at sqrt{s_{NN}} = 200 GeV by STAR

Measurements at RHIC and the LHC show strongly enhanced baryon-to-meson yield ratios at intermediate transverse momenta ($p_{T}$) in high-energy nuclear collisions compared to $p$+$p$ baseline. This enhancement is attributed to the following QGP effects: strong hydrodynamic flow and parton recombination. Jet probes have been used extensively to gain insights into QGP properties, with substantial modifications to jet yields and internal structures seen across multiple measurements. Despite apparent medium-induced changes to jet fragmentation patterns, LHC results indicate that in-jet particle production is significantly different from that of the QGP bulk. To explore this behavior at RHIC, we employ particle identification through time of flight and $dE/dx$ information alongside jet-track correlations to measure in-jet particle production for $p_{T} < 5.0$ GeV/c. We present the first in-cone baryon-to-meson yield ratios associated with fully reconstructed jets from 200 GeV Au+Au and $p$+$p$ collisions using the STAR detector at RHIC.

Sprecher: GABRIEL DALE-GAU (University of Illinois at Chicago)

HP2023_GDG_final_v9.pdf

16:00 → 16:30 Coffee break

16:30 → 18:10 Parallel: Electromagnetic & Electroweak Probes

Sitzungsleiter: Charles Gale (McGill University)

16:30 Using direct γ production to disentangle contributions from centrality biases and final state effects to high pt π0 production in d+Au collisions at 200 GeV.

PHENIX presents the simultaneous measurement of high pt (8-18 GeV/c) direct γ and π0 production in d+Au collisions at 200 GeV. The analysis is performed for different events samples selected by event activity. The direct γ-to-π0 ratio is independent of event activity, except for events with the highest activity where the ratio is slightly enhanced. Final state effects are expected to be small for direct photons and initial state effects are expected to be similar for direct γ and π0. Therefore, the new PHENIX results suggest that π0 production is suppression in the final state of the most central d+Au collisions. Expressed as nuclear modification factor RxA, this suppression is about 20%. Here RxA is determined in a model independent way, by quantifying the effective number of binary collisions from the ratio of direct photons measured in d+Au compared to p+p collisions. To establish if the suppression is linked to energy loss, PHENIX is currently analyzing p+Au and 3He+Au collisions. In this talk the latest results will be presented.

Sprecher: Axel Drees (Stony Brook University)

Drees-HardProbes-2023.pdf

16:50 BSM physics using photon-photon fusion processes in UPC in Pb+Pb collisions with the ATLAS detector

Relativistic heavy-ion beams at the LHC are accompanied by a large flux of equivalent photons, leading to multiple photon-induced processes. This talk presents searches for physics beyond the standard model enabled by photon-photon processes in both di-tau and di-photon final states. The tau-pair production measurements can constrain the tau lepton’s anomalous magnetic dipole moment (g-2), and a recent ATLAS measurement using muonic decays of tau leptons in association with electrons and tracks provides one of the most stringent limits available to date. Similarly, light-by-light scattering proceeds via loop diagrams, which can contain particles not yet directly observed. Thus, high statistics measurements of light-by-light scattering shown in this talk provide a precise and unique opportunity to investigate extensions of the Standard Model, such as the presence of axion-like particles.

Sprecher: Agnieszka Ogrodnik (Prague CU)

BSMinUPC_ATLAS_HP2023.pdf

17:10 Thermal photon measurements at PHENIX

Photons are emitted at all stages of relativistic heavy-ion collisions and do not interact with the medium strongly. With access to the versatility of RHIC, measurements of low momentum direct photons are made possible across different system size and beam energies. An excess of direct photons, above prompt photon production from hard scattering processes, is observed for a system size corresponding to $dN_{ch}/d\eta$ of 20-30, with a large azimuthal anisotropy and a characteristic dependence on collision centrality. After subtracting the prompt photon component, the inverse slope of the spectrum is continuously increasing with the effective temperature ranging from 250 MeV/c at $p_T$ of 1-2 GeV/c to about 400 MeV/c at 2-4 GeV/c. Within the experimental uncertainty, there is no indication of a system size dependence of the inverse slope. In this talk, results from Au+Au collisions from the PHENIX experiment will be presented.

Sprecher: Roli Esha (Stony Brook University)

hp2023.pdf

17:30 Electroweak-boson measurements from small to large collision systems with ALICE at the LHC

Electroweak bosons produced in hard-scattering processes at the early stage of the collision, are efficient probes of the initial state of the collision. While the W measurements in pp collisions are a stringent test of perturbative QCD-based calculations and production mechanisms, they can constrain the nuclear parton distribution functions in p-Pb and Pb-Pb collisions.

Electroweak bosons are studied with ALICE in pp collisions at $\sqrt s$ = 13 TeV, p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 8.16 TeV and Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV via their leptonic decays in the muon and electron channels at forward rapidity ($-4.0< \eta < -2.5$) and midrapidity ($\vert \eta \vert < 0.8$), respectively. The observations in p-Pb and Pb-Pb collisions at forward rapidity give access to low Bjorken-$x$ values, a phase-space region poorly constrained by heavy-ion experiments.

The latest W-boson results concerning differential measurements of the normalised production yields, production cross sections, nuclear modification factors and lepton-charge asymmetry as a function of rapidity, transverse momentum, collision centrality and charged-particle multiplicity are presented. The production of W bosons in association with hadrons as a function of the charged-particle multiplicity in pp collisions is reported as well. Comparisons with model calculations are discussed.

Sprecher: Shingo Sakai (Univ. of Tsukuba)

HP_W_ssakai.pdf

17:50 Thermal photon production rate from Transverse-Longitudinal(T-L) mesonic correlator on the lattice.

Thermal photons are vital tool to study Quark-Gluon Plasma The photon production rate from the plasma at some temperature T is proportional to the transverse spectral function $\rho_T(\omega=|\vec k|,\vec k)$. One can calculate the photon production rate also from the difference between $\rho_T(\omega,\vec k)$ (transverse) and $\rho_L(\omega,\vec k)$ (longitudinal) correlator as $\rho_L$ vanishes at the light cone. The UV part of $\rho_T-\rho_L$ is suppressed; therefore, the corresponding Euclidean correlator receives most of its contribution from the IR part of $\rho_T-\rho_L$. We also calculate the T-L correlator on $N_f=2+1$ flavor HISQ configurations with $m_l=m_s/5$ at temperature ∼1.15$T_c$ and 1.3 $T_c$. We have used two ansätze of the spectral function, which are 1) Polynomial ansatz of the spectral function connected to the UV region compatible with OPE expansion and 2) Hydro-inspired spectral function. We have also used the Backus-Gilbert method to estimate the spectral function. We will compare the photon production rate estimated from all these different methods.

Sprecher: Dibyendu Bala (Bielefeld University), Sajid Ali (Bielefeld University)

HP_2023_Latt_photon.pdf

16:30 → 18:10 Parallel: Heavy Flavours & Quarkonia

Sitzungsleiter: Peter Braun-Munzinger (EMMI/GSI - Helmholtzzentrum fur Schwerionenforschung GmbH (DE))

16:30 Comparison of Heavy quark Hadronization Mechanisms in heavy ion collisions

The hadronization process is a well-known non-perturbative process, which is happening in both elementary collisions such as $p+p$, $e^++e^-$ collisions, and also the relativistic heavy ion collisions. Studying the hadronization mechanism is crucial for understanding the QCD in low-energy regions.
In elementary collisions, the hadronization process is usually described by the fragmentation model, while the recombination plays an important role in quark hadronization in the hot medium, which created in relativistic heavy ion collisions. The state-of-art is mixing the fragmentation and recombination process. The recombination dominates in the low transverse momentum region while fragmentation takes over in the high transverse momentum region.
Due to the large mass, distinguishable, and traceable properties, heavy flavor supplies a unique probe to study the hadronization mechanism in heavy ion collisions.
We convened many theoretical groups to do the comparison of the hadronization models with given initial condition.
In this talk, we will present the differences and connections between different hadronization models.
We compare in detail the $H_{AA}$ yield and the elliptic flow $v_2$ of heavy flavor hadrons obtained in different theoretical models and point out how the different models influence the spectra. A summary will be given at the end of this talk.

Sprecher: Jiaxing Zhao (SUBATECH)

Jxzhao_HP2023.pdf

16:50 New insights into heavy-quarks hadronisation with charm and beauty hadrons in hadronic collisions with ALICE

In this contribution, we present the new measurements of non-prompt $\mathrm{D}^+$ and $\mathrm{D_s}$ in pp collisions at $\sqrt{s}$ = 13 TeV. Together with the final measurements of non-prompt $\mathrm{D}^0$ and $\Lambda_\mathrm{c}^+$, they are crucial to study the beauty quark hadronisation in proton-proton (pp) collisions and their difference with respect to $\mathrm{e^+e^-}$ collisions. In addition, the baryon-to-meson ratio in pp collisions compared with that in $\mathrm{e^+e^-}$ and electron--proton collisions and model predictions, and the measurements of charm fragmentation fraction in pp and pPb collision will be reported as well.

Furthermore, the new non-prompt $\Lambda_\mathrm{c}^+/\mathrm{D}^0$ ratio in p-Pb collisions as well as the first measurement of non-prompt $\mathrm{D}^0$ nuclear modification factor $R_\mathrm{pPb}$ at $\sqrt{s_\mathrm{NN}}=5.02$ TeV will be presented. The status of prompt $\Xi_\mathrm{c}$ $R_\mathrm{pPb}$ studies will be reported. They provide important information about Cold-Nuclear Matter (CNM) effects and to understand how the possible presence of collective effects could modify the production of heavy-flavour hadrons and the similarities observed among pp, p-nucleus, and nucleus--nucleus systems.

Sprecher: Annalena Kalteyer

HP23_HFHadronization_ALICE_Kalteyer.pdf

17:10 Modification of heavy quark hadronization in high-multiplicity collisions

The total rate of heavy quark production can be calculated with perturbative QCD techniques. However, the fraction of heavy quarks that pair with a light quark (forming mesons) versus the fractions combine with two other quarks (baryons) baryons or 3 or more other quarks (exotic states) is sensitive to the nonperturbative hadronization process. LHCb is uniquely well suited to study such effects in the heavy quark sector, down to very low transverse momentum. Here we will present LHCb results on the production rates of $\Lambda_b^{0}$ baryons and $B_{s}^{0}$ mesons relative to $B^{0}$ mesons, and $D_{s}^{+}$ relative to $D^{+}$ mesons versus multiplicity in $pp$ and $p$Pb collisions. Potential implications for the hadronization mechanism of heavy quarks and our understanding of the factorization of fragmentation functions will be discussed.

Sprecher: chenxi gu (Laboratoire Leprince-Ringuet, École Polytechnique, CNRS)

ChenxiGu_HP2023.pdf

17:30 Search of hot QCD effects via dynamics and productions of heavy flavor quarks in small systems with CMS detector

The surprising collectivity signal emerging in small hadronic systems for light and heavy quarks raises the question whether a quark-gluon plasma is created in those systems too. The conjectured QGP formation could also enhance baryon production because of coalescence processes. Moreover, strangeness enhancement signals have been observed. Recent measurements show charm baryon-to-meson ratios are enhanced in heavy ion collisions compared to pp collisions. In this talk, the studies of collectivity for charm and bottom mesons in pp and pPb collisions will be presented. New measurements of the multiplicity dependence of charm baryon-to-meson ratios will also be presented over a wide multiplicity range, and compared with those in the strangeness sector. These measurements provide new insights into the origin of heavy flavor hadron collectivity and charm hadronization.

Sprecher: Yousen Zhang

yousen_HardProbe2023_v5.pdf

16:30 → 18:10 Parallel: High-Momentum Hadrons & Correlations

Sitzungsleiter: William Horowitz (University of Cape Town)

16:30 A multi-messenger Bayesian Inference analysis of QGP jet transport using inclusive hadron and reconstructed jet data by JETSCAPE

The JETSCAPE Collaboration reports a new Bayesian Inference analysis of jet transport in the QGP, using both hadron and jet inclusive suppression data. The JETSCAPE framework comprises a modular multi-stage modeling of in-medium jet evolution and medium response, together with a statistical framework for rigorous data-model comparison using a Bayesian formalism. The multi-stage approach includes virtuality-dependent in-medium partonic energy loss coupled to a detailed dynamical model of QGP evolution. In this talk we present a new JETSCAPE Bayesian inference analysis that extends the previously published JETSCAPE Bayesian determination of $\hat{q}$, which was based solely on inclusive hadron suppression data. It now incorporates inclusive jet measurements at RHIC and the LHC as well. We explore tension between different datasets considered in the analysis, and report a new, multi-messenger, determination of $\hat{q}$. This study represents the next step in the program toward a comprehensive study of the constraints of the QGP properties from jet quenching data. Future possibilities, including more sophisticated modeling and the inclusion of other types of measurements, will also be discussed.

Sprecher: Frau Yi Chen (MIT)

20230328_HardBayesianResult_HardProbes2023_YiChen_v15.pdf

16:50 Study on the energy loss of light and heavy quarks in QGP at PHENIX

In studies of the QGP, it has been observed that in high-energy heavy-ion (A+A) collisions, high-momentum hadrons and heavy flavor electrons are suppressed, indicating that QGP is strongly coupled, and that quarks lose energy as they traverse the medium. In order to quantitatively discuss this important energy loss mechanism, for charged hadrons consisting of light quarks, in addition to the conventional fractional momentum losses (Sloss), which uses the comparison with p+p, the angle-dependent fractional momentum losses (S'loss) at different emission angles using azimuthal anisotropy ($v_2$) are measured at $\sqrt{{s}_{NN}}$ = 200 GeV. We will report the detailed and new path-length dependent functions obtained from these measurements.
We will also discuss the latest heavy quark measurements in PHENIX for a comprehensive understanding of the energy loss mechanism. Like light quarks, heavy quarks lose energy when interacting with the QGP. The gluon bremsstrahlung by heavy quarks is expected to be suppressed at small angles due to the dead cone effect, and thus the energy loss is expected to be quark-mass-dependent. PHENIX silicon detectors are able to separate single electrons from charm and bottom decays by utilizing the difference of their decay lengths. In this talk, we will report the latest results of heavy flavor productions and their nuclear modifications as a function of $p_T$ and centrality, and discuss the energy loss mechanisms in QGP.

Sprecher: Dr. maya shimomura (Nara Women's University)

HP2023_energyloss_MIP_maya_v4.pdf

17:10 Measurement of the deuteron coalescence probability in jets with ALICE

The microscopic production mechanism of light (anti)nuclei in high-energy hadronic collisions is still mysterious and is a highly debated topic in the scientific community. Two different phenomenological models are typically used to describe the experimental data: the statistical hadronization model and baryon coalescence. In the former, light nuclei are emitted from a source in local thermal and hadrochemical equilibrium. Their yields are calculated using the QCD partition function by imposing the conservation of quantum numbers inside the so-called correlation volume. In the coalescence approach, light nuclei can be formed if the phase-space configuration of nucleons at kinetic freezeout is compatible with the Wigner density of the bound state. A straightforward prediction of the coalescence model is an enhanced coalescence probability of nuclei inside jets compared to that in the underlying event, measured in small collision systems.

In this contribution, the $p_{\rm T}$-differential production yields and coalescence probabilities of (anti)deuterons inside jets and in the underlying event measured by ALICE in small collision systems are presented. These results are compared to expectations from coalescence and a reaction-based model. In the latter approach, implemented in the PYTHIA 8.3 event generator, deuterons are generated using ordinary nuclear reactions.

Sprecher: Marika Rasà (University and INFN Catania)

HardProbes2023_Rasa.pdf

17:30 Strangeness production in jets and underlying event in p-Pb and pp collisions measured with ALICE

Two-particle jet-like angular correlations with identified strange hadrons allow the measurements of both jet and non-jet components of strange particle production, and in this way to investigate the extent to which the strangeness enhancement observed in small collision systems is a result of soft (medium-like) or hard (jet-like) processes. Relative contributions of these processes to strangeness production mechanisms can be probed by examining changes in the strange hadron over non-strange hadron ratios within jets and in the underlying event separately. In addition, changes to the jet hadrochemistry are studied by measuring strangeness production in the away-side jet.

In this talk, we present the first measurements of the $\phi$/h, $(\Lambda+\overline{\Lambda})$/h and $\mathrm{K_{S}^0}$/($\pi^++\pi^-$), $(\Lambda+\overline{\Lambda})$/($\pi^++\pi^-$) ratios in jets and underlying event as a function of charged-particle multiplicity using jet-like di-hadron angular correlations in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$= 5.02 TeV and pp collisions at $\sqrt{s}$= 13 TeV measured with ALICE. The results suggest that the strangeness enhancement originates in the underlying event.

Sprecher: Ryan Hannigan (CERN)

hardprobes_20230328.pdf

17:50 A multistage framework for studying the evolution of jets and high-pT probes in small collisions systems

Understanding the modification of jets and high-$p_T$ probes in small systems requires the integration of soft and hard physics. We present recent developments in extending the JETSCAPE framework to build an event generator, which includes correlations between soft and hard partons, to study jet observables in small systems. The multi-scale physics of the collision is separated into different stages. Hard scatterings are first sampled at binary collision positions provided by the Glauber geometry. They are then propagated backward in space-time following an initial-state shower to obtain the initiating partons’ energies and momenta before the collision. These energies and momenta are then subtracted from the incoming colliding nucleons for soft-particle production, modeled by the 3D-Glauber + hydrodynamics + hadronic transport framework.This new hybrid approach includes non-trivial correlations between jet and soft particle productions in small systems. We calibrate this framework with the measured event activity distributions in p+p and p+Pb collisions at 5.02 TeV. We further compare our results for final state hadron’s $p_T$-spectra from low to high $p_T$ in p+p and p+Pb collisions with experimental results in p+Pb at the LHC. Lastly, we present results of additional observables such as the distributions of jet recoiling from a high-$p_T$ hadron and the nuclear modification factor $R_{pPb}$ as a function of event activity.

Sprecher: Abhijit Majumder (Wayne State University)

majumder-HP2023-small-systems.pdf

majumder-HP2023-small-systems.pptx

16:30 → 18:10 Parallel: Jets and their modification in QCD Matter

Sitzungsleiter: Shanshan Cao (Shandong University)

16:30 The information content of jet quenching and machine learning assisted observable design

We employ machine learning techniques to identify important features that distinguish jets produced in heavy-ion collisions from jets produced in proton-proton collisions [1]. We formulate the problem using binary classification and focus on leveraging machine learning in ways that inform theoretical calculations of jet modification: (i) we quantify the information content in terms of Infrared Collinear (IRC)-safety and in terms of hard vs. soft emissions, (ii) we identify optimally discriminating observables that are analytically tractable, and (iii) we assess the information loss due to the heavy-ion underlying event and background subtraction algorithms. We illustrate our methodology using Monte Carlo event generators, where we find that important information about jet quenching is contained not only in hard splittings but also in soft emissions and IRC-unsafe physics inside the jet. This information appears to be significantly reduced by the presence of the underlying event. We discuss the implications of this for the prospect of using jet quenching to extract properties of the QGP. Since the training labels are exactly known, this methodology can be used directly on experimental data without reliance on modeling. We outline a proposal for how such an experimental analysis can be carried out, and how it can guide future measurements.

[1] Lai, Mulligan, Ploskon, Ringer [JHEP 10 (2022) 011]

Sprecher: Mateusz Ploskon (Lawrence Berkeley National Laboratory)

MateuszPloskon_HP23.pdf

16:50 Measurement of the jet mass and angularities in Pb-Pb collisions at 5.02 TeV with ALICE

In recent years jet substructure observables have been used at the LHC as instruments to search for new physics and test perturbative and non-perturbative processes in QCD. In heavy-ion collisions, these jet substructure observables can additionally elucidate the production and evolution of the QCD medium. The jet mass is one such observable that probes the momentum transfer scale of the initial hard scattering. Additionally, the generalized jet angularities summarize the jet substructure using two continuous parameters which differentially weight the jet constituents’ relative angle and $p_\mathrm{T}$. One jet angularity configuration, the jet thrust, has been compared to the jet mass and has shown surprising differences in comparison with models. ALICE has performed a new measurement for both observables using an identical jet sample to study this difference more closely. The ALICE tracking system's high-precision capability provides a unique opportunity at LHC energies to measure jets at lower $p_\mathrm{T}$. We report the generalized jet mass and jet angularities using charged-particle tracks in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV with ALICE. Various jet angularity parameters are investigated for the jet resolution parameter R = 0.2. Results are compared to pp collisions and theoretical models.

Sprecher: Ezra Lesser (UC Berkeley)

2023-03-28 -- Measurement of the jet mass and angularities in Pb-Pb collisions at 5.02 TeV with ALICE.pdf

17:10 A New Model for Jet Energy Loss in Heavy Ion Collisions

We present a new model for jet quenching from coherent radiation in a brick medium. The jet energy loss is simulated as a perturbative final-state vacuum parton shower followed by a medium-induced shower originating from elastic and radiative collisions with the medium constituents. Coherency is achieved by starting with trial gluons that acts as field dressing of the initial jet parton. These are formed according to a Gunion-Bertsch seed. The QCD version of the LPM effect is attained by increasing the phase of the trial gluons through elastic scatterings with the medium. Above a phase threshold, the trial gluon will be realised and can produce coherent radiation themselves.

The model has been implemented in a Monte Carlo code and has been validated by successfully reproducing the BDMPS-Z prediction for the energy spectrum. The realistic case with minimal assumptions are also produced and shown. In particular, we show the influence of various parameters on the energy spectrum and transverse momentum distribution, such as the in-medium quark masses, the energy transfer in the recoil process, and the phase accumulation criteria, especially for low and intermediate energy gluons.

Future studies will allow for the interface with full simulations of the quark-gluon-plasma with hydrodynamic evolution, such as vHLLE, along with subsequent hadronisation of the jet partons in order to produce realistic distributions that can be directly compared to LHC and RHIC data.

Sprecher: Dr. Alexander Lind (Subatech, IMT Atlantique)

Lind_HardProbes2023.pdf

17:30 Measurement of the angle between jet axes and energy-energy correlators with ALICE

Modifications of the internal structure of jets through interactions with the QGP produced in heavy-ion collisions, referred to as jet quenching, are used to study the properties of the QGP. In this talk, we present the first measurement of the angle between pairs of jet axes, $\Delta R_{\rm axis}$, in central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV with ALICE. We compare this novel jet substructure measurement to a selection of jet quenching models. The data favor models implementing incoherent energy loss of jet constituents in the QGP, but also agree with models invoking an enhancement of quark-initiated jets. On the other hand, our measurement disfavors the intra-jet in-medium $p_\mathrm{T}$ broadening from the BDMPS formalism. Moreover, to comprehensively study the perturbative and non-perturbative aspects of jet structure, we measured the energy-energy correlators (EEC) that emphasize the angular structure of the energy flow within jets. Defined as the energy-weighted cross section of particle pairs inside jets, the scaling behavior of the EECs as a function of pair distance exposes a distinct separation of the perturbative from the non-perturbative regime, revealing parton-type dependent dynamics of jet formation and their confinement into hadrons. In this talk, we present a new measurement of EEC in pp collisions at the LHC and compare it with pQCD predictions. This measurement serves as a baseline for future measurements in heavy-ion collisions.

Sprecher: Reynier Cruz-Torres (Lawrence Berkeley National Lab)

230328_HP23_v3.pdf

18:15 → 20:30 Poster Session

18:15 $\pi^{+}\pi^{-}$ and $K^{+}K^{-}$ photoproduction in ultra-peripheral Pb--Pb collisions with ALICE

Ultra-peripheral collisions (UPC) of heavy nuclei provide the opportunity to study interactions between high energy photons induced from the electromagnetic field of ultrarelativistic nuclei and the nuclei from the other beam. The photon fluctuates to a quark-antiquark dipole which then elastically scatters off the nucleus, emerging as vector meson and opposite-charge pseudoscalar meson pair.

The excellent particle identification capabilities of ALICE enable the study of photoproduced $\pi^{+}\pi^{-}$ pairs and $K^{+}K^{-}$ pairs at midrapidity in Pb--Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV. We will present an analysis of the $\rho^{0}$ meson and direct $\pi^{+}\pi^{-}$ photoproduction exhibiting the interference, obtained from a fit to the invariant mass spectrum of $\pi^{+}\pi^{-}$ pairs. In addition, we will present the prospects of studying the photoproduction of direct $K^{+}K^{-}$ pairs in UPCs.

Sprecher: Minjung Kim (UC Berkeley)

18:15 $\rm{J/\psi}$ photoproduction and exclusive dimuon production in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$=8.16 TeV at the LHC with the ALICE experiment

Photonuclear interactions are studied in ultra-peripheral p-Pb collisions with the ALICE experiment, where the photon radiated by a Pb nucleus probes the gluon density of the proton at low Bjorken-x. The exclusive $\rm{J/\psi}$ photoproduction cross section $\rm{\sigma(\gamma + p \rightarrow J/\psi + p)}$ is expected to follow a power law trend as $x$ decreases, but it should deviate from this trend at low $x$ due to gluon saturation. In addition, gluon saturation effects are also expected to be visible when studying the dissociative $\rm{J/\psi}$ photoproduction cross section $\rm{\sigma(\gamma + p \rightarrow J/\psi + X)}$ because of reduced quantum fluctuations of the substructure of the proton in the saturation regime. The ALICE collaboration has measured both processes. In this talk, the first measurement of the dissociative $\rm{J/\psi}$ photoproduction at the LHC will be presented. Finally, we will present the study of dimuon events produced in two-photon interactions. First results for low-mass dimuons will be discussed. Such measurements complement the studies of $\rm{J/\psi}$ photoproduction and contribute to a better understanding of the photon fluxes generated by the lead nucleus.

Sprecher: Minjung Kim (UC Berkeley), Dr. Michael Winn (Irfu/CEA-Saclay)

18:15 Analytic and Semi-Analytic Results for Color Glass Condensate in the Weak-Field Limit

The classical field approximation to Color Glass Condensate for two colliding nuclei has been solved in the literature using numerical methods and recursive analytic solution. In the weak field limit, analytic solutions in transverse momentum space have also been known for some time. Based on the latter, we derive expressions for the space-time dependence of classical gluon 2-point functions $\langle F^{\mu\nu}(x^\alpha)F^{\kappa\lambda}(y^\beta)\rangle $ in the weak-field limit. For the McLerran-Venugopalan (MV) model, in many cases these expressions are shown to lead to solutions in closed analytic forms valid at all times. We also propose an alternative model which maintains UV-regularity by accounting for local correlations between color charges in the transverse plane. The new model allows for a straight forward calculation of the time dependence of the gluon energy momentum tensor and angular momentum density in early nuclear collisions in the weak field limit. We also discuss the initial motion of the nuclei after the collision.

Sprecher: Herr Stephen Robicheaux (Texas A&M University)

Robicheaux_Poster.pdf

18:15 Anisotropic flow and the valence quark skeleton of hadrons

We developed a formalism to study momentum anisotropy, in particular, the collective flow $v_2$, in the ultra-relativistic onium-onium scattering. We derived the impact-parameter dependent cross section up to the next-to-leading order in the eikonal approximation. With this formalism, we are able to interpret the origin and behavior of $v_2$ in the dilute limit, by investigating the elementary dipole-dipole scattering, $q\bar q+q\bar q\to g+X$. We calculated $v_2$ in the $\pi+\pi\to g+X$ process at a comprehensive coverage of impact parameter and transverse momentum. The valence sector light-front wave function of the $\pi$ is obtained numerically from the Basis Light-Front Quantization, a non-perturbative light-front Hamiltonian approach, in a holographic basis. For comparison and as a complementary study, we also calculated $v_2$ in the $J/\psi+J/\psi\to g+X$ process. The $J/\psi$ light-front wavefunction is built analytically from the phenomenological framework of Small-basis Light-Front Wavefunction. With this work, we have shown that momentum anisotropy can develop due to the interference of the valence quarks. This formalism is generic and can be applied to other hadrons and photons in the future.

Sprecher: Meijian Li (University of Santiago de Compostela), Prof. Hong Zhang (Shandong University)

poster_ppv2_HP2023_MeijianLi.pdf

18:15 Anisotropic quenching of heavy flavor in flowing matter

During the last years, there has been an increasing interest in how the quark mass affects the jet quenching phenomena and dynamics of heavy flavor in HIC. Here, we will present a new effect, which consists in anisotropic broadening and gluon radiation sourced by the background flow, transverse to the parton momentum, and sensitive to the quark mass. This effect appears due to a modification of the scattering potential in evolving matter, and scales as second power of mass over the parton energy. We will also discuss how this mass ordered anisotropy affects the overall heavy flavor directionality in HIC and its possible effect in the observed harmonic coefficients from the corresponding momentum anisotropy in both small and large systems.

Sprecher: Xoán Mayo López (Instituto Galego de Fïsica de Altas Enerxías - IGFAE)

18:15 Assessing QGP momentum scales with energy correlators

Correlation functions of energy flow operators have been recently proposed as a tool to identify the onset of colour coherence within the jets. As a promising exploration avenue to unveil the scales of the Quark-Gluon Plasma, it has yet to be demonstrated how the medium back-reaction to the jet propagation will blur such identification. In this work, by using a perturbative prescription to describe the jet-medium interactions and its re-scatterings, we show which weight of the normalised two-point correlator can maximise the separation between the wide range of momentum scales that go into the development of an in-medium jet: in-medium radiation and medium-recoiling particles. Additionally, we also explore the energy correlators' sensitivity to the different medium response momentum scales and their thermalization.

Sprecher: Raghav Kunnawalkam Elayavalli (Vanderbilt University)

18:15 Can Transverse Mass Scaling Shed Light on the Event-Activity Dependence of Y-Mesons Production at LHC?

Recent measurements by the CMS and ATLAS experiments reveal a deficit of charged particles in pp collisions with excited Υ(nS) states compared to the Υ(1S) ground state. This observation is suggested to be a manifestation of excited bottomonia suppression in pp interactions. The analysis presented in this talk is an independent approach, complementary to the CMS and ATLAS analyses, based on first physics principles that finds a significant suppression in the production of excited bottomonia states in pp collisions at the LHC energies. The analysis uses transverse mass scaling as an empirical tool to quantify the magnitude of the suppression. Based on the analysis of shapes of momentum distributions, one can conclude that the Y(2S) production in pp collisions is suppressed by a factor of approximately 1.6 and Υ(3S) by a factor of approximately 2.4 from what would be expected from the momentum distribution of Y(1S). Details of the analysis and striking parallels to the findings of ATLAS and CMS experiments would help shed light on the nature of quarkonia production in pp collisions.

Based on https://arxiv.org/abs/2203.11831

Sprecher: Alexander Milov (Weizmann Institute of Science), Zvi Citron (The Ben Gurion University of the Negev)

sasha_misbT_2022_09_26.pdf

18:15 Charm Meson Production in Relativistic Heavy-Ions Collisions in the context of Non-Extensive Statistics

This project aims the application of non-extensive statistics, more specifically that proposed by C. Tsallis, in the study of the transverse momentum distribution of mesons composed of charm quarks produced in collisions between heavy ions at relativistic energies. Non-extensive statistics has been very successful in the description of transverse momentum spectra of particles produced in hadronic collisions at high energies, whose interpretation of the non-extensive parameter q has been widely discussed. The success of this description might be connected to the degree of equilibrium reached in these collisions, an important condition for a broad understanding of its dynamics. This question is particularly important for heavy quarks in collisions between heavy ions, given its unique character in the investigation of the medium formed in these collisions. We will present some results of a systematic study of charm meson transverse momentum distributions fits, mainly the relative behavior of the temperature and q parameter for different particles and collision centralities, searching for an interpretation for the obtained results regarding the dynamics of charm quarks in these collisions.

Sprecher: Marcelo Munhoz (Universidade de São Paulo)

18:15 Collectivity at LHCb

Particle correlations are a powerful tool to study the bulk properties in relativistic heavy ion collisions. The momentum correlations between identical particles originating from the same particle-emitting source, referred to as the Bose-Einstein correlations, measure scales that are related to the geometrical size of the source. The two particle azimuthal angular correlations measure the momentum spatial anisotropy of produced particles, providing information on collective phenomena arising in the dense nuclear medium. This poster will discuss new LHCb measurements of Bose-Einstein correlations and collective flow coefficients in $p$Pb and PbPb collisions in the forward rapidity region.

Sprecher: Mateusz Goncerz

LHCb_BEC_poster.pdf

18:15 Data-driven quark and gluon jet modification

Distinguishing between the modification of quark- and gluon-initiated jets in the quark-gluon plasma (QGP) remains an unresolved challenge without a definitive answer from experiment. We demonstrate that a fully data-driven technique, known as topic modeling, may be used to study the separate modification of quark and gluon jets experimentally. Our proof-of-concept study is based on proton-proton and heavy-ion collision events from the Pyquen generator with statistics accessible in Run 4 of the Large Hadron Collider. We use topic modeling to extract the separate modification of quark and gluon jet substructure in the QGP. We show that this data-driven technique is robust to large backgrounds in heavy-ion collisions by smearing our input distributions and obtaining similar results. These results suggest the potential for an experimental determination of quark and gluon jet substructure and their modification.

Sprecher: Dr. Jasmine Brewer (CERN)

18:15 Dijet probes of the initial state in p+Pb collisions with ATLAS

The measurement of the dijet production cross-section in p+Pb collisions is of great interest to the understanding of initial state effects. The analysis of this channel can provide input to the parameterization of the modification of parton distribution functions (PDFs) in nuclei and to search for the onset of non-linear QCD effects or gluon saturation at low Bjorken-x. In 2016, the ATLAS experiment at the LHC collected 164 nb$^{-1}$ of data from p+Pb collisions at the center-of-mass energy of 8.16 TeV. This poster presents ATLAS preliminary results for the triple-differential inclusive dijet cross-section in p+Pb. The results of this measurement can be used to constrain nuclear PDFs over a broad kinematic range. The events characterized by at least one jet in the forward region are also analyzed as a function of centrality to compare the dijet production in central and peripheral collisions and search for evidence of gluon saturation.

Sprecher: Aric Tate

HP2023_Tate.pdf

18:15 Dilepton anisotropy at low beam energies in a transport approach

We present calculations of dielectron anisotropic flow in heavy-ion collisions at HADES beam energies from a hadronic transport approach. The collectivity of the electromagnetic radiation produced during the evolution of these collisions has recently been dubbed as a barometer, serving as a probe for the flow velocity of the underlying hadronic matter. In particular, we study the elliptic flow coefficient $v_2$ of dileptons in different collisions systems, and its relation to the flow of hadrons.

Sprecher: Renan Hirayama (FIAS)

Poster_HirayamaRenan_final.pdf

18:15 Disentangle effects from the initial stage and the evolution stage in heavy ion collisions using EPOS and PHSD

Keywords : Heavy-ion Collisions, Event generator, EPOS, PHSD, EPOSi+PHSDe, Quark-Gluon
Plasma

Ultrarelativistic heavy-ion collisions at RHIC and the LHC provide a hot and ultra-dense form of matter composed of deconfined quarks and gluons, named QGP. Different models like EPOS and PHSD allow to study the space-time evolution of such heavy-ion collisions. Their dynamics is complicated; hence, various stages should be considered. The first is the primary scattering which defines to a large extent the matter distribution in the phase-space. The second stage concerns the evolution of the partonic system until the system is sufficiently dilute to hadronize. The EPOSi+PHSDe approach is introduced in this thesis, in which the EPOS model is used to determine the initial distribution of matter (partons/hadrons). This part is referred to as EPOSi. Then PHSD is employed to simulate the evolution of the matter in a non-equilibrium transport approach, referred to as PHSDe. The coupling of the two approaches is non-trivial and not straight-forward. Comparing the three models, EPOS, EPOSi+PHSDe, and PHSD, interesting results find concerning their respective space-time evolutions. The results demonstrate considerably different behavior in terms of radial expansion, especially asymmetric expansion, indicating that these three models will provide different results concerning key observables ( pT/mT spectra, y/ƞ distribution, v2/3/4) for Au-Au collisions at 200 GeV/A.

Sprecher: Frau Mahbobeh Jafarpour (Subatech)

HP2023_poster.pdf

18:15 Electromagnetic fields evolution and heavy flavor probes in relativistic heavy ion collisions

The electromagnetic fields produced by non-central heavy ion collisions are extremely powerful and give rise to a plethora of fascinating subjects in the strongly interacting matter. Their evolution is a significant and unresolved issue.
In this talk, firstly, I will show the electromagnetic evolution in the pre-equilibrium stages which is a gluon-dominated and far-from-equilibrium system after the collisions. Quarks and antiquarks will be produced gradually via inelastic collisions. We find the induced magnetic field is very weak in this stage due to the lacking of quarks.
Next, I will present the new effect we proposed which is called the incomplete electromagnetic response of hot QCD matter.
We examine the validity of Ohm's law and find that the induced electric current increases from zero and relaxes towards the value from Ohm's law. The lower-than-expected electric current significantly suppresses the induced magnetic field and makes the electromagnetic response incomplete. And leads to a strong suppression of the magnetic field.
Considering both these two effects, the magnetic field will decay faster in heavy ion collisions, and which magnitude is much weaker than expected.
Finally, I will show our study on the charmonium dissociation under electromagnetic fields, which can be a sensitive probe for detecting the short-lived electromagnetic fields in heavy-ion collisions.

Sprecher: Jiaxing Zhao (SUBATECH)

18:15 Evolution of initial state fluctuations in the hotspot model

The hotspot model has proven to be an efficient tool to study coherent and incoherent diffraction HERA data by modelling the initial state fluctuations of the gluon density of the proton. The hotspot model in its original form is a non-perturbative model applicable for low momentum transfer and underestimates the incoherent cross section in orders of magnitude when extended for large momentum transfer studies for J/ψ photo-production at HERA. We present here a model of hotspot splittings based on the resolution for the evolution of initial state fluctuations in the hotspot model inspired by the DGLAP parton shower approach This is reliable as both the Bjorken limit and the incoherent diffraction at large momentum transfer probes the gluon wave function at smaller length scales as we increase the resolution. In addition to the geometrical fluctuations, we have additional sources of fluctuations in our model namely the hotspot width, number, and normalisation fluctuations which leads to a good agreement of our model’s prediction with data. In the framework developed, we obtain a good description of both the normalization and shape of coherent and incoherent differential cross sections (t-spectrum) simultaneously.

Sprecher: Arjun Kumar (Indian Institute of Technology Delhi)

Poster_HardProbes_final.pdf

18:15 Exploring the impact of jet substructure observables on the Bayesian inference of medium properties

Bayesian inference provides a powerful approach to constrain jet quenching model parameters using experimental measurements. It remains an open question, however, which jet observables provide complementary information in this approach, and in turn which observables the community should focus on measuring and calculating. In this talk we report a first, exploratory study which incorporates jet substructure observables in a Bayesian inference analysis of jet quenching, based on the JETSCAPE framework. We examine the additional information that jet substructure observables provide beyond that contained in inclusive jet and hadron suppression observables. We discuss the implications of these findings on the future experimental and theoretical jet quenching programs, including both opportunities and limitations offered by jet substructure observables.

Sprecher: Dr. Peter Jacobs (LBNL)

18:15 Exploring transverse momentum broadening in expanding medium induced cascades

In this work, we assess the impact of the expansion of the medium on angular distribution of gluons at different kinematical scales in a medium-induced cascade . Firstly, we study the scaling of the gluon spectra at low$-x$ between expanding and static medium profiles and apply them to obtain the transverse momentum broadened spectra. The numerical solutions for the in-medium cascades are obtained from the gluon evolution equations using the Monte Carlo event generator MINCAS. Additionally, we investigate the early and late onset of the initial quenching time for the Bjorken expanding profile. Next, we study the angular distributions for the in-cone radiation for different media and observe that the out-of-cone energy loss proceeds via the radiative break-up of hard fragments followed by an angular broadening of soft fragments. We note that for an effective in-medium path length, the angular distributions for soft fragments are very similar for different media. Also, harder jet fragments within the jets inside a cone are more sensitive to the details of the medium expansion as compared to softer fragments which are responsible for most of the gluon multiplicity in the cascade. Finally, we observe that cascades in the expanding media are relatively more collimated than in a static media and discuss phenomenological implications of our results on jet quenching observables.

Sprecher: Souvik Priyam Adhya (IFJ-PAN, Krakow, Poland)

hp23_poster_souvik_v2.pdf

18:15 Extended hydrodynamics regime and jet-medium interaction

In the context of jet-medium interaction, we consider the response of QCD-like plasma to energy/momentum disturbance as a function of the gradient. For both N=4 super-Yang Mills theory in strong coupling limit and kinetic theory under relaxation time approximation, we find that hydrodynamic modes continue dominating medium's response even in the region where Knudsen number is large. However, in this extended hydrodynamic regime, both the first-order and second-order hydrodynamics fail to characterize medium's behavior. We construct a simple yet not trivial extension of the Muller-Israel-Stewart theory, namely MIS, and show this novel framework can quantitatively describe hydrodynamic modes in both hydrodynamic and extended hydrodynamic regimes with a suitable choice of model parameters for representative microscopic theories with and without quasi-particle descriptions.We apply MIS to study how a Bjorken-expanding QGP responds to a moving energetic parton.

[1] Weiyao Ke and Yi Yin, 2208.01046 .

Sprecher: Yi Yin (Institute of Modern physics (CAS), China)

EHR_HP_YiYin_inpdf.pdf

18:15 Femtoscopic correlations of D0 mesons with identified hadrons in Au-Au collisions at sqrt{s_{{NN}} = 200 GeV at STAR

Heavy quarks, like charm quarks, are produced early in the relativistic heavy-ion collisions and probe all stages of the evolution of the created medium – the Quark Gluons Plasma. Two-particle correlations at low relative momentum (the femtoscopic correlations) are sensitive to the interactions in the final state and the extent of the region from which correlated particles are emitted (so-called region of homogeneity). A study of such correlations between charmed mesons and identified hadrons could shed light on their interactions in the hadronic phase and interaction of charm quarks with the bulk partons.

We will present a study of femtoscopic correlations of $D^{0}$-$\pi$, $D^{0}$-$K$, $D^{0}$-proton pairs at mid-rapidity in Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV using data taken in the year 2014 by the STAR experiment. $D^{0}$ mesons are reconstructed via the $K^{-}$-$\pi^{+}$ decay channel using topological criteria enabled by the excellent track pointing resolution provided by the Heavy Flavor Tracker. We will present the femtoscopic correlation function for $D^{0}$ transverse momentum $p_{\rm T}>1$ GeV/c in the 0-80% centrality.

Sprecher: Priyanka Roy Chowdhury (Warsaw University of Technology)

HP2023_poster_v8.pdf

18:15 First performance results from upgraded LHCb and SMOG II

The LHCb experiment has recently undergone a series of major upgrades: the entire tracking system has been replaced with higher-granularity sensors, the readout electronics have been upgraded, and all hardware triggers have been replaced with a new state-of-the-art streaming readout system. In addition, the gaseous target SMOG system has been upgraded with a dedicated storage cell to greatly increase the rate of fixed target collisions at LHCb. This talk will include the first performance results from the new LHCb tracking system, the streaming readout system, and SMOG II, with a focus on how these upgrades directly impact the LHCb heavy ion physics program. Further upgrades planned for LHC Run 4 and 5 will also be discussed.

Sprecher: Chiara Lucarelli

HP23_poster_v2.pdf

18:15 First results of dielectron analyses with ALICE in Run 3

The ALICE experiment has been upgraded over the last years during the LHC Long Shutdown 2.
With the new and upgraded detectors ALICE is now capable of reading out the data of the collisions in a continuous way. With a data acquisition rate 100 times larger than before, an integrated luminosity of more than 10 nb$^{-1}$ is expected to be collected for Pb--Pb collisions during the Run 3 (2022-2025) and Run 4 (2029-2032) data taking periods. In these heavy-ion collisions, we produce a quark-gluon plasma which radiates virtual thermal photons which mainly decay into dielectrons (electron-positron pairs).
Since dielectrons do not interact strongly, they are excellent probes of the hot, strongly-interacting matter produced in heavy-ion collisions. Not only the improved readout of the detectors but also the reduced material budget, as well as the improved pointing resolution of the detectors, are crucial for the dielectron analysis. They will help controlling the background from photon conversions and heavy-flavor hadron decays within the dielectron spectra.

This poster will give an overview of the first performance studies for dielectron analyses with the ALICE experiment based on Run 3 data. It will summarize the techniques used to track, identify and select electrons and positrons. Furthermore, first results of the dielectron spectra and their corresponding signal-to-background ratios and significances will be presented together with a comparison to the results in Run 2.

Sprecher: Florian Eisenhut

18:15 Flow and transverse momentum fluctuations in Pb+Pb and Xe+Xe collisions with ATLAS: assessing the initial condition of the QGP

Constraining the initial condition of the QGP using experimental observables is one of the most important challenges in our field. Recent studies show that the Pearson Correlation Coefficient (PCC) between $v_n$ and event-wise mean transverse momentum $[p_\mathrm{T}]$, $\rho_n(v_n, [p_\mathrm{T}])$, and $[p_\mathrm{T}]$ fluctuations can probe several ingredients of the initial state. This talk presents precision measurements of $v_n-[p_\mathrm{T}]$ correlation for n=2,3 and 4 and high order $[p_\mathrm{T}]$ fluctuations in $^{129}$Xe+$^{129}$Xe and $^{208}$Pb+$^{208}$Pb collisions, and they are found to be small in the mid-central and central collisions in these systems. The $\rho_n$ and variance and skewness of $[p_\mathrm{T}]$ fluctuations show non-monotonic dependence on centrality, $p_\mathrm{T}$ and $\eta$. It was also found that the result depends on the centrality estimator used in the analysis, indicating a strong influence of volume fluctuations. In central collisions, where models generally show good agreement, the $v_2$--$[p_\mathrm{T}]$ correlations are sensitive to the triaxiality of the quadrupole deformation. A comparison of the model with the Pb+Pb and Xe+Xe data confirms that the $^{129}$Xe nucleus is a highly deformed triaxial ellipsoid that has neither a prolate nor oblate shape. This provides strong evidence for a triaxial deformation of the $^{129}$Xe nucleus from high-energy heavy-ion collisions.

Sprecher: Dr. Ivan Gnesi (CERN, Geneva (Switzerland), INFN LNF Frascati (Italy), CREF Rome (Italy), UniTo Turin (Italy))

Gnesi_HP2023_poster129_v2.pdf

18:15 Identifying quenched jets with machine learning

Measurements of jet substructure in ultra-relativistic heavy ion collisions suggest that the jet showering process is modified by the interaction with quark gluon plasma. Modifications of the hard substructure of jets can be explored with modern data-driven techniques. In this study, a machine learning approach to the identification of quenched jets is designed. Jet showering processes are simulated with a jet quenching model Jewel and a non-quenching model Pythia 8. Sequential substructure variables are extracted from the jet clustering history following an angular-ordered sequence and are used in the training of a neural network built on top of a long short-term memory network. We show that this approach successfully identifies the quenching effect in the presence of the large uncorrelated background of soft particles created in heavy ion collisions.

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based on arXiv: 2206.01628

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Sprecher: Julia Velkovska (Vanderbilt University), Yilun Wu (Vanderbilt), Yilun Wu (Vanderbilt University)

HardProbePoster_Mar17.pdf

18:15 Jet Quenching with JEWEL+vUSPhydro+$\rm T_RENTo$

We have studied the influence of realistic modeling of the medium formed in
Relativistic Heavy-Ion collisions on Jet Quenching phenomena. We used JEWEL to
simulate the medium modified parton shower and coupled it with vUSP-hydro$+\rm T_RENTo$ models. We have studied the influence of these combination of models on jet observables
such as $R_{AA}$, jet mass, $x_J$ and subjet fragmentation. We have
benchmarked our method with some of these observables and observed significant
differences in these observables behavior when a realistic hydrodynamics is used on them.

Sprecher: Fabio de Moraes Canedo (University of São Paulo (USP))

18:15 JEWEL and jet substructure in any collision system

Understanding the apparent absence of the modification of high-$p_T$ partons in small colliding systems has become critical. A major avenue of investigation that remains largely unexplored is the identification of observables that are experimentally more robust in small colliding systems than the traditional $R_{AA}$. In recent years the study of jet substructure observables in heavy-ion collisions has accelerated and we now have at our disposal several promising observables that merit investigation in small systems. In order to facilitate the process of comparing analytically viable observables with existing and future experimental results, we have developed a plugin for JEWEL (Jet Evolution With Energy Loss) that allows the user to pass hydrodynamic profiles from any collision system to JEWEL. Code suitable for use with (2+1)D temperature and fluid velocity profiles, fully compatible with the newest available version of JEWEL will be made available publicly, as well as simple RIVET analyses. We briefly detail the particularly careful treatment of the local fluid velocity, and present several jet substructure observables in a variety of collision systems.

Sprecher: Isobel Kolbé (IGFAE)

18:15 Longitudinal momentum fraction of heavy flavor meson in jets in high-energy nuclear collisions

Heavy flavor jets are powerful tools to gain insight into the in-medium partonic energy loss mechanisms and the transport properties of the quark-gluon plasma (QGP) in high-energy nuclear collisions. In this work, we present the first theoretical study of the longitudinal momentum fraction $z_{||}$ carried by $\rm{D^0}$ meson in jets in Pb+Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. The p+p baseline is provided by POWHEG+PYTHIA8 which matches the next-to-leading order hard processes with the parton shower. The in-medium evolution of heavy quark jets is employed by a Monte Carlo transport model which takes into account the collsional and radiative partonic energy loss in the expanding QGP. We observe steeper $z_{||}$ distributions of $\rm{B^0}$-jet compared to that of $\rm{D^0}$-jet at the same kinematics region in p+p collisions, which may be a hint of the harder jet fragmentation function of b-jet compared to c-jet in vacuum. In A+A collisions, it is shown that the jet quenching effect would in general decrease the values of $z_{||}$. In addition, we predict visibly stronger nuclear modifications of $\rm{B^0}$-jet $z_{||}$ distributions compared to $\rm{D^0}$-jet within the same $p_{\rm T}$ windows, as a result of the much steeper initial $z_{||}$ distribution of $\rm{B^0}$-jet in vacuum.

Sprecher: Wei Dai (China university of Geosciences)

18:15 Measurement of $\omega$ meson production in pp and p--Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02~$TeV with ALICE

The ALICE experiment at the LHC investigates the properties of the hot and dense nuclear matter created in heavy-ion collisions. By comparing the particle production in pp and p--Pb collisions, possible nuclear initial state effects can be isolated. Measurements of the $\omega$ meson $p_\text{T}$-spectra in pp and p--Pb collisions not only allow for a determination of the nuclear modification factor $R_\text{pA}$, but also provide insights into the fragmentation process and serve as vital input for direct photon cocktail simulations.

The $\omega$ mesons can be reconstructed in ALICE via their primary decay channel into three pions ($\omega\rightarrow\pi^+\pi^-\pi^0$). While the two charged pions are being directly identified by the tracking detectors, i.e. the Time Projection Chamber and the Inner Tracking System, the $\pi^0$ is reconstructed from its two decay photons. These photons can either be detected in the calorimeters or via tracks in case they convert to an electron-positron pair in the detector material.

In this poster, the measurement of the $\omega$ meson production in pp and p--Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02~$TeV will be presented. This includes the signal extraction and various corrections of the $\omega$ meson yields, as well as comparisons to theory calculations.

Sprecher: Nicolas Strangmann (Goethe University Frankfurt)

2023-03-24-Poster_5TeVOmega_HP.pdf

18:15 Measurement of $\omega$ mesons in pp collisions in $\sqrt{s}=13\,$TeV at the LHC with ALICE

Measurements of neutral mesons in small collision systems can serve as a baseline to understand modifications in heavy-ion collisions, where a QGP is formed.
These measurements can also be used to test pQCD predictions and to constrain fragmentation functions as well as parton distribution functions.
Furthermore, a precise knowledge of the $\omega$-meson production improves the measurement of direct photons, as photons produced in $\omega$ meson decays represent the third largest contribution of decay photon background.

This poster presents the invariant cross section of the $\omega$-meson in pp collisions at a center-of-mass energy of $\sqrt{s}=13\,$TeV measured by ALICE via its dominant decay channel $\omega \rightarrow \pi^+ \pi^- \pi^0$.
While charged pions can directly be measured by the ALICE central barrel tracking detectors, neutral pions are reconstructed using their decay channel into two photons.
This reconstruction is realized with several complementary methods using the ALICE calorimeters as well as the central barrel tracking detectors.
The combined result covers an unprecedented $p_T$ range with competitive statistical and systematic uncertainties.

Sprecher: Jens Robert Lühder

2023-03-15-HardProbes2023_Poster.pdf

18:15 Measurement of $\Xi_{c}^{0}$ via the semileptonic decay channel in $pp$ collisions and in $p$–Pb collisions with ALICE

Recent results of charmed baryon production in $pp$ collisions showed a significant enhancement of the baryon-to-meson ratio compared with the expectation based on $e^{+}e^{-}$ collisions. This indicates that the charm fragmentation into hadrons is not an universal process among different collision systems, and different mechanisms may play a role in the hadronic collisions with respect to $e^{+}e^{-}$ collisions. Therefore, the measurements of charmed baryon production are crucial to investigate the hadronisation mechanism of charm quarks. The production yield measurement of the $\Xi_{c}^{0}$ baryon has been measured in $pp$ collisions at $\sqrt{s}=$ 5 and 13 TeV. Further studies of the multiplicity dependence of the baryon-to-meson yield ratios can provide more information on how the charm hadronisation processes evolve from small to large collision systems. Measurements in $p$-Pb collisions are important to separate the cold nuclear matter effects from the effects associated with the formation of quark-gluon plasma. In this contribution, the most recent measurements of the $\Xi_{c}^{0}$ production via the semileptonic decay channel $\Xi_{c}^{0}\to \Xi^{-}e^{+}\nu_{e}$ in $pp$ collisions and the analysis status for the study of multiplicity dependence in $pp$ and $p$-Pb collisions will be shown.

Sprecher: Sanghoon Lim (Pusan National University)

Xic0_HP23_v3.pdf

18:15 Measurement of jet performance in proton-lead collisions in the ATLAS experiment

Jets can be copiously produced in heavy-ion collisions at the LHC energies. Their calibration is crucial for precise measurements of various processes, such as top-quark pair production. The poster presents the measurement of jet energy scale and resolution in proton-lead collisions collected at 8.16 TeV in 2016. The balance between Z boson and jet transverse momenta is explored for jet $p_\mathrm{T}> 20\;\mathrm{GeV}$ and $|\eta|<2.5$ to estimate jet performance in both data and simulation. The performance of two jet definitions, referred to as EMPFlow and HIJets, is studied and results are compared including systematic uncertainties. The presented results are a key input to the ongoing analysis of top-quark pair production in p+Pb collisions.

Sprecher: Patrycja Potępa (AGH University of Science and Technology / Johannes Gutenberg Universitaet Mainz)

HP2023-Potępa.pdf

18:15 Measurement of neutral meson production as a function of multiplicity in pp collisions at $\sqrt{s}$ = 13 TeV with ALICE

The precise measurement of the neutral meson production in pp collisions can be used to constrain fragmentation functions and parton density functions needed by pQCD calculations. Additionally, those measurements serve as input for direct photon analyses.
Moreover, the dependence of the neutral meson cross section on the event charged-particle multiplicity could give further insight into possible final-state effects in high-multiplicity pp collisions, in which other measurements show surprising similarities with those in heavy-ion collisions.

The analysis combines results from several partially independent reconstruction techniques available in ALICE. The decay photons were either detected with the electromagnetic calorimeters, or via the central tracking system using $\rm{e}^+\rm{e}^-$ pairs from conversions in the detector material.
The combination of these methods allows for a large $p_{\rm T}$ coverage, as well as small statistical and systematic uncertainties.

In this poster, the invariant cross sections of the $\pi^0$ and $\eta$ meson in pp collisions at $\sqrt{s}$ = 13 TeV, measured with ALICE, for different charged-particle multiplicity classes will be presented. The measurement covers 0.2 $\leq$ $p_{\rm T} <$ 200 GeV/$c$ for the $\pi^0$ and 0.4 $\leq$ $p_{\rm T} <$ 50 GeV/$c$ for the $\eta$ meson. Furthermore, the results will be compared to predictions from event generators and pQCD calculations.

Sprecher: Joshua Koenig (Goethe-Universität Frankfurt)

2023-03-21-poster_HP_V3_2023.pdf

18:15 Measurement of non-prompt $\rm D^0$ production in p-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV with ALICE

Measurements of the production of hadrons containing heavy quarks (charm and beauty) allow a study of cold nuclear matter (CNM) effects such as gluon saturation, shadowing and energy loss in p-Pb collisions. Understanding these effects is important for the proper interpretation of results in Pb-Pb collisions. In addition, the measurements provide the possibility to investigate the hadronisation mechanism.

In this poster, the first measurement of production cross section and nuclear modification factor of the $\rm D^0$ originating from beauty hadron decays, called non-prompt $\rm D^0$, at midrapidity in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV with the ALICE detector will be presented. The non-prompt baryon-to-meson yield ratio $\Lambda_{\rm c}^{+}/\rm D^{0}$ will be discussed as well.

Sprecher: Mingyu Zhang (Central China Normal University)

18:15 Measurement of the event multiplicity dependence of J/psi production in p+p collisions at √s = 500 GeV with STAR at RHIC

We present a new high-statistics measurement of inclusive $J/\psi$ production versus event multiplicity in $p$+$p$ collisions at $\sqrt{s} = 500$ GeV with the STAR experiment at RHIC. At mid-rapidity, calorimeter-triggered events are selected for candidate $J/\psi$ detection in the dielectron decay channel. Existing measurements at both $\sqrt{s} = 200$ GeV from STAR and $\sqrt{s} = 7$ TeV from ALICE have shown a faster-than-linear rise as a function of mid-rapidity multiplicity. Potential dependence on collision energy is examined, and measurements are made separately for several intervals over a broad $J/\psi$ transverse momentum range. Proposed explanatory mechanisms, including multi-parton interactions, string screening, and high gluon radiation are discussed, along with the guidance this measurement and related probes provide to model calculations.

Sprecher: Brennan Schaefer (Lehigh University)

18:15 Measurement of the transverse momentum($j_\mathrm{T}$) distributions of charged-particle jet fragments in pp collisions at $\sqrt{s}$ = 5.02 TeV with ALICE

Jet fragmentation allows us to explore the evolution process of the QCD jets. It can be studied using the transverse momentum ($j_\mathrm{T}$) and longitudinal momentum fraction ($z$) of constituent particles. The $j_\mathrm{T}$ distributions of jet fragments have been measured in pp and p—Pb collisions at $\sqrt{s}$, $\sqrt{s_{NN}}$ = 5.02 TeV with ALICE, and various parton-shower models reasonably describe the pp results. In this analysis, we extend the analysis to more detailed measurements of $j_\mathrm{T}$ distributions for charged-particle jets in pp collisions, in several $z$ ranges. The $z$-dependent $j\mathrm{T}$ distributions will be compared with the theoretical predictions to test our current understanding of jet fragmentation and hadronisation.

Sprecher: Jaehyeok Ryu (Pusan National University)

HardprobePoster_JetJt_JRyu.pdf

18:15 Modification of $b$ quark hadronization in high-multiplicity $pp$ collisions at LHCb

The differences in hadron chemistry observed at $e^{+}e^{-}$ machines versus hadron colliders may indicate that the mechanisms by which partons evolve into visible matter are not universal. In particular, the influence of the underlying event in hadron collisions requires further study. With full particle ID, precision vertexing, and a high rate DAQ, the LHCb detector is uniquely well suited to study the hadronization of heavy $b$ quarks. This talk will present LHCb data on hadronization of heavy bottom quarks, and discuss the status of a new LHCb analysis of bottom baryon production versus charged particle multiplicity.

Sprecher: julie napora (Los Alamos National Laboratory)

18:15 Multiplicity dependence of charged-particle jet properties in pp and p-Pb collisions with ALICE

Measurements of jet properties in small systems provide insights into perturbative and non-perturbative QCD aspects of jet structure and cold nuclear matter effects. Additionally, recent studies of high-multiplicity final states in small collision systems exhibit signatures of collective effects that are conventionally associated with the formation of hot and dense, color-deconfined QCD matter. However, no evidence of jet quenching has been observed within present accuracy in small collision systems. In this talk we will present recent ALICE measurements of intra-jet properties in pp collisions at $\sqrt{s}= 13$ TeV and p-Pb collisions at $\sqrt{s}= 5.02$ TeV: mean charged-constituent multiplicity, transverse momentum profile, and fragmentation distributions. These jet properties are compared between high-multiplicity and minimum-bias events in small collision systems. In addition, we will compare these results with various Monte Carlo generators.

Sprecher: Frau DEBJANI BANERJEE (Bose Institute), Reynier Cruz-Torres

18:15 Nuclear modification of charged hadrons and jets in isobar collisions at $\sqrt{s_{NN}}$ =200 GeV at STAR

Partonic scatterings with high momentum transfer occur before the formation of the quark-gluon plasma (QGP) in heavy-ion (A+A) collisions and result in collimated collections of hadrons called jets. The modification of the parton shower in the QGP compared to that in proton-proton (p+p) collisions offers insight into the nature of the medium's interaction with colored probes. Typically, this is measured as a ratio of hadron or jet spectra in A+A and p+p collisions called the $R_{\rm{AA}}$. The nominal RHIC A+A collision species is gold (Au) with 197 nucleons, but the high-statistics 2018 STAR isobar data from Zr+Zr and Ru+Ru collisions, each with 96 nucleons, offer the opportunity to study the system size dependence of nuclear modification of hard probes.

In this talk, we present a measurement of the inclusive charged hadron $R_{\rm{AA}}$ differentially with average number of participants (<$N_{\rm{part}}$>) in isobar collisions at STAR. The large available range of <$N_{\rm{part}}$> in these data allows for comparisons to small systems and Au+Au results. We also present ongoing work to control the path length of the partons through the medium via event shape engineering. Events are categorized by their eccentricity, and within a given eccentricity and centrality class, jets traveling in the event plane direction are compared to those traveling perpendicular to it, in order to study the dependence of jet energy loss on the collision geometry.

Sprecher: Isaac Mooney (Yale University)

FINAL_Mooney_HP23Poster.pdf

18:15 Nuclear PDF determination using Markov Chain Monte Carlo methods

Nuclear parton distribution functions (nPDFs) are an essential part in predictions of heavy-ion collisions. nPDFs have been determined via "global QCD analysis" in which nPDF-dependent prediction of a given process compares with its actual measurement. The challenging part of nPDF extraction is the uncertainty estimation. The most common approach for this purpose is Hessian method which has certain shortcomings, especially in the case of nuclear PDFs. In this presentation I will show a case study for an alternative approach where nPDF uncertainties are estimated using the Markov Chain Monte Carlo (MCMC) methods.

Sprecher: Nasim Derakhshanian (Institute of nuclear physics PAN)

Poster_hardprob.pdf

18:15 Open heavy flavour production from the high mass dilepton spectrum in pp collisions at $\sqrt{s}$ = 13 TeV with ALICE

Production measurements of heavy quark pairs in pp collisions are a known tool to test perturbative quantum chromodynamics calculations. In addition, they provide a reference for the corresponding studies in nuclear collisions. Indeed, in Pb-Pb collisions, the heavy quarks are produced at the early stages of the collision and can then experience full medium evolution. Open heavy flavor hadrons can therefore probe the quark-gluon plasma properties, as they are sensitive to the heavy quark energy loss in medium. A detection technique that was little explored at LHC energies is the analysis of the high-mass (i.e above the J/$\psi$ mass) continuum of the dilepton invariant mass spectrum, which is dominantly populated by semi-leptonic decays of charm and beauty hadron pairs in pp collisions.
In this presentation, new preliminary results from ALICE on the extraction of the charm and beauty hadron contributions to the high-mass dimuon continuum, at forward rapidity in pp collisions at $\sqrt{s}$ = 13 TeV, will be presented. Results from Pythia 8 Monte Carlo simulations used as input for the template fit of the data will be discussed.

Sprecher: Michele Pennisi (INFN Torino)

MPennisi_HP_poster_v3.pdf

18:15 Particle yield modification in jet-like azimuthal V$^0$ -hadron correlations in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV with ALICE

Two-particle azimuthal correlations are a powerful tool to investigate the details of the mechanisms of jet quenching and hadron production. Suitable candidates for these studies are strange mesons ($\mathrm{K^{0}_{S}}$) and baryons ($\Lambda/\overline{\Lambda}$), as their relative production rates differ for jets originating from quark or gluon. Measurements of near- and away-side hadron yields associated with these hadrons as trigger particles therefore provide additional constraining power for in-medium energy loss of different high-$p_{\rm T}$ partons and their fragmentation properties.

In this contribution, we present ratios of per-trigger yields in Pb-Pb collisions with respect to pp collisions, $I_{\mathrm{AA}}$ measured at midrapidity in the most central 0-10% collisions with the ALICE detector, with $\mathrm{K^{0}_{S}}$, $\Lambda/\overline{\Lambda}$ and charged hadrons as trigger particles. A significant enhancement of $I_{\mathrm{AA}}$ for various particle species is found at the lowest associated-particle $p_\mathrm{T,assoc}$ on both the near- and away-side, while a strong suppression of $I_{\mathrm{AA}}$ for $p_\mathrm{T,assoc}$ $>3$ $\mathrm{GeV}/c$ on away-side is observed, as expected from strong in-medium energy loss. The data are compared to HIJING, AMPT and EPOS models, where the latter two qualitatively describe the near- and away-side yield modifications at intermediate and high $p_\mathrm{T,assoc}$.

Sprecher: Herr Mustafa Anaam

Particle yield modification poster_cc.pdf

18:15 Prompt photon production with up to three jets in POWHEG

The production of prompt photons in association with jets is a very sensitive probe of the gluon distribution in light and heavy nuclei as well as of the properties of the quark-gluon plasma. We present a new calculation of prompt photon production with up to three jets at next-to-leading order of (NLO) QCD matched to parton showers with the POWHEG method. As applications, we examine correlations between the photon and the produced up to three jets as well as different approaches to photon fragmentation.

Sprecher: Alexander Puck Neuwirth

hp-2023.pdf

18:15 Quarkonium in the QGP from $N_f=2+1$ lattice QCD

We present unquenched correlator data and corresponding reconstructed spectral functions for quarkonium in both pseudoscalar and vector channels. Correlators are obtained using clover-improved Wilson fermions on $N_f=2+1$ HISQ lattices. To be on the constant line of physics bare quark masses are tuned to reproduce the mass spectrum of quarkonium by comparing the mass spectrum obtained from the lattice QCD with experimental values from the particle data group. For the spectral reconstruction, we use models based on perturbative spectral functions from different frequency regions like resummed thermal contributions around the threshold from pNRQCD and vacuum contributions well above the threshold. We show preliminary results of the reconstructed spectral function obtained for the first time in our study for full QCD. In addition, we compare the results with the previous continuum extrapolated results in the quenched approximation.

Sprecher: Sajid Ali (Bielefeld University, Germany)

2023_HardProbes_Poster_Sajid_Ali.pdf

18:15 Quarkonium production and flow in small systems measured with ALICE

Quarkonium measurements in hadronic collisions can provide insights into quantum chromodynamics (QCD). The quarkonium formation involves both the perturbative and non-perturbative regimes of QCD and the mechanisms at play are not yet fully understood. In order to get new insights and help constraining model calculations, ALICE has measured several quarkonium observables in proton-proton (pp) collisions at $\sqrt{s}$ = 13 TeV. At this energy, new preliminary $\Upsilon$ cross section measurements, as well as the results of the J/$\psi$ elliptic flow $v_{2}$ and double J/$\psi$ production, will be presented. In addition, the contributions of prompt and non-prompt J/$\psi$ can also be measured with ALICE detector.
In this contribution, we present new published results on the prompt and non-prompt J/$\psi$ production at midrapidity in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 8.16 TeV. Finally, a first look at the quarkonium mass spectrum, produced at both mid and forward rapidity using fresh Run 3 data collected in pp collisions at $\sqrt{s}$ = 13.6 TeV will be shown.

Sprecher: Tabea Maria Eder

HP_quarkonium_poster_final.pdf

18:15 Shear and bulk viscous coefficients in thermal QCD within the weak magnetic field regime

We have studied the shear ($\eta$) and bulk ($\zeta$) viscosities of hot QCD medium in a weak magnetic field. These viscosities are calculated by using the relaxation time approximation of kinetic theory in weak magnetic field limit, where temperature scale dominates over the energy scale related to magnetic field. It is found that the weak magnetic field reduces both $\eta$ and $\zeta$, contrary to their enhancement at finite chemical potential. So, the magnetic field decreases the momentum transfer across and along the layer, whereas the density facilitates this. This study sheds light on the sound attenuation through the Prandtl number (Pr), the nature of flow through the Reynolds number (Re), the fluid characteristic and the conformal symmetry of medium through the ratios $\eta/s$ and $\zeta/s$, respectively. Weak magnetic field increases the Prandtl number, whereas finite chemical potential reduces it. The observation on the Prandtl number also indicates that the energy dissipation due to the sound attenuation is mostly carried out by the momentum diffusion. The Reynolds number gets increased in a weak magnetic field and gets decreased at finite chemical potential, thus explaining that the weak magnetic field makes the medium less viscous, whereas the chemical potential makes the viscous nature of medium more evident. It is observed that, in a magnetic field, $\eta/s$ gets closer to the lower bound $1/(4\pi)$ and $\zeta/s$ gets nearer to the value at conformal symmetry.

Sprecher: Dr. Shubhalaxmi Rath (Indian Institute of Technology Bombay)

18:15 Stabilizing complex Langevin for real-time gauge theory

Direct computations of QCD real-time observables like transport coefficients are very difficult due to the infamous sign problem. The complex Langevin (CL) method is a promising approach to overcome it by using a real-time formulation of QCD on a complex time contour. Studying SU($N_c$) gauge theories with CL, we find that current stabilization techniques are insufficient to obtain correct results. Therefore, we introduce a novel anisotropic kernel that enables CL simulations on discretized time contours. Applying it to SU(2) pure gauge theory in 3+1 dimensions, we obtain unprecedentedly stable results that may allow us to calculate real-time observables from first principles in the near future.

Sprecher: Kirill Boguslavski (TU Wien)

HardProbes2023_Poster.pdf

18:15 Studies of large-$R$ jets and their substructure in Pb+Pb and $pp$ collisions with ATLAS

Measurements of the jet substructure in Pb+Pb collisions provide information on the jet quenching in the quark-gluon plasma (QGP) created in these collisions, over a wide range of energy scales. This poster presents ATLAS measurement of the suppression of yields of large-radius jets and its dependence on the jet substructure, characterized by the presence of sub-jets. This measurement is performed using the large Pb+Pb data sample at the center-of-mass energy of 5.02 TeV recorded in 2018 and compared to the result from $pp$ collisions at the same collision energy. Studies of the suppression of inclusive yields of large-$R$ jets probe the angular redistribution of energy in the parton shower and medium response when compared to existing measurements of suppression of smaller jets. Further, this measurement might provide new information about the scales at which jet constituents lose energy coherently or as independent color charges.

Sprecher: Martin Spousta (Charles University)

18:15 Study of multiplicity-dependent charmonia production in $p$+$p$ collisions at PHENIX

The production of quarkonia in high-energy heavy-ion collisions has been studied extensively to understand their production mechanisms and properties of Quark-Gluon Plasma (QGP). PHENIX has the capability to measure $J/\psi$ with muon arms at forward and backward rapidity ($1.2<|y|<2.2$) and charged particle multiplicity with silicon trackers at various acceptance ranges. The recent PHENIX study shows an increasing trend of $J/\psi$ yields versus multiplicity in $p$+$p$ collisions, which implies that the multi-parton interactions contribute to the $J/\psi$ production at the RHIC energy. $\psi(2S)$ have the same quark contents as $J/\psi$ but different binding energies, so $J/\psi$ and $\psi(2S)$ are expected to be modified differently due to the final-state effect like interaction with nuclear mediums or co-moving particles. Such different modifications can be applied to $A$+$A$ collisions, even in small systems like $p$+$A$ collisions; thus, understanding the modification mechanism is crucial for the precise understanding of the whole production mechanism. It will be very interesting to extend the study of the relative production of two states in various multiplicity ranges of $p$+$p$ collisions. In this talk, we will present the study of multiplicity-dependent production of charmonia in $p$+$p$ collisions with PHENIX, along with comparisons to the results from other experiments and MC based on PYTHIA8.

Sprecher: Sanghoon Lim (Pusan National University)

HP2023_poster_PHENIX_shlim.pdf

18:15 Substructures of heavy flavor jets in $pp$ and Pb+Pb collisions at $\sqrt{s}$ = 5.02~TeV

Groomed jet substructure measurements, the momentum splitting fraction $z_g$ and the groomed jet radius $R_g$, for inclusive, D$^0$-tagged and B$^0$-tagged jets in $pp$ and central Pb+Pb collisions at $\sqrt{s}=5.02$ TeV are investigated. Theoretical results for light-quark initiated and gluon initiated jets are provided as references though experimentally indistinguishable for now. Charged jets are constrained in a relative low transverse momentum interval 15 $\leq p_{\rm T}^{\rm jet\ ch} <$ 30 GeV/$c$ where the QCD emissions are sensitive to mass effects. The mass hierarchy manifests in $z_g$ distributions in both parton showering and jet quenching indicating steeper splitting functions of heavier partons. The flavour differences induced by Casimir factors do not contribute to $z_g$ distributions. Balanced splittings are suppressed due to jet quenching effects. The competition between flavor effects and mass effects to emission-angle distributions is directly observed for the first time. In both $pp$ and Pb+Pb collisions, the mass hierarchy in $R_g$ of inclusive, D$^0$-tagged and B$^0$-tagged jets is broken due to contributions from gluon-initiated jets. $R_g$ shift to more broaden distributions due to medium-induced modifications.

Sprecher: Qing Zhang (Central China Normal University), Wei Dai (China university of Geosciences)

18:15 Suppression of leading particles and flavor correlation modifications in heavy ion collisions

We study the suppression of leading two hadrons within jets and the modifications of their flavor correlations in heavy ion collisions. The di-hadron system is robust against the underlying event background therefore allows its precision measurements. Their suppression is sensitive to any partonic energy loss mechanism and can be used to cleanly test the onset of jet quenching in the evolution history. Also, their flavor correlation probes hadronization in the last stage of jet evolution. We will discuss di-hadron observables in the context of the upcoming RHIC measurements and present studies based on a variety of Monte Carlo simulations, which will lead to realistic measurement in the near future.

Sprecher: Roli Esha (Stony Brook University)

HP_poster.pdf

18:15 The jet physics program with sPHENIX

In Spring 2023, the sPHENIX detector at BNL’s Relativistic Heavy Ion Collider (RHIC) will begin measuring a suite of unique jet and heavy flavor observables with unprecedented statistics and kinematic reach at the RHIC energies.
The combination of electromagnetic calorimetry, hadronic calorimetry, precision tracking, and the ability to record data at a very high rates enables measurements of jets, jet substructure, and jet correlations at RHIC with a kinematic reach that will overlap with similar measurements at the LHC.  Jet observables are a particularly useful probe of the Quark Gluon Plasma (QGP) formed in heavy-ion collisions since the hard scatted partons that fragment into final state jets are strongly “quenched”, losing energy to the medium as they traverse it.   The detection method, physics projection and possible impacts to the field of heavy ion physics will be presented.

Sprecher: Megan Connors

HP_2023_sPHENIX_Jets_v4.pdf

18:15 The photon production and the collective flows from magnetic induced fusion and splitting in early stage of high energy nuclear collisions

In early stage of high energy nuclear collisions, the Lorentz contracted colliding nuclei nuclei fly near the light cone, with large-x partons acting as static sources of small-x modes that constitute the Color-Glass Condensate (CGC) fields. By interacting CGC fields, the chromoelectric and chromomagnetic fields are formed, they are the glasma fields. The glasma fields serve as initial condition for the evolution of classical gluon field at early stage which can be studied by Classical Yang-Mills equations. Noteworthily, in non-central collisions at early stage, the strong but short lived magnetic field is generated. Thus, interests of researchers have been triggered toward QCD matter with such extreme background.

As is known, photon is one of the most important probes in high energy nuclear collisions, and all its sources experience such intensive magnetic environment. In this talk, we are going to present our results of event-by-event study through 2+1D glasma simulations for mid-rapidity in overlap region of the two colliding nuclei. The photon can emit through gluon fusion or/and splitting in magnetic field. By including an IR regulator for the gluons, we'll show the non-trivial behavior of the photons' collective flows as well as the improvements ($v_2$ especially) on parton-hadronstring dynamics (PHSD) computations when comparing to the experiment measurements.

Sprecher: Moran Jia (Central China Normal University)

18:15 Thermalization and quark production in a spatially homogeneous system of gluons

We present a full set of the Boltzmann Equation in Diffusion Approximation (BEDA) for studying thermal equilibration of quarks and gluons. Using BEDA, we first analyse thermalization and quark production of spatially homogeneous systems initially made of pure gluons. We observe that soft partons, dominantly produced via medium-induced radiation, rapidly fill a thermal distribution with an effective (time-dependent) temperature and an effective Baryon chemical potential during the entire process. Without allowing quark production, the system is found to establish thermal equalibrium through distict three strages for initially under-populated cases and two stages for initially over-populated cases. Then, we study the production of quarks (and antiquarks) in such a system. The baryonic fermions are produced predominantly due to the $g \rightarrow qq$ splitting. We find that the quark production does not modify the early stages for both initially under- and over-populated systems due to Pauli blocking. During such early stages, the quark (and antiquark) number density increases linearly with time. In contrast, the later stages are modified significantly by quark production. The relation of our studies to those using effective kinetic theory and the jet evolution in QCD medium will also be discussed.

Sprecher: Sergio Barrera Cabodevila (Instituto Galego de Física de Altas Enerxías (IGFAE)), Bin Wu (IGFAE), Bin Wu (Universidade de Santiago de Compostela)

Hard_Probes_Poster-8.pdf

18:15 Topological separation of dielectron signals in Pb--Pb collisions with ALICE

Dielectrons are an exceptional tool to study the evolution of the medium created in heavy-ion collisions. In central collisions, the energy densities are sufficient to create a quark-gluon plasma (QGP). Thermal e$^{+}$e$^{-}$ pairs with invariant mass ($m_{ee}$) around 1.5 GeV/$c^{2}$ can be used to estimate the temperature of the QGP.
At LHC energies, the cross section of heavy-flavour (HF) production is large and correlated HF hadron decays dominate the dielectron yield for $m_{ee}>1.1$ GeV/$c^2$. Their contribution is modified in the medium compared to elementary collisions to an unknown extent, leading to large uncertainties in the subtraction of known hadronic sources. A topological separation based on the distance-of-closest approach ($DCA$) to the primary vertex is a promising alternative approach. The decay length of HF hadrons is of the order of $c\tau \approx 100-500\;\mu$m, hence their reconstructed decay electrons do not point to the primary vertex. This allows us to disentangle them from the prompt contribution of thermal dielectrons.
In this poster, preliminary results on the $DCA_{ee}$ spectra of dielectrons produced in Pb--Pb collisions at $\sqrt{s_{\text{NN}}}=5.02$ TeV with ALICE will be presented. The measurements are compared to reference distributions from simulations and expectations from theory. Finally, a first attempt to extract a prompt thermal contribution in the intermediate mass region is performed by fitting the measured $DCA_{ee}$ spectrum.

Sprecher: Jerome Jung (Goethe University)

18:30 Study of charm quark hadronization via $\Lambda_{\rm{c}}^{+}$ and $\rm{D}^{+}_{\rm{s}}$ production in the CMS experiment

Measurements of the lightest open-charm baryon, $\Lambda_{\rm{c}}^{+}$, production can provide important information about the quark coalescence process of hadronization in the quark-gluon plasma (QGP). With strange quark yields being enhanced in the presence of the QGP medium, the production of $\rm{D}^{+}_{\rm{s}}$ is expected to be enhanced in heavy ion collisions if recombination plays an important role in the hadronization process. The high-luminosity data sets collected by the CMS experiment in 2018 have been used to measure $\Lambda_{\rm{c}}^{+}$ production via $\Lambda_{\rm{c}}^{+} \to \rm{p}^{+} \rm{K}^{-} \pi^{+}$ in the $p_{\rm{T}}$ range 3--30 GeV /c for pp collisions and 6--40 GeV /c for PbPb collisions in different centrality classes. The $\rm{D}^{+}_{\rm{s}}$ production is measured via the decay channel $\rm{D}^{+}_{\rm{s}} \to \phi \pi^{+} \to \rm{K}^{+}\rm{K}^{-}\pi^{+}$ in the $p_{\rm{T}}$ range 2--40 GeV /c in pp collisions and 6--40 GeV /c in PbPb collisions using the data sets collected by CMS detector in 2015. Results of the differential cross section of $\Lambda_{\rm{c}}^{+}$ and $\rm{D}^{+}_{\rm{s}}$, the ratios of $\Lambda_{\rm{c}}^{+}$ and $\rm{D}^{+}_{\rm{s}}$ over $\rm{D}^{0}$ yields in pp and PbPb collisions will be presented along with the nuclear modification factors.

Sprecher: Soumik Chandra (PhD Student), Milan Stojanovic

Mittwoch, 29. März

09:00 → 10:20 Parallel: Early-Time Dynamics & nPDFs

Sitzungsleiter: François Arleo

09:00 J/$\psi$ photoproduction in Pb--Pb collisions with nuclear overlap at ALICE

Photonuclear reaction is induced by the strong electromagnetic field generated by ultrarelativistic heavy ion collisions. This process has been extensively studied in ultra-peripheral collisions (UPC). Photoproduced quarkonia are used to probe the nuclear gluon distributions at low Bjorken-$x$. In recent years, the coherent photoproduction of the J/$\psi$ vector meson has also been observed in A-A collisions with nuclear overlap. This observation raises several theoretical challenges, such as the survival of the coherence condition for a nucleus broken during the hadronic interaction or the possible interaction of the produced J/$\psi$ vector meson with a fast-expanding quark-gluon plasma medium. In this presentation, measurements of coherent J/$\psi$ photoproduction cross sections in Pb-Pb collisions for the 40-90$\%$ centrality range, measured by ALICE at midrapidity in the dielectron channel will be presented. In peripheral collisions, the $p_{\rm T}$-differential cross section is extracted for the first time at midrapidity. Final published results on coherent J/$\psi$ photoproduction cross sections at forward rapidity in the dimuon decay channel in the 10-90$\%$ centrality range will also be shown. Finally, the status of the new rapidity-differential measurement of coherently photoproduced J/$\psi$ at forward rapidity in the centrality range 70-90$\%$ will be discussed. Results will be compared with available theoretical models.

Sprecher: Ionut Cristian Arsene (University of Oslo)

IArsene_2023March29_v2.pdf

09:20 Far-from-equilibrium slow modes and momentum anisotropy in expanding plasma

We discuss the evolution of initial momentum anisotropy in the early-stage quark-gluon plasma. We use kinetic theory to study the far-from-equilibrium evolution of an expanding plasma with an anisotropic momentum-space distribution. We identify slow and fast degrees of freedom in the far-from-equilibrium plasma from the evolution of moments of this distribution. At late times, the slow modes correspond to hydrodynamic degrees of freedom and are naturally gapped from the fast modes by the inverse of the relaxation time.. At early times, however, there are an infinite number of slow modes. From the evolution of the slow modes we generalize the paradigm of the far-from-equilibrium attractor to vector and tensor components of the energy-momentum tensor, and even to higher moments of the distribution function that are not part of the hydrodynamic evolution. We predict that initial-state momentum anisotropy decays slowly in the far-from-equilibrium phase and may persist until the relaxation time.

Ref: Jasmine Brewer, Weiyao Ke, Li Yan, Yi Yin, ArXiv: 2212.00820

Sprecher: Yi Yin (Institute of Modern physics (CAS), China)

HP_shape_slow_pdf_v2.pdf

09:40 Investigation of initial state effects in p+Pb collisions at ATLAS via measurement of both top quark and dijet production

Proton-lead collisions at LHC energies offer unique possibilities to investigate the nuclear modifications of parton distribution functions (PDF) over a wide kinematic range. Several probes can be measured to characterize these effects in different kinematic regimes. The top-quark production is expected to be sensitive to effects at high Bjorken-x values, which are hard to access experimentally using other available probes. Conversely, dijet production can provide constraints on nPDFs over a wide kinematic range that extends down to Bjorken-x~$10^{-4}$. In 2016 the ATLAS experiment collected 164 nb$^{-1}$ of proton-lead collisions at a centre-of-mass energy of 8.16 TeV per nucleon pair. In this talk, we will present two new results obtained from the analysis of this dataset: the first measurement of the inclusive cross-section for top-quark pair production in dilepton and lepton+jets decay modes with electrons and muons, and the measurement of inclusive dijet cross-section. The results are compared to the NLO and NNLO predictions for dijet production and top-quark production using various PDF sets, respectively.

Sprecher: Riccardo Longo

Longo_HP2023_Final_v2.pdf

10:00 Anisotropic flow in small systems

Small systems display large anisotropic flow coefficients that can potentially be interpreted as a hydrodynamic signal. At these moderate multiplicities anisotropic flow is however relatively sensitive to subtle effects. These include the precise experimental procedure, rapidity coverage and gaps as well as effects due to resonance decays. In this talk we quantify these effects for pPb, OO and PbPb collision using the Trajectum framework including systematic uncertainties, so that a reliable hydrodynamic baseline can be attained.

Sprecher: Wilke van der Schee (CERN / Utrecht University)

talk_HP2023final.pptx

09:00 → 10:20 Parallel: Heavy Flavours & Quarkonia

Sitzungsleiter: Alessandro Grelli (Utrecht)

09:00 Heavy-flavour leptons and non-prompt D mesons to investigate beauty-quark interaction in the QGP with ALICE

In this contribution, new results for beauty measurements with ALICE are presented. The production of beauty hadrons can be accessed with measurements of leptons from beauty- and charm-hadron decays as well as the reconstruction of non-prompt charmed hadrons.
We show the nuclear modification factor of electrons from beauty hadron decays in Pb-Pb collisions at $\sqrt{s_{\rm \scriptscriptstyle NN}} = 5.02~{\rm TeV}$, which gives an insight into the production and momentum distribution of beauty quarks via the decays of the different hadron species. In order to understand the contributions from the different hadrons, we also present the final results for non-prompt ${\rm D}_{\rm s}^+$ mesons, which are compared to the prompt contribution as well as the non-prompt ${\rm D}^0$ measurement.
The azimuthal anisotropy of beauty quarks via the measurement of the non-prompt ${\rm D}^0$ $v_2$ is also discussed. It helps to further investigate the degree of themalization of beauty quarks in the hot and dense QCD medium. Additionally, ALICE can measure muons from heavy-flavour hadron decays in the forward direction $-4<\eta<-2.5$. The new results for the azimuthal anisotropy of heavy flavor muon production in p-Pb collisions at $\sqrt{s_{\rm \scriptscriptstyle NN}} = 8.16~{\rm TeV}$ provide new insights into the appearance of collective effects in smaller systems, which will be discussed and compared with measurements in Pb-Pb and pp as well as with model calculations.

Sprecher: Martin Völkl (Unversität Heidelberg)

VoelklHPnonPrompt.pdf

09:20 Constraining the in-medium heavy quark potential and diffusion coefficient within a unified perturbative and non-perturbative transport approach

While perturbative QCD is sufficient for understanding parton energy loss at large transverse momentum ($p_\mathrm{T}$) in heavy-ion collisions, a simultaneous description of the heavy flavor nuclear modification factor ($R_\mathrm{AA}$) and elliptic flow coefficient ($v_2$) at low to intermediate $p_\mathrm{T}$ still remains challenging due to non-perturbative interactions between heavy quarks and the QGP. We develop a unified perturbative and non-perturbative Boltzmann transport model for studying the heavy quark dynamics inside the QGP. A generalized Cornell-type potential is implemented, which incorporates both the short-range Yukawa interaction and the long-range color confining interaction. By combining this new approach to a (3+1)-dimensional viscous hydrodynamic model for the QGP evolution and a hybrid fragmentation-coalescence model for heavy quark hadronization, we obtain a satisfactory description of $R_\mathrm{AA}$ and $v_2$ of heavy mesons and their decayed leptons from low to intermediate to high $p_\mathrm{T}$. From the model-to-data comparison, we extract the in-medium heavy quark potential from open heavy flavor observables for the first time, which is shown in agreement with the lattice QCD calculation. The mass dependence of the heavy quark diffusion coefficient $D_s$ is systematically explored for the first time as well, which is shown to be smaller for $b$-quark than for $c$-quark, and is also consistent with recent results from the lattice calculation.

Sprecher: Wen-Jing Xing (Shandong University)

WJXing_HP2023_final.pdf

09:40 The heavy quark diffusion coefficient from 2+1 flavor lattice QCD

We present a novel approach to nonperturbatively estimate the heavy quark momentum diffusion coefficient, which is a key input for the theoretical description of heavy quarkonium production in heavy ion collisions, and is important for the understanding of the elliptic flow and nuclear suppression factor of heavy flavor hadrons. In the heavy quark limit, this coefficient is encoded in the spectral functions of color-electric and color-magnetic correlators that we calculate on the lattice to high precision by applying gradient flow. For the first time we apply the method to 2+1 flavor ensembles with temperatures between 200-350 MeV. Using our experience from quenched QCD, where we performed a detailed study of the lattice spacing and flow time dependence, we estimate the heavy quark diffusion coefficient using theoretically well-established model fits for the spectral reconstruction.

Sprecher: Olaf Kaczmarek (Bielefeld University)

HP2023_Kaczmarek.pdf

10:00 Measurement of $\mathrm{D_{s1}}^+$ and $\mathrm{D_{s2}}^{*+}$ production, and $\mathrm{D}^{*+}$ spin alignment in pp collisions at $\sqrt{s}=13$ TeV with ALICE

The understanding of the charm-quark hadronisation in high-energy hadronic collisions has recently improved. The production of D mesons relative to each other is compatible with those measured in $\mathrm{e^{+}e^{-}}$ collisions. The charm baryon-to-meson yield ratios show an enhancement from those measured at lepton colliders. This modification depends on the charged-particle multiplicity. State-of-the-art QCD-inspired models based on string fragmentation, statistical hadronisation, and hadronisation via recombination reproduce the main features of these measurements. However, several aspects of the transition of heavy quarks to the final-state hadron are not yet settled, such as the spin properties of produced particles. Hadronisation models can be further tested by the measurements of excited charm hadron states and of the polarisation or spin alignment of charm vector mesons. In this contribution, the first measurements of $\mathrm{D_{s1}}^{+}$ and $\mathrm{D_{s2}}^{*+}$ mesons and of $\mathrm{D}^{*+}$-meson spin alignment in pp collisions at $\sqrt{s}=13$ TeV by the ALICE Collaboration are presented. The measurement of the spin alignment is performed separately for prompt and non-prompt $\mathrm{D}^{*+}$ mesons, the latter are expected to be longitudinally polarised due to the helicity conservation. It is also shown how the latter coupled with the collective anisotropic expansion of the system may mimic the signal of global spin alignment in heavy-ion collisions.

Sprecher: Stefano Politano (Politecnico and INFN Torino (IT))

HP23_ALICE_DmesonReso_SPolitano_290323.pdf

09:00 → 10:20 Parallel: High-Momentum Hadrons & Correlations

Sitzungsleiter: Dr. Jasmine Brewer (CERN)

09:00 Energy Loss in Small Collision Systems

We consider some corrections relevant to energy loss in small collision systems, for which the temperature times the size of the system isn't large, $T\times L\sim1$.

First, we present the derivation of the explicit small path length correction to the DGLV opacity expansion. We then show first results from an energy loss model including these corrections, demonstrating the additional reduction in hadron suppression due to small collision systems (on top of the already reduced energy loss due to smaller pathlengths).

Second, we compute the NLO corrections to $\phi+\phi\rightarrow\phi+\phi$ scattering in $\phi^4$ theory on a spacetime with finite spatial extent. We show first results for the finite system size corrections to the running coupling, $\lambda(p,L)$: the finite system size reduces the magnitude of the coupling at small scales, $p\sim 1/L$. The origin of the corrections to the running coupling are generic; QCD, with its negative beta function, should thus see an increase in the momentum dependence of hadron suppression from small system corrections to the running coupling.

Deriving the above NLO corrections requires several novel techniques of broader theoretical interest. Most important, we present denominator regularization, a procedure that has all the advantages of dim reg but that has multiple advantages over dim reg, including working in spacetimes of fixed dimensionality and without any symmetries.

Sprecher: William Horowitz (University of Cape Town)

230329(HP).pdf

230329(HP).pptx

09:20 Enhancement of baryon-to-meson ratios around jets as a signature of medium response

We present a unique signal of jet-induced medium excitations: the enhancement of baryon-to-meson ratios around the quenched jets. To illustrate this, we study jet-particle correlations and the distributions of jet-induced identified particles with respect to the jet direction in Pb+Pb collisions at the LHC via a multi-phase transport model. We find a strong enhancement of baryon-to-meson ratios for associated particles at intermediate transverse momentum around the triggered jets in Pb+Pb collisions relative to p+p collisions, due to the coalescence of jet-excited medium partons. Since the lost energy from jets can diffuse to large angles, such baryon-to-meson-ratio enhancement is more pronounced for larger relative distance from the jet axis. We argue that the experimental confirmation of the enhancement of jet-induced baryon-to-meson ratios around the jets will provide an unambiguous evidence for the medium response to jet quenching in heavy-ion collisions.

[1] Ao Luo, Ya-Xian Mao, Guang-You Qin, En-Ke Wang, Han-Zhong Zhang, 2109.14314 [hep-ph]

Sprecher: Guang-You Qin (Central China Normal University)

Qin_BM_MR_v3.pdf

09:40 Pursuing the Precision Study for Color Glass Condensate in Forward Hadron Productions

With the tremendous accomplishments of RHIC and the LHC experiments and the advent of the future electron-ion collider on the horizon, the quest for compelling evidence of the color glass condensate (CGC) has become one of the most aspiring goals in the high energy quantum chromodynamics research. Pursuing this question requires developing the precision test of the CGC formalism. By systematically implementing the threshold resummation, we significantly improve the stability of the next-to-leading-order calculation in CGC for forward rapidity hadron productions in pp and pA collisions, especially in the high $p_T$ region, and obtain reliable descriptions of all existing data measured at RHIC and the LHC across all $p_T$ regions. Consequently, this technique can pave the way for the precision studies of the CGC next-to-leading-order predictions by confronting them with a large amount of precise data.

Sprecher: Yu Shi

SY_HP2023.pdf

10:00 Excited Hadron Channels in Hadronization

The proper treatment of hadronic resonances plays an important role for many aspects of heavy ion collisions. We expect this to be the case also for hadronization, due to the large degeneracies of excited states, and the abundant production of hadrons from their decays. We show how a comprehensive treatment of excited meson states can be incorporated into quark recombination, and in extension, into Hybrid Hadronization. We discuss in detail the quantum mechanics of forming excited states, utilizing the Wigner distribution functions of angular momentum eigenstates of isotropic 3-D harmonic oscillators. We describe how resonance decays can be handled, based on a set of minimal assumptions, by creating an extension of hadron decays in PYTHIA 8. Finally, we present a study of hadron production by jets using PYTHIA and Hybrid Hadronization with excited mesons up to orbital angular momentum L=4. We find that states up to L=2 are produced profusely by quark recombination.

Sprecher: Rainer Fries (Texas A&M University)

HP2023_Talks_RJFries.pdf

HP2023_Talks_RJFries.pptx

09:00 → 10:20 Parallel: Jets and their modification in QCD Matter

Sitzungsleiter: Dr. Edmond Iancu (IPhT, CEA-Saclay)

09:00 Exploring the QCD color charge dependence of jet quenching with photon+jet events in ATLAS

As high-energy light quarks and gluons traverse the Quark-Gluon Plasma, they are expected to lose energy mainly via medium-induced gluon bremsstrahlung. Thus, a basic assumption in pQCD-based frameworks of radiative energy loss is that it depends on the QCD color factor of the initiating parton. In this talk, ATLAS presents two measurements in Pb+Pb collisions aimed at constraining the magnitude of this color-charge dependence. First, ATLAS presents the finalized result on the nuclear modification factor RAA for photon-tagged jets. By comparing this measurement to the RAA for inclusive jets, one can exploit the known difference in the quark-/gluon-initiated jet fraction between these two samples and extract the QCD color-charge dependence. Second, ATLAS presents a new measurement of photon plus two jet production in Pb+Pb collisions. In these events, the two jets traverse the same QGP medium, but typically have different color charges (i.e. they are a quark and a gluon). Thus, measurements such as the total jet-to-photon $p_{\mathrm{T}}$ ratio, the two-jet $p_{\mathrm{T}}$ asymmetry, and the jet opening angle can provide interesting information on the parton-QGP interaction. Both results are compared to a variety of theoretical calculations.

Sprecher: Christopher McGinn (University Colorado Boulder, ATLAS and sPHENIX)

hardProbes2023_CMcGinn_20230329.pdf

09:20 Intra-jet asymmetry and jet-flow coupling in heavy-ion collisions

The interaction between the jet and QGP fluid will deflect particles associated with the jet from their initial direction. Such deflection will depend on the energy of the jet constitutes and the velocity of the flow. The soft particles suffering stronger deflection will drift towards the direction of the flowing medium, away from the center of the jet cone where the hard particles are located, leading to an angular intra-jet asymmetry of particle distribution coupled with flow inside the jet. The intra-jet asymmetry could be obtained by the angular distribution of jet constituents and the angle between the Winner-takes-all(WTA) and standard jet axis. In this work, we first calculate the contributions from jet particles with different pT to the jet shape to get the average effect of the jet-flow coupling. We further explore the intra-jet asymmetry of gamma-jet in both longitudinal and transverse directions and study their dependence on jet path length and fluid viscosity. Together with gamma-jet asymmetry, we can use the difference between the longitudinal and transverse intra-jet asymmetry to extract the velocity of the transverse flow and identify the initial production position of the jet. We also compare the differences between dijet and gamma-jet to investigate the effect of the diffusion wake. The rapidity ordering of particles with different pT shows an explicit picture of the jet-flow coupling effect in the longitudinal direction.

Sprecher: Tan Luo (IGFAE)

HP2023.pdf

09:40 Data-driven $\hat{q}$ in a hard-soft factorized parton energy loss approach

Interactions of high-energy partons with the strongly-coupled quark-gluon plasma lead to parton energy loss, as well as broadening of the partons' transverse and longitudinal momentum distributions. Energy loss and momentum broadening resulting from soft parton-plasma interactions can be quantified with transport coefficients, factorizing their effect from hard (perturbative) parton-plasma scatterings. We apply this factorized model of energy loss [1] to perform a Bayesian calibration against RHIC and LHC measurements, finding an enhancement of parton energy loss at low temperature compared to perturbative expectations. We highlight the model's ability to match perturbative calculations while inherently allowing for agnostic non-perturbative energy loss.

[1] T. Dai, J.-F. Paquet, D. Teaney and S.A. Bass, ``Parton energy loss in a hard-soft factorized approach,'' Phys.Rev.C 105 (2022) no.3, 034905

Sprecher: Steffen A. Bass (Duke University)

HP2023_Bass.pdf

10:00 Jet quenching in evolving anisotropic matter

Over the last decades, the theoretical picture of how hadronic jets interact with nuclear matter has been extended to account for the medium’s finite longitudinal length and expansion. However, only recently a first-principle approach has been developed that allows to couple the jet evolution to the medium flow and anisotropic structure in the dilute limit. In this talk, we will show how to extend this approach to the dense regime, where the resummation of multiple in-medium scatterings is necessary. Particularly, we will consider the modifications of the single particle momentum broadening distribution and single gluon production rate in evolving matter. The resummation is performed by either computing the opacity series or starting from the all order BDMPS-Z formalism. We will also discuss the (novel) resulting modifications to jets' substructure.

Sprecher: Andrey Sadofyev (IGFAE)

HP2023.pdf

HP2023.pptx

10:20 → 10:50 Coffee break

10:50 → 12:30 Parallel: Early-Time Dynamics & nPDFs

Sitzungsleiter: Gines MARTINEZ (Subatech (CNRS/IN2P3, IMT Atlantique, Nantes Universite))

10:50 Dilepton spectra as probes of the early stages of heavy-ion collisions

The early stages of heavy-ion collisions are largely unexplored experimentally, despite great theory progresses. In such collisions, electromagnetic radiation such as dileptons are produced throughout the history of the medium and probe its quark content. Hence, they are useful tools to investigate the early stages of the quark-gluon plasma, allowing to better understand its chemical and kinetic equilibration. The measurement of such observable is challenging; in particular, one important source of background is the Drell-Yan production of dileptons in the initial hard scatterings. In this contribution we present our estimate of the dilepton spectrum produced by the quark-gluon plasma starting from the early stages, in the intermediate mass range $1 < M < 5$ GeV/$c^2$, based on QCD kinetic theory. We also estimate the Drell-Yan background in this kinematic range using a state-of-the-art perturbative computation. Our calculation takes into account the anisotropy of the quark and gluon momentum distributions at early times, as well as the under-population of quarks relative to gluons. We investigate different characteristics of this spectrum, in particular its sensitivity to the equilibration time of the quark-gluon plasma, and its approximate scaling with transverse mass. Finally we investigate to what extent can the polarization of dilepton pairs provide a handle to separate the Drell Yan contribution from later dilepton production.

Sprecher: Maurice Coquet (Irfu/CEA)

HP2023_COQUET_v5.pdf

11:10 Probing a new regime of ultra-dense gluonic matter using high-energy photons with the CMS experiment

In ultraperipheral collisions (UPCs) of relativistic heavy ions, the coherent heavy-flavor vector meson production via photon-nuclear interactions is of particular interest, since its cross section is directly sensitive to the nuclear gluon density. However, in experimental measurements, because each of the two nuclei in symmetric UPCs can serve both as a photon-emitter projectile and a target, this two-way ambiguity has prevented us from disentangling contributions involving high- and low-energy photon-nucleus interactions, thus limiting our capability of probing the extremely small-$x$ regime, where nonlinear QCD effects are expected to emerge. In this talk, we will present a new measurement of coherent $\rm{J}/\psi$ photoproduction, where the two-way ambiguity is solved by implementing for the first time a forward neutron tagging technique in UPC PbPb collisions at 5.02 TeV. The coherent $\rm{J}/\psi$ photoproduction cross section will be presented as a function of the photon-Pb center-of-mass energy in UPCs up to about 400 GeV, corresponding to an extremely low $x$ of $\sim{5\times10^{-5}}$. We will discuss the physics implications of this new result, as well as exciting opportunities in future LHC heavy ion runs.

Sprecher: Wei Li (Rice University)

HP2023_UPCJPsi_WeiLi_v2.pdf

11:30 Universality of Energy-Momentum Response in Conformal Kinetic Theories

Viscous hydrodynamics serves as a successful mesoscopic description of the Quark-Gluon Plasma (QGP) on large time and distance scales. Since highly energetic Jets deposit part of their energy into the QGP in a very localized fashion, it is important to understand to what extent the propagation of the deposited energy can be described within hydrodynamics. We investigate this problem by studying the evolution of energy-momentum perturbations in kinetic theories, with varying gradients from microscopic to macroscopic scales. By comparing results for different microscopic theories (QCD, Yang-Mills, RTA, Scalars) we find a remarkable degree of universality, where the evolution of energy-momentum perturbations of the QGP is rather well described by one hydrodynamic mode and one non-hydrodynamic mode. We discuss the implications of our findings for the theoretical description of the medium response to Jets in Heavy-Ion collisions.

Sprecher: Xiaojian Du (Galician Institute of High-Energy Physics (IGFAE))

HP2023-XiaojianDu_3.pdf

11:50 Early time dynamics far from equilibrium via holography

We investigate the early time dynamics of heavy ion collisions studying the time evolution of the energy-momentum tensor as well as energy-momentum correlations within a uniformly thermalizing holographic QGP. From these quantities, we suggest a far-from equilibrium definition of shear viscosity, which is a crucial property of QCD matter as it significantly determines the generation of elliptic flow already at early times. During the the initial heating phase of the holographic QGP the shear viscosity of entropy density ratio decreases down to 60%, followed by an overshoot to 110% of the near-equilibrium value, $\eta/s=1/(4\pi)$. Subsequently, we consider a holographic QGP which is Bjorken-expanding. Its energy-momentum tensor components are analytically shown to have a hydrodynamic attractor to which all time evolutions collapse independent of the initial conditions. Based on this, we propose a definition for a far from equilibrium speed of sound that governs the propagation of sound modes in the holographic QGP. Implications for the QCD QGP are discussed.

Sprecher: Matthias Kaminski (University of Alabama)

Kaminski_EarlyTimeDynamics_HardProbes2023_MK29Mar2023.pdf

12:10 Enhancing the CERN LHC small systems program with bowling-pin-shaped neon isotopes

We demonstrate the unique opportunities for small systems studies offered by complementing the future run of $^{16}$O+$^{16}$O collisions at the CERN LHC with collisions of bowling-pin-shaped $^{20}$Ne isotopes.

1. Origin of collectivity: A comprehensive campaign of hydrodynamic calculations (~20 million simulated events) demonstrates that the impact of the extreme shape of neon on elliptic flow survives the large fluctuations due to the small nucleon numbers in the comparison O+O vs. Ne+Ne. Such modifications are robust against variations in hydrodynamic model parameters, and, if observed, will yield conclusive evidence of the geometric (and potentially hydrodynamic) origin of flow in systems presenting $dN/dy\approx100$.

2. Energy loss in small systems: Due to the extremely elongated $^{20}$Ne geometry, Ne+Ne collisions may help reveal hard-probe modification via path-length-dependent effects in the comparison with O+O collisions, without requiring a good centrality resolution. We estimate such effects based on the analysis of the path lengths expected to be traversed by the hard probes at realistic temperatures.

Based on Giacalone, Nijs, van der Schee, et al., arXiv:2212:XXXXX

Sprecher: Giuliano Giacalone (Universität Heidelberg)

GG_neon_.pdf

10:50 → 12:30 Parallel: Heavy Flavours & Quarkonia

Sitzungsleiter: Itzhak Tserruya (Weizmann Institute of Science)

10:50 Resolving the $R_{pA}$ and $v_2$ puzzle of $D^0$ mesons in $p-Pb$ collisions

It has been a challenge to understand the experimental data on both the nuclear modification factor and elliptic flow of $D^0$ mesons in $p−Pb$ collisions at LHC energies. In this $\rm{work^{[1]}}$, we study these observables with an improved multi-phase transport model. After including the Cronin effect (or transverse momentum broadening) and independent fragmentation for charm quarks, we provide the first simultaneous description of the $D^0$ meson $R_{pA}$ and $v_2$ data at $p_T$ ≤ 8 GeV/c. The model also provides a reasonable description of the $D^0$ meson $p_T$ spectra and the low-$p_T$ (below ~1.5 GeV/c) charged hadron spectra, $R_{pA}$ and $v_2$. We find that both parton scatterings and the Cronin effect are important for the $D^0$ meson $R_{pA}$, while parton scatterings are mostly responsible for the $D^0$ meson $v_2$. Therefore, it is crucial to include the Cronin effect for the simultaneous description of the $D^0$ meson $R_{pA}$ and $v_2$. Since the Cronin effect is expected to grow with the system size, this work also implies that it could be important for heavy hadrons in large systems.

Sprecher: Dr. Zi-Wei Lin

Ziwei-HP2023.pdf

11:10 Quarkonia dynamics in the Quark-Gluon Plasma with a quantum master equation

In recent years, a significant theoretical effort has been made towards a dynamical description of quarkonia inside the Quark-Gluon Plasma (QGP), using the open quantum systems formalism. In this framework, one can get a real-time description of a quantum system (here the quarkonium) in interaction with a thermal bath (the QGP) by integrating out the bath degrees of freedom and studying the system reduced density matrix.

We investigate the real-time dynamics of a correlated charm-anticharm pair inside the QGP using novel coupled quantum master equations derived from first QCD principles and based on the work of Blaizot & Escobedo [1]. The equations are solved numerically in 1D to lessen computing costs and are used to gain insight on the dynamics in both a static and evolving medium following a Björken-like temperature evolution. Several initial conditions will be explored and a study of a possible semi-classical treatment will be presented, in order to see if this approach
can be used to treat multiple charm-anticharm pairs at the same time.

[1]-J. P. Blaizot and M. A. Escobedo, Quantum and classical dynamics of heavy quarks in a quark-gluon plasma, J. High Energy Phys. 06 (2018) 034.

Sprecher: Stéphane Delorme (IFJ Pan)

TalkHP2023.pdf

11:30 Multiplicity dependence of quarkonium production in small systems with ALICE

High-multiplicity measurements in pp and p-Pb collisions have revealed the presence of phenomena typically attributed to the creation of a quark-gluon plasma (QGP). Events with multiple parton-parton interactions (MPIs) have been proposed as one possible explanation of this observation. MPIs play a significant role in describing the soft component of the hadronic interactions, and at LHC energies also affect the production of heavy quarks. Multiplicity dependent quarkonium measurements in small systems are therefore crucial for studying the correlation between soft and hard components of high-multiplicity events, as well as to shed light on MPIs or any other possible underlying mechanisms. Moreover, excited quarkonia, more loosely bound than ground states, are more sensitive to any possible dissociation mechanisms taking place in the final state.

In this contribution, new published multiplicity dependent $\psi$(2S) measurements, carried out at forward rapidity in pp and p-Pb collisions at $\sqrt{s}$ = 13 TeV and $\sqrt{s_{\rm NN}}$ = 8.16 TeV, along with charmonium excited-to-ground state ratios, will be discussed. Similar measurements published recently for $\Upsilon$($n$S) states ($n$ = 1,2,3), performed at forward rapidity in pp collisions at $\sqrt{s}$ = 13 TeV, will be presented. The status of ongoing multiplicity dependent J/$\psi$ measurements at midrapidity in pp and p-Pb collisions will also be shown. Results will be compared to available model calculations.

Sprecher: Ailec de la Caridad Bell Hechavarria

HardProbes_Ailec.pdf

11:50 Quarkonia and exotic hadron production in $p$Pb collisions at LHCb

Quarkonia production in hadronic collisions is an important experimental observable that sheds light on the heavy quark interaction with the nuclear medium. While the bound quarkonium states undergo dissociation and recombination in PbPb collisions, in $p$Pb collisions they can suffer from a combination of initial and final state effects such as shadowing and comover breakup. The exotic hadron X(3872), which likely contains a $c\bar{c}$ pair plus two light quarks, may be affected by similar phenomena plus modifications of the hadronization process that emerge in dense systems. This talk will discuss recent results on conventional charmonia from LHCb, and the first measurement of X(3872) production in $p$Pb collisions.

Sprecher: Clara Landesa Gómez (IGFAE)

HardProbes_LandesaGomezClara.pdf

12:10 Medium-enhanced $c\bar{c}$ production in jets

We show that the same QCD formalism that accounts for the suppression of high-$p_T$ hadron and jet spectra in heavy-ion collisions predicts medium-enhanced production of $c\bar{c}$ pairs in jets. Using the formalism of Baier-Dokshitzer-Mueller-Peigné-Schiff and Zakharov we compute the medium-modifications of the gluon splitting into a quark–anti-quark pair and reveal two phenomena: a medium-induced momentum broadening of quark–antiquark pairs, and a medium-enhanced production of such pairs. We perform a parton shower study to demonstrate that the medium-enhanced production of $ c\bar{c}$ pairs leads to enhanced production of jets containing $D^0 \bar{D}^0$. We estimate that this novel effect of jet-medium interaction could be measurable in high-luminosity heavy-ion runs at the LHC.

Sprecher: Jasmine Brewer (CERN)

JasmineBrewer-HP23.pdf

JasmineBrewer-HP23.pptx

10:50 → 12:30 Parallel: Jets and their modification in QCD Matter: I

Sitzungsleiter: Feng Li

10:50 ATLAS measurements of $b$-jet suppression and heavy-flavor azimuthal correlations in 5.02 TeV Pb+Pb collisions

The suppression of jets in heavy-ion collisions can provide detailed information about the hot, dense plasma formed in these collisions at the LHC. The energy loss mechanism can be studied by measuring differences in the suppression of $b$-tagged and inclusive jets in $pp$ and Pb+Pb collisions. Besides the $b$-tagged jet measurements, an alternative method for probing the interactions of heavy quarks with the plasma, is the study of the correlations between heavy-quark pairs, which is sensitive to the relative importance of collisional versus radiative scattering processes. We report new ATLAS measurements of $b$-tagged and inclusive jet production aND the measurement of the yield of correlated muon pairs from heavy-flavor decays in Pb+Pb and $pp$ collisions at $\sqrt{s_\textrm{NN}}~=~5.02$~TeV. For $b$-tagged and inclusive jet, the transverse momentum distributions in Pb+Pb and $pp$ collisions, as well as the nuclear modification factors, $R_{AA}$, in Pb+Pb collisions are presented togheter with comparisons to theoretical calculations. The measurement of correlated muon pairs from heavy-flavor decays includes per-event yields, scaled by the nuclear thickness function, $T_{AA} $, measured differentially as a function of centrality. Detailed studies of how the shape of the correlation in azimuthal-angle separation between the two muons, changes from peripheral to central Pb+Pb collisions, and comparison to the corresponding measurements in $pp$ collisions are also presented.

Sprecher: Sebastian Tapia (Universidad Tecnica Federico Santa Maria)

ATLAS_HF_HP23_v2.pdf

11:10 First measurement of jet angularities with D$^0$-meson tagged jets with ALICE

The properties of partonic fragmentation in QCD are dependent on the flavours of the partons involved in the 1$\rightarrow$2 splitting processes underpinning parton showers. These flavour dependencies arise due both to the different Casimir factors of quarks and gluons, as well as the mass of heavy quarks. Heavy-flavour jets provide a unique experimental tool to probe these flavour dependencies, particularly at low and intermediate transverse momenta where mass effects are significant. Here we report the first measurement of the angularity of jets tagged with a reconstructed D$^0$ meson, in the jet transverse momentum interval of 15-30 GeV/c. Generalised angularities are a set of IRC-safe jet-substructure observables which can be tuned in their sensitivity to the partonic fragmentation and hadronisation processes. Comparisons to angularity measurements in a flavour-untagged jet sample will probe both the flavour depdendences due of the mass of the charm quark, as well as the high purity quark nature of the D$^0$-tagged jet sample. Further comparisons to different MC generators will assess the role of these flavour dependencies in different parton shower prescriptions.

Sprecher: Preeti Dhankher (University of California Berkeley)

HFJet_Angularity_HP2023.pdf

11:30 Dead-cone searches in heavy-ion collisions using the jet tree

In this talk, we will discuss the possibility of using the dead cone of heavy quarks as a region of the Lund plane where medium-induced gluon radiation can be isolated and characterised. We propose to use jet grooming techniques to identify a particular splitting in the jet tree that is both perturbative and sensitive to the dead-cone effect. In particular, we introduce a new jet substructure groomer, dubbed Late-$k_t$, that selects the most collinear splitting in a QCD jet above a certain transverse momentum cutoff. Our observable is then defined as the angular distribution of the splitting tagged by Late-$k_t$. After discussing the logarithmic resummation structure of this new jet substructure observable, we demonstrate that medium-induced emissions lead to an enhancement of collinear emissions below the dead cone angle for b-initiated jets. Numerically, we demonstrate an excellent resilience of Late-$k_t$against uncorrelated thermal background, thus confirming this observable as a potential candidate to unveil medium dynamics around the dead cone regime.

Sprecher: Leticia Cunqueiro (Roma Sapienza)

HardProbes23_Cunqueiro.pdf

11:50 Exploring the deadcone effect in heavy ion collisions with energy correlators

The dynamics of jet formation in heavy ion collisions (HICs) is influenced by the presence of a quark-gluon plasma (QGP) and is imprinted into a jet's multi-scale substructure. In recent work, we demonstrated that the two-point energy correlator, measured on a massless in-medium jet, provides a sensitive probe of this dynamics and can robustly identify the scales defined by the properties of the QGP. In this talk we present the extension of our work to heavy flavour jets produced in HICs. This introduces new dynamics into the jet formation, namely the deadcone effect. We show that energy correlators allow us to disentangle the dynamics of the deadcone from interactions with the QGP. We identify two limits: the near-massless limit where the deadcone is not affected by the medium and measurements of medium properties follow similar profiles to the massless case, and the large-mass limit where the medium radiation begins to populate the deadcone producing a zombie cone. Building on our previous work, our study further demonstrates the spectacular ability of energy correlators to disentangle complicated competing jet dynamics.

Sprecher: Jack Holguin (CPHT, Ecole Polytechnique)

Deadcone29-03-2023.pdf

12:10 Exposing the dead-cone effect and constraining heavy quark splitting functions in heavy ion collisions

When an energetic parton traverses the hot QCD medium, it may suffer multiple scattering and energy losses. The medium-induced gluon radiation for a massive quark will be suppressed relative to that of a light quark due to the dead-cone effect. The development of new declustering techniques of jet evolution makes a direct study of the dead-cone effect in the QCD medium possible for the first time. In this work, we compute the emission angle distribution of the charm-quark initiated splittings in the D0 meson tagged jet and that of the light parton initiated splittings in inclusive jets in p+p and Pb+Pb at 5.02~TeV by utilizing the declustering techniques of jet evolution. When comparing the jet number normalized emission angle distributions of the charm-quark initiated splittings and that of the light parton initiated splittings by directly taking their ratios at the same energy intervals of the initial parton, one can find the charm-quark initiated splittings will be suppressed at smaller emission angle corresponding to the dead-cone effect. The dead-cone effect of the medium-induced gluon radiation can be directly observed. We further find that the dead-cone effect will broaden the emission angle of the splitting and reduce the possibility of such splitting occurring, leading to the massive parton losing less energy. Collisional energy loss will not obscure such observation. Also investigate the possible direct observable that help constrain heavy quark splitting function.

Sprecher: Wei Dai (China university of Geosciences)

WeiDAI_hardprobes.pdf

10:50 → 12:30 Parallel: Jets and their modification in QCD Matter: II

Sitzungsleiter: Dr. Jacopo Ghiglieri (SUBATECH, CNRS)

10:50 Quantum simulation of jet evolution in a medium

In recent years, a lot of effort has been put into expanding established jet-quenching formalisms to account for higher-order or energy-suppressed medium-induced effects. Understanding how such contributions emerge is important to have a more complete picture of jet evolution in the medium and to extract more detailed properties of the underlying matter. However, such efforts are in general plagued by technical difficulties related to the complexity of the calculations. In this talk, we will argue that quantum computers can be used as alternative theoretical labs to simulate jet evolution in the quark-gluon plasma. Based on the light-front Hamiltonian formalism, we construct a digital quantum circuit that tracks the evolution of a multi-particle jet probe within the $|q\rangle + |qg\rangle$ Fock sectors in the presence of a stochastic color background. Using the quantum simulation algorithm, we show that the jet evolution in the medium can be properly captured employing small lattices. Importantly, the simulations can be run in general stochastic backgrounds, surpassing many of the simplifying assumptions usually taken. We will show that the present strategy can be efficiently expanded to account for the production of multiple gluon radiations.

Sprecher: Wenyang Qian (University of Santiago de Compostela)

HP2023_v2.3.pdf

11:10 Pushing forward jet substructure measurements in heavy-ion collisions

In this talk, we introduce a novel approach to minimise selection biases associated to the modification of the quark- vs. gluon-initiated jet fraction in order to assess the presence of other medium-induced effects, namely color decoherence. More concretely, we propose to explore the rapidity dependence of jet substructure observables. So far, all jet substructure measurements at mid-rapidity have shown that heavy-ion jets are narrower than vacuum jets. First, we show analytically that if the narrowing effect persists at forward rapidities, where the quark-initiated jet fraction is greatly increased, this could serve as an unambiguous experimental observation of color decoherence dynamics in heavy-ion collisions. Next, we carry out Monte Carlo simulations using the expected statistics of the projected high-luminosity runs and demonstrate that this measurement is within reach of the future detector capabilities that will allow for an extended rapidity coverage both at LHC and RHIC, with STAR.

Based on: Pushing forward jet substructure measurements in heavy-ion collisions, D. Pablos, A. Soto-Ontoso. arXiv:2210.07901

Sprecher: Daniel Pablos (INFN Torino)

pablos_hp23.pdf

11:30 Measurement of Two-Point Energy Correlators Within Jets in p+p Collisions at $\sqrt{s}$ = 200 GeV

Jet substructure is a powerful tool to probe the time evolution of a parton shower. However, many of the analysis methods used to extract splitting formation times from jet substructure, such as Soft Drop grooming and the Lund plane, focus on the hardest radiation of the jet. A complementary observable with growing theoretical and experimental interest, the 2-point Energy Correlator (EEC), re-contextualizes jet substructure study by using the distribution of angular distance of all combinations of two final state particles within a jet. This distribution is weighted by the product of the fractions of jet energy that each of the constituents carry, and thus is infrared-and-collinear safe. The EEC can cleanly reveal the separation between two distinct regimes: effects originating from free hadrons at small opening angles and from perturbative fragmentation of quarks and gluons at large opening angles.

In this talk, the first fully corrected measurement of the EEC at RHIC is presented, using the data taken at $\sqrt{s}$ = 200 GeV $p+p$ collisions by STAR. The EEC will be shown for several full jet $p_T$ selections and compared to predictions from the PYTHIA-6 STAR tune. This work will be useful as a baseline for comparisons to future studies in heavy-ion systems, which will provide information about how the quark-gluon plasma interacts with the jet across different angular scales.

Sprecher: Andrew Tamis (Yale University)

Tamis_HardProbes_2023.pdf

11:50 Probing the short-length structure of the QGP with jet observables

High-energy partons are capable of triggering high-momentum exchanges with quark-like and gluon-like QGP quasi-particles that can be observed at sufficiently short length scales. In this work we present an implementation of a central aspect of this physics within the hybrid strong/weak coupling model. Interaction with the quasi-particles results in elastic, Moliere scatterings, leading to deflection of the direction of the jet parton that induced the process as well as the excitation of partons from the thermal medium that recoil after being kicked. Throughout the in-medium evolution, the system of jet partons and recoils, which might further re-scatter, inject energy and momentum into the QGP, producing wakes. Given the large impact of the wakes generated by the hydrodynamic response of the medium on jet observables, finding distinctive signatures of scattering off quasi-particles in the QGP is a challenging task. What makes the hybrid model particularly valuable as a tool for identifying observables that are more/less sensitive to scattering off quasi-particles and less/more sensitive to consequences of wakes in the QGP is that when we turn Moliere scattering off the model contains no effects of scattering — energy loss in the model arises from strongly coupled physics not from scattering. We can therefore use our investigation to suggest observables and strategies that may be followed with a view toward discerning separate consequences of the effects under consideration.

Sprecher: Prof. Krishna Rajagopal (MIT)

Rajagopal_MoliereSlides_HP2023.pdf

12:10 Search for medium effects using jets from bottom quarks in PbPb collisions a 5.02 TeV with CMS

Jet quenching, one of the signatures of the quark-gluon plasma, is a well established experimental phenomenon at RHIC and LHC. However, a detailed characterization of the expected dependence of jet-medium interactions on the flavor of the parton initiating the shower is yet to be settled. This talk presents the first b jet shapes measurements in 5.02 TeV PbPb and pp collisions collected by the CMS experiment. Comparisons made with jet shapes of inclusive jets, produced predominantly by light quarks and gluons, allow for experimental observations of the ``dead cone’’ effect in suppressing transverse momenta of constituents at small radial distance from the jet axis. A similar comparison for large distances provides insights on the role of parton mass in the energy loss and possible mass dependence of the medium response.

Sprecher: Lida Kalipoliti (LLR)

Kalipoliti_hp2023.pdf

12:30 → 14:00 Lunch

14:00 → 16:00 Parallel: Early-Time Dynamics & nPDFs

Sitzungsleiter: Guang-You Qin (Central China Normal University)

14:00 A novel saturation-based 3+1D initial state model for Heavy Ion Collisions

We present a new 3+1D resolved model for the initial state of ultrarelativistic Heavy-Ion collisions, based on the $k_\perp$-factorized Color Glass Condensate hybrid approach [1-4]. This new model responds to the need for a rapidity-resolved initial-state Monte Carlo event generator which can deposit the relevant conserved charges (energy, charge and baryon densities) both in the midrapidity and forward/backward regions of the collision.
This event-by-event generator computes the gluon and (anti-) quark phase-space densities using the IP-Sat model, from where the relevant conserved charges can be computed directly. In the present work we have included the leading order contributions to the light flavor parton densities. As a feature, the model can be systematically improved in the future by adding next-to-leading order calculations (in the CGC hybrid framework), and extended to lower energies by including sub-eikonal corrections the channels included. We present relevant observables, such as the eccentricities and flow decorrelation, as tests of this new approach.

References:
[1] O. Garcia-Montero, H. Elfner and S. Schlichting. In preparation.
[2]T. Lappi and S. Schlichting, Phys. Rev. D 97, 034034 (2018), arXiv:1708.08625 [hep-ph].
[3] T. Lappi and H. Mäntysaari, Phys. Rev. D 88, 114020 (2013), arXiv:1309.6963 [hep-ph]
[4] H. Mäntysaari, Scattering off the Color Glass Condensate, Ph.D. thesis, Jyvaskyla U. (2015), arXiv:1506.07313 [hep-ph].

Sprecher: Oscar Garcia-Montero (Universität Bielefeld)

HP2023_GarciaMontero.pdf

14:20 Illuminating early-stage dynamics of heavy-ion collisions through photons at RHIC BES energies

Heavy-ion collisions at $\sqrt{s_{\rm NN}} \sim 10$ GeV probes the QCD phase diagram at large baryon densities. However, because the longitudinal Lorentz contraction is small at these collision energies, understanding the dynamics during the early phase of the collision is essential for the subsequent modeling of the system evolution, and for constraining the QGP transport properties at finite baryon densities. Direct photons are multi-messengers in heavy-ion collisions, providing undistorted information about early-stage dynamics. In this talk, we model relativistic heavy-ion collisions at RHIC Beam Energy Scan energies with a hybrid dynamical approach which consists of a 3D-Glauber initial state followed by viscous hydrodynamics and finally by transport theory (MUSIC + UrQMD). Thermal photon emission takes into account the enhancement from finite baryon chemical potentials. We will show that direct photon spectra and their anisotropic flow coefficients have a strong sensitivity to the early stage of heavy-ion collisions and thus provide constraints on QGP dynamics complementary to those obtained from hadronic observables.

Sprecher: Chun Shen (WAYNE STATE UNIVERSITY)

photonBES.pdf

14:40 Dijet azimuthal correlations in p-p and p-Pb collisions at forward LHC calorimeters

I am going to present a state-of-the-art computation for the production of forward dijets in proton-proton and proton-lead collisions at the LHC, in rapidity domains covered by the ATLAS calorimeter and the planned FoCal extension of the ALICE detector. We use the small-x improved TMD (ITMD) formalism, together with collinearly improved TMD gluon distributions and full b-space Sudakov resummation, and discuss nonperturbative corrections due to hadronization and showers using the Pythia event generator. We observe that forward dijets in proton-nucleus collisions at moderately low pT are excellent probes of saturation effects, as the Sudakov resummation does not alter the suppression of the cross section.

Sprecher: Krzysztof Kutak (IFJ PAN)

HardProbes.pdf

15:00 Impact of fully coherent energy loss for nPDF extractions

Nuclear Parton Distribution Functions (nPDF) are an essential tool to predict hard QCD processes in nuclear collisions. Recently various nPDF sets have been extracted using heavy flavour data (D mesons, quarkonia) in pA collisions in the global fits. However, these measurements should be affected by fully coherent energy loss (FCEL) in nuclear matter, which entails a careful treatment in the nPDF determination. As a case study, we evaluate the impact of J/psi suppression data in pA collisions on gluon nPDF using Bayesian reweighing methods, with and without including FCEL. We show that these measurements dramatically shrink the uncertainty of gluon densities, as mentioned in earlier studies. The magnitude of gluon shadowing at small-x, however, is significantly reduced, by about factor of two, when FCEL is taken into account. This result highlights the importance of a careful separation between nPDF effects and energy loss processes and motivates future studies of global nPDF fits with a proper implementation of FCEL.

Sprecher: Tobie Avez (Subatech)

Hard Probes.pdf

15:20 Search for elliptic azimuthal anisotropies in photon-proton and pomeron-Pb interactions using rapidity gaps at pPb collisions with the CMS experiment

Since 2011 a wide variety of measurements suggest the existence of strong collectivity in collisions of small systems such as proton-proton (pp) and proton-nucleus (pPb) with hydrodynamic models and gluon saturation in the initial state as two theory alternatives showing consistency with the observations. These results raise the question as to whether such phenomena may be present in even smaller systems. Just recently ATLAS, ALEPH, and ZEUS collaborations have extended the studies to photon-Pb, electron-electron (ee), and electron-proton (ep) systems respectively. This talk will summarize the latest CMS results on the study of long-range particle correlations extended to photon-proton and pomeron-Lead interactions using pPb collisions at 8.16 TeV . Such interactions provide unique initial conditions with event multiplicity lower than in pp and pPb systems but comparable with ee and ep systems.

Sprecher: SUBASH CHANDRA BEHERA (Indian Institute of Technology Madras (IN))

TwopartCorr_HP_Subash.pdf

15:40 Determination of quark and gluon distributions in nuclei using correlated nucleon pairs

Analyzing data from nuclear lepton Deep-Inelastic Scattering, Drell- Yan processes, and W and Z boson production, we show that factorizing nuclear structure into quasi-free nucleons and universally modified close-proximity Short Range Correlated (SRC) nucleon pairs allows us to fully describe the quark-gluon structure of nuclei down to very-low momentum fractions. This is the first combined extraction of the universal distribution of quarks and gluons inside SRC pairs, and the nucleus-specific fraction of nucleons in SRC pairs. The extracted SRC fractions are in good agreement with previous nuclear structure calculations and measurements. At the same time the obtained nuclear PDFs are in very good agreement with fits using conventional framework of global nuclear PDF analysis. This extraction of nuclear structure information from quark-gluon distributions thus represents a significant development toward understanding the structure of nuclei in terms of their fundamental quark-gluon constituents.

Sprecher: Aleksander Kusina (Institute of Nuclear Physics PAN, Krakow)

kusina_HardProbes2023.pdf

14:00 → 16:00 Parallel: Heavy Flavours & Quarkonia

Sitzungsleiter: Joerg Aichelin (SUBATECH)

14:00 Measurements of $\rm{D}^0$ mesons production and collective flow with CMS at 5.02 TeV

The interaction of heavy quarks with the quark-gluon plasma (QGP) affects their azimuthal distribution and $p_{\rm{T}}$ spectrum, hence measurement of azimuthal anisotropy coefficients ($v_n$) and nuclear modification factors ($R_{\rm{AA}}$) of heavy flavor hadrons turns out to be an important probe of the QGP. However, simultaneous modeling of $v_n$ and $R_{\rm{AA}}$ is still challenging. This talk reports the first nonprompt $\rm{D}^0$ measurements of the azimuthal anisotropy elliptic ($v_2$) and triangular ($v_3$) coefficients in large systems, using !PbPb collisions at $\sqrt{s_\mathrm{NN}}= 5.02$ TeV, collected with the CMS apparatus. The measurements are performed as a function of transverse momentum, spanning 1--30 GeV /c, in three centrality classes, from central to midcentral collisions. Compared to the prompt $\rm{D}^0$ results, the nonprompt $D^0$ $v_2$ flow coefficients are systematically lower and show less dependence on $p_{\rm{T}}$ and centrality. An indication of non-zero $v_3$ coefficient of the nonprompt $\rm{D}^0$ is observed. A wide pT range enables the study of various flow generation mechanisms, like diffusion at low $p_{\rm{T}}$ and path-dependent parton energy loss at high $p_{\rm{T}}$. In addition, measurements of both prompt and nonprompt $D^0$ mesons cross sections in PbPb and pp collisions, as well as $R_{\rm{AA}}$, will be shown. The results will be compared to theoretical predictions.

Sprecher: Milan Stojanovic (Purdue University)

MStojanovic_HP2023_v2.pdf

14:20 heavy quark momentum diffusion coefficient in the hydrodynamizing plasma from effective kinetic theory

We compute the heavy quark momentum diffusion coefficient using effective kinetic theory for a system going through bottom-up isotropization until approximate hydrodynamization. We find that when matching the nonthermal diffusion coefficient to the thermal one for the same energy density, the observed deviations throughout the whole evolution are withing 30% from the thermal value. When matching for other quantities we observe considerably larger deviations. We also observe that the diffusion coefficient in the transverse direction dominates at large occupation number, whereas for an underoccupied system the longitudinal diffusion coefficient dominates. While the ratio of the diffusion coefficients does not follow the usual hydrodynamical attractor, we observe the emergence of a limiting weak coupling attractor governed by bottom-up scaling.

Sprecher: Jarkko Peuron (University of Jyväskylä)

HP23.pdf

14:40 PHENIX Measurements of Azimuthal Anisotropy of Light and Heavy Flavor Hadrons and J/Psi in Au+Au Collisions at Forward Rapidity

One of the most prominent features of the quark gluon plasma is its near-perfect fluid behavior. An important outstanding question is establishing the degree to which heavy flavor particles flow with the bulk system. Measurements of the Fourier coefficient v2 of light and heavy flavor hadrons and quarkonia can provide insight into the properties of the medium. At low transverse momentum (pT) the mass dependence of v2 is associated with the common flow velocity in the bulk system, whereas at higher pT path length and mass dependencies in the energy loss play a role. Additionally for J/Psi, the equilibration and recombination of charm quarks may produce azimuthal anisotropies. We will present new results measured with the PHENIX muon arms covering 1.2<|η|<2.2 using high statistics Au+Au dataset collected in 2014. The v2 of light hadrons and muons from heavy flavor decays are measured in the range 0.5<pT<7 GeV/c, and v2 of J/Psi in the range 0<pT<5 GeV/c. The results are compared to measurements at mid-rapidity. Different rapidities sample different initial and final state effects and have different densities of cc pairs, and therefore the produced particles may be subject to different pressure gradients and coalescence effects. The measurements will be compared to theoretical calculations.

Sprecher: Brandon Blankenship (Vanderbilt University)

Hard Probes 2023, FDraft PDF.pdf

15:00 D and B meson Suppression and Azimuthal Anisotropy in a Strongly Coupled Plasma at $\sqrt{s_{NN}}=5.5$ TeV

We present predictions for the suppression of D and B-mesons at $\sqrt{s}=5.5$ TeV at the LHC in Pb+Pb collisions. We assume that the QGP is strongly coupled, and show the centrality and momentum dependence of the nuclear modification factor at midrapidity. We quantify the systematic theoretical uncertainties associated with the mapping of parameters in $N=4$ SYM theory to QCD, as well as the momentum dependence of the diffusion coefficient in AdS/CFT. We also present results of the corresponding $v_2(p_T)$ for D and B-mesons describing this azimuthal anisotropy for central, semi-central and peripheral collisions. We show that the suppression and azimuthal anisotropy predictions are qualitatively consistent with LHC measurements. In addition, we show that coupling energy loss to flow increases $v_2$ substantially out to surprisingly large momenta, on the order of $\sim 25$ GeV/c, thus pointing to a possible resolution of the $R_{AA}$ and $v_2$ puzzle at intermediate $p_T$ for light hadrons.

Sprecher: Blessed Ngwenya (University of Cape Town)

Blessed-Hard_Probes_2023_Slides.pdf

15:20 Multi-scale evolution of heavy flavor in the QGP

Shower development dynamics for a jet traveling through the quark-gluon plasma (QGP) is a multi-scale process, where the heavy flavor mass is an important scale. During the high virtuality portion of the jet evolution in the QGP, emission of gluons from a heavy flavor is modified owing to heavy quark mass. In-medium stimulated radiation of heavy flavor is sensitive to microscopic processes (e.g. diffusion), whose virtuality dependence is phenomenologically explored in this study. In the lower virtuality part of shower evolution, i.e. when the mass is comparable to the virtuality of the parton, scattering and radiation processes of heavy quarks differ from light quarks. The effects of these mechanisms on shower development in heavy flavor tagged jets in the QGP is explored here. Furthermore, our multi-scale study examines dynamical pair production of heavy flavor (via virtual gluon splittings) and their subsequent evolution in the QGP, which is not possible otherwise. A realistic event-by-event simulation is performed using the JETSCAPE Framework. Energy-momentum exchange with the medium proceeds using a weak coupling recoil approach. Using leading hadron and open heavy flavor observables, differences in various heavy quark energy-loss mechanisms are explored, while the importance of heavy flavor pair production is highlighted along with future directions to study. Preliminary Bayesian constraint of parton momentum diffusion in the QGP is shown using light and heavy flavors.

Sprecher: Gojko Vujanovic ( University of Regina)

HP23_GV_v1.6.pdf

15:40 Prospects for open heavy-flavour and quarkonium measurements with NA60+

The high-intensity beams provided by the CERN SPS in a wide energy interval offer a unique opportunity to investigate the region of the QCD phase diagram at high baryochemical potential.
The NA60+ experiment, proposed for taking data with heavy-ion collisions at the SPS in the next years, has a strong potential of providing new insights into the QCD phase diagram via measurements of rare probes in a beam-energy scan of Pb$-$Pb and p$-$A collisions in the interval $\sqrt{s_{\rm NN}}=6-17$ GeV.

In this talk, the prospects for measurements of hidden and open charm will be presented.
Open charm hadrons will be measured from their decays into charged hadrons, which will be reconstructed from the tracks in the silicon detectors of the vertex telescope.
This will enable high-precision measurements of the yield of D$^0$, D$^+$, and D$_{\rm s}^+$ mesons, and of $\Lambda_{\rm c}^+$ baryons, thus allowing us to constrain the transport properties of the QGP and the charm-quark hadronisation.
Charmonium states, J/$\psi$ and $\psi$(2S), will be measured through dimuon decays reconstructed with the muon spectrometer.
By measuring the charmonium yield in p$-$A and Pb$-$Pb collisions at different collision energies, NA60+ will provide a unique opportunity to study the threshold energy for the onset of deconfinement.
The competitiveness and complementarity of NA60+ in the landscape of the experiments foreseen at other facilities in the next decade will be discussed.

Sprecher: Roberta Arnaldi

HP23_Arnaldi.pdf

14:00 → 16:00 Parallel: Jets and their modification in QCD Matter: I

Sitzungsleiter: Brian Cole (Columbia University)

14:00 Partonic Critical Opalescence and Its Impact on the Jet Quenching Parameter

Jet quenching parameter $\hat{q}$ is essential for characterizing the interaction strength between jet partons and nuclear matter. Based on the quark-meson (QM) model, we develop a new framework for calculating $\hat{q}$ at finite chemical potentials, in which $\hat{q}$ is related to the spectral function of the chiral order parameter. A perturbative calculation up to the one-loop order indicates that the momentum broadening of jets is enhanced at both the high temperature and high chemical potential, and approximately proportional to the parton number density in the partonic phase. We further investigate the behavior of $\hat{q}$ in the vicinity of the critical endpoint (CEP) by coupling our calculation with a recently developed equation of state that includes a CEP in the universality class of the Ising model, from which we discover the partonic critical opalescence (PCO) -- a prominent enhancement of the momentum broadening of jets near CEP, contributed by the scatterings via the $\sigma$ exchange process. Hence, for the first time, jet quenching is connected with the search of CEP.

Sprecher: Feng Li (Lanzhou University)

PartonicCriticalOpalescenceforHardProbe2023.pdf

14:20 Impact of pre-equilibrium dynamics on jet quenching observables

Given recent works showing jet quenching’s sensitivity to the dynamics of the pre-hydrodynamic phase of heavy-ion collisions, addressing medium-induced radiation in the initial stages becomes crucial. In this talk, we derive the BDMPS-Z emission spectrum off a hard parton accounting for additional medium-induced emissions arising from its vacuum propagation in the pre-hydrodynamics phase. By comparing this set-up with those where the emitter is created inside the medium, but with different starting points, we isolate the contribution of this initial radiation. We then analyze the impact that this extra radiation may have in the determination of the nuclear modification factor and high-$p_T$ azimuthal asymmetry. Our findings show that replacing in-medium propagation by vacuum propagation prior to hydrodynamization leads to an increase in the high-$p_T$ $v_2$. However, this increase in the asymmetry is smaller than the one obtained when setting the parton to be created at the hydrodynamization time.

Sprecher: Marcos Gonzalez Martinez (IGFAE - Universidade de Santiago de Compostela (ES))

GonzalezMartinezMarcos_HP2023.pdf

14:40 First measurements of in-jet fragmentation and correlations of charmed mesons and baryons in pp collisions with ALICE

Fragmentation functions are one of the key components of the factorisation theorem used to calculate heavy-flavour hadron production cross sections. The non-perturbative nature of fragmentation functions necessitates their constraint through experimental measurements, commonly performed in the clean environments of $\rm{e}^{+}\rm{e}^{-}$ and $\rm{ep}$ collisions. However, recent measurements of charm hadron spectra and of the ratios of charmed-hadron abundances in pp collisions have questioned the universality of fragmentation functions between leptonic and hadronic collision systems in the baryon sector. In this talk, we present measurements of differential observables that also consider the surrounding hadronic density in addition to the heavy-flavour hadron itself. These measurements provide additional information to the previously reported baryon-to-meson results and allow to obtain a closer connection to the charm fragmentation functions. We report the fraction of longitudinal momentum carried by $\rm{D}^{0}$ and $\rm{D}_{s}^{+}$ mesons as well as $\Lambda_{c}^{+}$ baryons. We also report correlations between heavy-flavour decay electrons and charged particles in pp and p-Pb collisions, as well as azimuthal-angle correlations of $\Lambda_{c}^{+}$ baryons with charged particles in pp collisions, which provide quantitative access to the angular profile, $p_{\rm T}$ and multiplicity distributions of the jets produced by the heavy-quark fragmentation.

Sprecher: Antonio Palasciano (Università & INFN, Bari)

HP23_APalasciano.pdf

15:00 Jet suppression and azimuthal anisotropy at RHIC and LHC

Jets are multi-partonic systems that develop before interactions with the QGP set in and lead to energy loss and modifications of their substructure. Jet modification depends on the degree to which the medium can resolve the internal jet structure that is dictated by the physics of coherence governed by a critical angle $\theta_c$. Using resummed quenching weights that incorporate the IOE framework for medium-induced radiation and embedding the system into a realistic heavy-ion environment we compute the $R$ dependence of jet suppression, both at RHIC and the LHC. At RHIC kinematics we see a very mild $R$-dependence for the range of $R$ studied, similar to what was found at the LHC. We also present results for the jet azimuthal anisotropy $v_2$ as a function of $R$. We observe that as centrality is decreased, $v_2$ for moderate $R$ jets sequentially collapse towards the result for small $R=0.1$. The reason of this sequential grouping is the evolution of $\theta_c$ with centrality due to its strong dependence on the in-medium traversed length. For those jets with $R>\theta_c$, traversing shorter lengths within the medium will make a larger difference than for those jets with $R<\theta_c$, since the size of the resolved phase-space over which quenching weights are resummed will be reduced. For this reason, $v_2(R)$ is quite sensitive to the typical value of $\theta_c$ at a given centrality.

[1] Y. Mehtar-Tani, D. Pablos, K. Tywoniuk. Phys.Rev.Lett. 127 (2021) 25, 252301

Sprecher: Dr. Konrad Tywoniuk

HP2023_Tywoniuk.pdf

15:20 Determining the onset of color coherence with energy correlators

We present a new approach to jet substructure in heavy-ion collisions based on the study of correlation functions of energy flow operators (energy correlators). This approach is based on the insight that the dynamics of the QGP is imprinted at specific time scales in the jet, which will be reflected as changes in the shape of the correlator. We analyze the two-point correlator of an in-medium massless quark jet within three jet quenching formalisms: BDMPS-Z with the harmonic oscillator approximation, BDMPS-Z with a Yukawa (Gyulassy-Wang) parton-interaction model, and the first opacity GLV framework. We show that the spectra of correlation functions is sensitive to color coherence, which allows us to robustly identify the resolution scale of the QGP: the energy scale at which in-medium emissions start to be resolved by the QGP.

Sprecher: Fabio Dominguez (IGFAE, Universidade de Santiago de Compostela)

DominguezHP2023.pdf

14:00 → 16:00 Parallel: Jets and their modification in QCD Matter: II

Sitzungsleiter: Prof. Krishna Rajagopal (MIT)

14:00 Unbiased quantification of jet energy loss

Bin migration effects hinder a direct connection between the nuclear modification factor $R_{AA}$ and the energy lost by jets. $R_{AA}$ compares yields of jets, in pp and AA collisions, that are reconstructed with the same $p_T$ and is thus biased by the steeply falling jet spectrum. To mitigate these effects, Brewer et al. [1] introduced a novel observable to directly quantify average jet energy loss ($Q_{AA}$), given by the ratio of the transverse momenta that correspond to the same probability quantiles in pp and AA.
This work reinforces the claim that $Q_{AA}$ ratio is a reliable proxy for jet energy loss and, by using it, it shows that energy loss decreases with increasing jet radius when QGP response, as implemented in the JEWEL event generator, is accounted for. Further, our results establish that, contrary to recent claims, the difference in $R_{AA}$ between dijet and boson-jet events is dominated by differences in the spectral shape, leaving the colour charge of the jet initiating parton with a minor role to play.

[1] Brewer, J., Milhano, J. G., & Thaler, J. (2019). Sorting out quenched jets. Physical Review Letters, 122(22), 222301.

Sprecher: Herr João M. Silva (LIP - Lisboa / ULisboa - IST)

JMSilva_HP2023.pdf

14:20 Jet Measurements with PHENIX

Reference measurements in p+p collisions are crucial for understanding jet quenching. PHENIX has a suite of new jets measurements in p+p collisions: fragmentation function, transverse momentum, jt, distribution, the radial profile, and splitting functions.

Jet quenching effects can also be studied with high momentum hadrons and two-particle correlations. The distribution of hadrons opposite a high pt $\pi^{0}$ or photon in Au+Au collisions, reveals how the distribution of hadrons within the opposing jet is modified compared to that in p+p collisions. PHENIX has measured $\pi^{0}$-hadron and $\gamma$-hadron angular correlations in Au+Au and p+p collisions with detailed measurements that probe the angular distribution of the modifications.

To fully quantify the quenching effects in heavy ion collision, we must also understand potential modifications in smaller collision systems. Previous PHENIX measurements of jets and $\pi^{0}$s in d+Au collisions revealed possible modifications when dividing the measurements into different event multiplicity or centrality classes. Updated reconstructed jet measurements and the use of direct photons to study possible biases in the event
selection suggest that while peripheral d+Au collisions are consistent with expectations from p+p collisions, some suppression in the most central d+Au events may still exist.
The talk will summarize the latest PHENIX jet-related measurements in p+p, d+Au, and Au+Au collisions.

Sprecher: Julia Velkovska (Vanderbilt University)

Velkovska_HP2023

14:40 Precise description of medium-induced emissions

We study jet fragmetation via final-state parton splittings in the medium. These processes are usually calculated theoretically by invoking one or two approximations: the large-Nc and the eikonal approximations. We want to develop methods to do the calculations without using these approximations, and to quantify the error that is introduced by employing them.
As partons go through the medium their color continuously rotates, an effect that is encapsulated in a Wilson line along their trajectory. When calculating observables, one typically has to calculate correlators of several Wilson lines. This is usually dealt with in the literature by invoking the large-Nc limit. In an earlier work we showed how correlators of multiple Wilson lines appear, and developed a method to calculate them numerically to all orders in Nc.
However, in our previous paper we made use of the eikonal approximation, meaning that the partons are assumed to travel in straight lines through the medium. This might not be a good approximation for soft and imbalanced splittings, where the produced partons can be kicked around by the medium. We show how the full problem can be transformed into solving a set of coupled Schrödinger equations, with the aforementioned Wilson line correlators acting as the potential term. This system of differential equations is then solved numerically. These results are relevant for high-pT jet processes, multi-gluon emissions in the QGP and initial stage physics at the LHC.

Sprecher: Johannes Hamre Isaksen (University of Bergen)

isaksen_hard_probes.pdf

15:00 Medium effects on Hadrons and Jets in $\sqrt{s_{\mathrm{NN}}}=200\hbox{ GeV}$ Isobar Collisions at STAR

Partonic scatterings with large momentum transfer occur before the formation of the quark-gluon plasma (QGP) in heavy-ion collisions, resulting in collimated collections of hadrons known as jets. As a jet traverses and interacts with the QGP medium, it loses energy via collisional and radiative processes, known as jet quenching. The magnitude of the energy loss can be quantified by the ratio of hadron or jet yields in A+A and p+p collisions, know as the nuclear modification factor ($R_{\rm{AA}}$). The high-statistics 2018 STAR isobar data, comprised of Zr+Zr and Ru+Ru collisions, offer the opportunity to study the system size dependence of nuclear modification for hard probes. A measurement of the inclusive charged hadron $R_{\rm{AA}}$ differentially with the average number of participants ($\left\langle N_{\mathrm{part}}\right\rangle $) in the isobar collisions will be presented with comparisons to both smaller and larger sized systems. In addition to studying the total energy loss via $R_{\mathrm{AA}}$, the path-length dependence of jet quenching processes can be studied by measuring the azimuthal anisotropy of jet yields relative to the event plane, quantified by the second-order Fourier coefficient $v_2^{\rm{jet}}$. A finite $v_2^{\rm{jet}}$ is expected in mid-central heavy-ion collisions where a highly ellipsoidal QGP medium is formed, resulting in jets traversing in-plane interacting with less medium than those out-of-plane. Measurements of $v_2^{\rm{jet}}$ in isobar collisions spanning multiple jet resolutions will be presented. Ongoing work to use event shape engineering to more precisely control the path length of the initiating partons will also be shown.

Sprecher: Tristan Protzman (Lehigh University)

Protzman_HP23_Talk_HP_As_Presented_.pdf

15:20 Thermalization of a jet wake in QCD kinetic theory

We study the energy deposition of a high-momentum parton traveling through a Quark-Gluon Plasma using QCD kinetic theory. We show that the energy is first transported to the soft sector by collinear cascade and then isotropised by elastic scatterings. Remarkably, we find that the jet wake can be well described by a thermal distribution function with angle-dependent temperature. This could be used for effective phenomenological descriptions of jet thermalization in realistic heavy-ion collision simulations.

Sprecher: Fabian Zhou (ITP Heidelberg)

HP2023_Fabian_Zhou.pdf

15:40 Effects of multi-scale jet-medium interactions on jet substructures

We investigate how the scale-dependent jet-medium interactions affect the jet substructure observables in heavy-ion collisions via event-by-event Monte Carlo simulation using the JETSCAPE framework. Jets are dynamic probes with varying virtualities and energies of partonic constituents in their shower evolution. The various internal medium structures involved in interactions at different scales of the jet parton’s virtuality and energy are encoded in the modification of reconstructed jets. Recently, we found that the reduction of jet-medium interaction at the early high-virtuality stage, where the medium is resolved at a very short distance scale and appears more dilute [1], is the key to explaining the different trends in reconstructed jet RAA and single particle RAA in a unified manner [2].
In this study, we focus on jet substructure observables to explore further details of the scale dependence by performing numerical simulations with explicit virtuality dependence in the jet-medium interaction rate within the MATTER+LBT setup of the JETSCAPE framework. We compare results for the Soft Drop groomed observables and jet fragmentation function to data and demonstrate the significant effect of the reduction of jet-medium interaction at the early high-virtuality stage.
[1] Amit Kumar, Abhijit Majumder, and Chun Shen, Phys. Rev. C, 101(3):034908, 2020.
[2] JETSCAPE, arXiv:2204.01163 [hep-ph].

Sprecher: Yasuki Tachibana (Akita International University)

tachibana_HP23.pdf

Donnerstag, 30. März

09:00 → 10:40 Parallel: Electromagnetic & Electroweak Probes

Sitzungsleiter: Axel Drees (Stony Brook University)

09:00 Direct-photon production and HBT correlations in Pb–Pb collisions at 5.02 TeV with the ALICE experiment

Measurements of direct photons can provide valuable information on the properties and dynamics of the quark-gluon plasma (QGP) by comparing them to model calculations that describe the whole evolution of the system created in heavy-ion collisions, from the initial conditions to the pre-equilibrium, QGP, and hadronic phases. In the ALICE experiment, photons can be reconstructed via conversion photons using the excellent tracking capabilities, or via direct measurements in the two different types of calorimeters. Combining these different methods we can measure the direct-photon production from lower momentum of 0.4 GeV/c. Exploring the Hanbury Brown and Twiss (HBT) correlation measurement, we can correlate one conversion photon and one calorimeter photon with near-zero opening angle.
In this talk, we will present the first measurements in selected centrality classes of the direct-photon production in Pb—Pb collisions at 5.02 TeV collision energy, as well as the measurements of the photon HBT correlation. The ALICE upgrades will allow us to measure direct photons in the upcoming Run 3 of the LHC and further improve the direct-photon measurements in the ALICE experiment.

Sprecher: Ana Marin (GSI)

HP2023_Marin.pdf

09:20 Vector and Axial-Vector Mesons in Nuclear Matter

We present recent results on the in-medium spectral function of the rho(770) vector meson and the a1(1260) axial-vector meson in nuclear matter, as well as on the resulting thermal dilepton rate. As an effective description of the thermodynamics and the phase structure of nuclear matter we use a chiral baryon-meson model, taking into account the effects of fluctuations from scalar mesons, nucleons, and vector mesons within the Functional Renormalization Group (FRG) approach. Our results show strong modifications of the spectral functions in particular near the chiral critical endpoint which suggest an enhanced dilepton yield at lower energies. Such an enhancement is also found in GiBUU transport simulations for C+C at 1A GeV when including effects of chiral symmetry restoration in the kinetic equations for baryon propagation. Our results may therefore well be of relevance for electromagnetic rates in heavy-ion collisions and help to identify phase transitions and the critical endpoint.

Sprecher: Dr. Ralf-Arno Tripolt (Justus Liebig University Giessen)

Tripolt_HP_2023.pdf

09:40 Measuring pressure anisotropy of the quark-gluon plasma through photon polarization

Photons are radiated throughout heavy-ion collisions, including from the hot and dense quark-gluon plasma (QGP). In this talk, we consider the polarization of QGP photons. The polarization gives detailed information about how the pressure anisotropy of the QGP medium evolves and thus how the medium isotropizes during the initial stages of collisions. We calculate for the first time the emission of polarized photons through quark-antiquark pair annihilation and bremsstrahlung in an anisotropic QGP medium. Our calculation includes the Landau-Pomeranchuk-Migdal effect fully. We show that the polarization goes directly as the anisotropy of the soft gluon cloud radiated by quarks and gluons and thus measures pressure anisotropy. Finally, we discuss the size of these effects in heavy-ion collisions and the feasibility of measuring the photon polarization.

Sprecher: Sigtryggur Hauksson

HP23_hauksson_2.pdf

10:00 Pre-equilibrium photon production in QCD Kinetic Theory

We use QCD kinetic theory to compute photon production in the chemically equilibrating out-of-equilibrium Quark-Gluon Plasma created in the early stages of high-energy heavy-ion collisions. We compare the non-equilibrium rates to the production in a thermal QGP and extract the dependence of pre-equilibrium photon production on the kinetic and chemical equilibration time. This allows us to include realistic pre-equilibrium photon production in heavy-ion collisions.

Sprecher: Philip Plaschke

HP23Plaschke.pdf

10:20 Characterising the hot and dense fireball with virtual photons at HADES

Electromagnetic probes ($\gamma, \gamma^{\ast}$) offer a unique opportunity to study the conditions during heavy-ion collisions. They are produced throughout the whole evolution of the colliding system and can penetrate the strongly interacting medium to bring direct information from their origins to the detector. In this manner, it is possible to not only probe freeze-out, but also earlier stages of maximum temperature and density.

In this contribution, we present measurements of dielectrons from Ag+Ag collisions, collected at the High-Acceptance-DiElectron-Spectrometer (HADES), at $\sqrt{s_{NN}}=2.55$ GeV and $\sqrt{s_{NN}}=2.42$ GeV. A particular focus is set on collectivity studies with a multidifferential analysis of the directed flow $v_{1}$ and elliptic flow $v_{2}$ in terms of centrality, rapidity, transverse momentum and invariant mass.

Sprecher: Niklas Schild (TU Darmstadt)

HardProbes_NiklasSchild_2023.pdf

09:00 → 10:40 Parallel: Heavy Flavours & Quarkonia

Sitzungsleiter: Prof. Pol-Bernard Gossiaux (IMT Atlantique)

09:00 Quarkonium polarization in pp and Pb-Pb collisions from ALICE

Polarization measurements represent an important tool for the understanding of particle production mechanisms occurring in proton–proton collisions. When considering heavy-ion collisions, quarkonium polarization could also be used to investigate the characteristics of the hot and dense medium, the quark-gluon plasma (QGP) created at LHC energies. It has been hypothesized that quarkonium states could be polarized by the strong magnetic field, generated in the early phase of the evolution of the system, and by the large angular momentum of the medium in non-central heavy-ion collisions. This kind of information can be assessed by defining an ad hoc reference frame where the quantization axis is orthogonal to the event plane of the collision. In this contribution, the new published result of J/$\psi$ polarization with respect to a quantization axis orthogonal to the event-plane in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV will be presented. The $\it{p}_{T}$-differential measurement was performed at forward rapidity (2.5 $<\it{y}<$ 4) and the results will be shown for different centrality classes. The preliminary $\Upsilon$(1S) polarization analysis, as well as the status of the new J/$\psi$ and $\psi$(2S) polarization analyses in pp collisions at $\sqrt{s}$ = 13 TeV as a function of the transverse momentum will also be discussed.

Sprecher: Andrea Ferrero (Université Paris-Saclay (FR) and CEA-IRFU-DPhN)

Unknown-2.pdf

09:20 Heavy quarks probe the equation of state of QCD matter in heavy-ion collisions

We show for the first time that heavy flavor quenching and flow can be utilized to probe the equation of state (EoS) of quark-gluon plasma (QGP) produced in relativistic heavy-ion collisions. Based on our quasi-particle linear Boltzmann transport (QLBT) model that is coupled to a (3+1)-dimensional viscous hydrodynamic simulation of the QGP and a hybrid fragmentation-coalescence approach for heavy flavor hadronization, we perform a detailed analysis on the $D$ meson $R_{\rm AA}$ and $v_2$ data at RHIC and the LHC using the state-of-the-art Bayesian statistical framework. A simultaneous constraint on the QGP EoS and the heavy quark transport coefficient is achieved, both consistent with the lattice QCD results.

[1] Feng-Lei Liu, Wen-Jing Xing, Xiang-Yu Wu, Guang-You Qin, Shanshan Cao, Xin-Nian Wang, Eur.Phys.J.C 82 (2022) 4, 350.
[2] Feng-Lei Liu, Xiang-Yu Wu, Shanshan Cao, Guang-You Qin, Xin-Nian Wang, to be submitted.

Sprecher: Xiang-yu Wu (Central China Normal University)

qlbt_hp2023.pdf

09:40 $\psi$(2S) production in Pb-Pb in ALICE

Charmonium production is a probe sensitive to deconfinement in nucleus-nucleus collisions. The production of J/$\psi$ via regeneration within the QGP or at the phase boundary has been identified as an important ingredient for the description of the observed J/$\psi$ nuclear modification factor at the LHC. The $\psi$(2S) production relative to J/$\psi$ is a possible discriminator between the two different scenarios. Studies of $\psi$(2S) production in central nucleus-nucleus collisions at low transverse momentum ($p_{\rm T}$) are crucial, in particular at the LHC, where regeneration might be dominant. For the first time, a significant $\psi$(2S) signal is extracted in such a kinematic region at forward rapidity in the dimuon decay channel. This measurement relies on the recently published $\psi$(2S) cross section measured in pp collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV with an unprecedent precision compared to previous ALICE results.
In this contribution, we present newly published results on the $\psi$(2S)-to-J/$\psi$ (double) ratio and the $\psi$(2S) nuclear modification factor in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV. Results are reported as a function of centrality and $p_{\rm T}$ in the region $p_{\rm T} < $ 12 GeV/c and are compared to available NA50 and CMS measurements. Comparisons to transport and statistical hadronization model predictions are also provided to shed light on charmonium states recombination mechanism.

Sprecher: Victor Feuillard

VictorFeuillard_HP2023Talk_V5.pdf

10:00 J/psi production in Ru+Ru and Zr+Zr collisions at sqrt{s_{NN}} = 200 GeV with the STAR experiment

J/$\psi$ is an important probe to study the properties of the quark-gluon plasma (QGP) created in heavy-ion collisions. Measurements of J/$\psi$ yield suppression in Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 200 GeV suggest that J/$\psi$ production in heavy-ion collisions is affected by the interplay of several effects, such as dissociation, regeneration in the QGP, and the cold nuclear matter effects. Since all these effects are expected to strongly depend on the system size, varying the collision system provides a promising approach to study J/$\psi$ production in heavy-ion collisions.

In 2018, the STAR experiment collected a high statistics sample of isobaric collisions ($^{96}_{44}Ru$+$^{96}_{44}Ru$ and $^{96}_{40}Zr$+$^{96}_{40}Zr$) at $\sqrt{s_\mathrm{NN}}$ = 200 GeV. In this talk, we will present the precision measurements of inclusive J/$\psi$ production yields as well as its elliptic flow from this data sample. These results will be compared to the similar measurements in Au+Au and Cu+Cu collisions at $\sqrt{s_\mathrm{NN}}$ = 200 GeV and physics implications will also be discussed.

Sprecher: Yan Wang (University of Science and Technology of China), Leszek Kosarzewski

HP_slide.pdf

10:20 Studies of heavy quark dynamics using B mesons with the CMS detector

Heavy quarks are one of the most important probes to study the properties of quark-gluon plasma (QGP). We present new results on nuclear modification factors of $\rm{B}_{\rm{s}}^{0}$ and $\rm{B}^{+}$ mesons in pp and PbPb collisions at 5.02 TeV, using data recorded with the CMS detector in 2017 and 2018. The reported B meson nuclear modification factors over an extended transverse momentum range will provide important information about the diffusion of beauty quarks and the flavor dependence of in-medium energy loss. In addition, understanding the hadronization mechanism is crucial for extracting the transport properties of the QGP. The $\rm{B}_{\rm{s}}^{0}/\rm{B}^{+}$ yield ratio in pp and PbPb can thus shed light on beauty hadronization mechanisms from small to large systems and on the relevance of parton recombination in the medium. We also report the first observation of the $\rm{B}_{\rm{c}}^{+}$ meson in nucleus-nucleus collisions. Given the low production cross-section in pp collisions, its production could be significantly enhanced by the recombination of beauty with charm quarks present in the hypothesized medium, providing additional insights into the recombination mechanism.

Sprecher: Tzu-An Sheng (MIT)

hp2023_qm.pdf

09:00 → 10:40 Parallel: Jets and their modification in QCD Matter: I

Sitzungsleiter: Leticia Cunqueiro

09:00 Systematic exploration of multi-scale jet substructure in $p+p$ collisions at $\sqrt{s}=200$ GeV by the STAR experiment

Jets are multi-scale objects that connect asymptotically free partons to confined hadrons. Jet substructure measurements in vacuum provide essential insight into the parton evolution and the ensuing non-perturbative processes.

In this study, we use the SoftDrop grooming technique, based on the angular-ordered Cambridge/Aachen reclustering algorithm, to probe correlations between jet substructure variables. This technique provides a correspondence between experimental observables and QCD splitting functions in vacuum. Corrections for detector effects are carried out utilizing either a three dimensional correction procedure or a machine learning based framework called MultiFold, with the latter retaining the correlations across jet substructure observables.

In particular, we explore ensemble level and jet-by-jet correlations between variables such as the shared momentum faction ($z_{\text{g}}$), splitting scale ($k_{\text{T}}$), groomed mass fraction ($\mu$), jet charge ($Q$, sensitive to the hadronization process) and groomed jet radius ($R_{\text{g}}$) for jets of varying momenta and radii in $p$+$p$ collisions at $\sqrt{s} = 200$ GeV using the STAR detector. To study the evolution along the jet shower, we present splitting observables at the first, second, and third splits along the jet shower for various jet and initiator prong momenta. Finally, the measurements are compared to leading order Monte Carlo models, such as PYTHIA 6, PYTHIA 8 and HERWIG.

Sprecher: Monika Robotková

HardProbes_2023_Robotkova.pdf

09:20 Exploring the time axis within medium-modified jets

The fast evolution of the QGP makes its interaction with jets an inherently time-dependent process. However, this crucial dimension is missing from current jet quenching measurements, which hence provide a mere average quantification of the medium properties. In this talk, we propose that jet substructure observables allow access to the QGP time structure. By identifying the recursive steps of a novel jet clustering algorithm (the tau-algorithm) with the sequence of branchings of the parton shower, we obtain an adequate proxy for a time axis within the medium. This technique enables us to label jets according to their formation time and select populations with enhanced sensitivity to quenching effects. By analysing the subsequent splitting, we also explore the possibility of quantifying time-differential properties of the medium. Moreover, we show how this method minimizes the biases stemming from pt- or DeltaR-based selections. The techniques presented here constitute a definite step towards QGP tomographic measurements.

Sprecher: Pablo Guerrero-Rodríguez (LIP)

HP2023_Pablo.pdf

09:40 Parton cascades at DLA: the role of the evolution variable

While experimental studies on jet quenching have achieved a large sophistication, the theoretical description of this phenomenon still misses some important points. One of them is the interplay of vacuum-like emissions, usually formulated in momentum space, with the medium induced ones that demand an interplay with a space-time picture of the medium and thus must be formulated in position space. A unified description of both vacuum and medium-induced emissions is lacking. In this work, we compute the tree-level probability of a double gluon emission in vacuum, and identify the enhanced phase-space regions for each diagram, corresponding to different configurations of the parton cascade. This calculation provides a parametric form for the formation times associated with each diagram, highlighting the equivalence of various ordering variables at double logarithmic accuracy. This equivalence is further explored by building a toy Monte-Carlo parton shower ordered in formation time, virtuality, transverse momentum, and angle. Aiming at a link with jet substructure, we compute the Lund Plane distributions and trajectories for each ordering prescription. We also compute the distributions in number of splittings and final partons, with the goal of clarifying the differences to be expected from the different ordering variables and the vetoes that must be implemented at Monte Carlo level to conserve energy-momentum, which turn out to have a sizable influence on the shower's evolution.

Sprecher: André Cordeiro (Laboratório de Instrumentação e Física Experimental de Partículas)

ACordeiro-HP23.pdf

10:00 Charge enhancement of parton showers in QCD plasmas

By scattering with the medium, partons produced by an in-medium shower can change their flavor. At these intermediate energy scales, the rate of gluon conversion to quarks and antiquarks can be more than double the reverse process of quark conversion. Consequently, interactions with the medium lead to a ring of fermions around the hard parton [1]. We present estimates of the range of angles and times where these charge/baryonic rings appear in the angular structure of jets. We discuss the consequences of this dramatic change in the baryon content of the jets, due to the presence of the medium, and how it may contribute to the baryon enhancements observed at intermediate $p_T$.

[1]- C. Sirimanna et al., arXiv:2211.15553

Sprecher: Shanshan Cao (Shandong University)

HP2023-Shanshan.pdf

10:20 Strong constraints on jet modification in centrality-dependent p+Pb collisions by ATLAS

Small systems such as pp or p+Pb collisions exhibit evidence of collective behavior strikingly similar to that in Pb+Pb collisions. However, while jet quenching is readily observed in Pb+Pb collisions, no evidence has been found in small systems to date, raising fundamental questions about the nature of the system created in these collisions. This talk reports a measurement by the ATLAS experiment at the LHC which sets new, precise constraints on the possible amount of jet modification in central p+Pb events. To avoid possible biases on the centrality classification of p+Pb events, the collision centrality is categorized by the energy deposited by forward neutrons from the struck nucleus in the Zero Degree Calorimeter (ZDC). The measurement reports the yield of charged hadrons near and opposite in azimuth to reconstructed jets in p+Pb and pp collisions at 5.02 TeV. The ratio between p+Pb and pp, called the $I_{\mathrm{pPb}}$, is consistent with unity within a few percent for hadrons with $p_{\mathrm{T}} > 4$ GeV at all centralities. These data provide new, strong constraints and can be used to set a quantitative limit on jet modification in central p+Pb collisions within a simple model.

Sprecher: Jamie Nagle (University of Colorado Boulder)

nagle_hp_atlas_pbjetquenching_2023.pdf

09:00 → 10:40 Parallel: Jets and their modification in QCD Matter: II

Sitzungsleiter: Mateusz Ploskon

09:00 A unified picture of medium-induced emissions

We revisit the picture of jets propagating in the quark-gluon plasma. In addition to vacuum radiation, related to the high initial virtuality, jet particles scatter on the medium constituents resulting in induced emissions. Analytical approaches to resumming these interactions have traditionally dealt separately with multiple, soft, or rare, hard scatterings. A full resummation has so far only been available using numerical methods. We recently achieved analytical control in the full phase space [1]. To this aim, we extended existing resummation schemes to the Bethe-Heitler regime, to cover emissions from early to late times, and from hard splittings to emissions below the thermal scale. Based on the separation of scales, a new space-time picture emerges: at early times, jets start building from both, vacuum and rare, hard scattering-induced emissions. At a later stage, determined by a resolution criterion, these emissions initiate a turbulent cascade that rapidly degrades energy down to, and including the Bethe-Heitler regime. We quantify the impact of such an improved picture, compared to the current factorization that includes only soft scatterings, by analytical and numerical methods for different jet observables. We introduce the concept of accuracy for quenched observables for the first time and show how it improves jet quenching from small to large systems and serves upgrades for Monte Carlo generators.

[1] J. H. Isaksen, A. Takacs and K. Tywoniuk, arXiv:2206.02811.

Sprecher: Adam Takacs (University of Bergen)

Adam_Takacs_HardProbes_2023.pdf

09:20 Hybrid Hadronization of Jet Showers from e+e- to AA with JETSCAPE

In this talk we review jet production in a large variety of collision systems using the JETSCAPE event generator and Hybrid Hadronization. Hybrid Hadronization combines quark recombination, applicable when distances between partons in phase space are small, and string fragmentation appropriate for dilute parton systems. It can therefore smoothly describe the transition from very dilute parton systems like e+e- to full AA collisions.
We test this picture by using JETSCAPE to generate jets in various systems. Comparison to experimental data in e+e- and pp collisions allows for a precise tuning of vacuum baseline parameters in JETSCAPE and Hybrid Hadronization. Proceeding to systems with jets embedded in a medium, we study in-medium hadronization for jet showers. We quantify the effects of an ambient medium, focusing in particular on the dependence on the collective flow and size of the medium. Our results clarify the effects we expect from in-medium hadronization of jets on observables like fragmentation functions, hadron chemistry and jet shape.

Sprecher: Cameron Parker (Texas A&M University)

HP2023-cameron-parker.pdf

09:40 Measurements of semi-inclusive $\gamma$+jet and hadron+jet distributions in heavy-ion collisions at $\sqrt{s_\mathrm{NN}}$ = 200 GeV with STAR

We present measurements of the semi-inclusive distribution of charged-particle jets recoiling from $\gamma$ and $\pi^{0}$ triggers in $p$+$p$ and central Au+Au collisions, and from charged hadron triggers in smaller collision systems (Ru+Ru and Zr+Zr) at $\sqrt{s_\mathrm{NN}}$ = 200 GeV by STAR. The large uncorrelated background in heavy-ion collisions is removed using the event mixing technique, enabling systematically well-controlled measurements at very low jet transverse momentum $p_\mathrm{T}^\mathrm{jet}$ and large jet radius R. We report corrected distributions as a function of both $p_\mathrm{T}^\mathrm{jet}$ and recoil azimuthal deflection with respect to trigger axis for R = 0.2 and 0.5 jets in p+p and Au+Au collisions. These measurements probe medium-induced jet yield suppression, intra-jet broadening, and jet acoplanarity, as well as their dependence on the color charge in heavy-ion collisions. We also present comparisons to theoretical calculations incorporating Sudakov broadening in vacuum and jet quenching in the medium. Jet yield suppression in central to peripheral collisions is measured in Ru+Ru and Zr+Zr collisions to study the system size dependence of jet energy loss. These together provide a multi-messenger study of the physical processes driving the jet quenching phenomenon.

Sprecher: Yang He (Shandong University), Maowu Nie

HP2023_20230312_v4.pdf

10:00 Jet shape depending on the gradient of jet transport coefficient in heavy-ion collisions

Jet shape is studied with a linear Boltzmann transport model for event-by-event simulations of photon-tagged jets in heavy-ion collisions. The transverse momentum asymmetry $A_\perp$ is shown to increase with the initial transverse position when the gradient of jet transport coefficient $\hat{q}$ increases until at the edge of the nonuniform medium. On one hand,the shape of the photon-tagged jet selected by the smaller $A_\perp$ events is "fatter" for the transverse momentum distribution inside the jet due to stronger jet quenching. On the other hand, the jet shape with higher $p_T^{jet}$ is "thinner" due to surface emission of the initial jets. Our numerical results show that the different choices for both final observables $A_\perp$ and $p_T^{jet}$ demonstrate different initial jet creation cites and therefore different jet shapes depending on the gradient of $\hat{q}$ .

Sprecher: Han-Zhong Zhang (CCNU)

hp2023-zhz.pptx

10:20 Charged-particle jet spectra in event-shape engineered Pb-Pb collisions at 5.02 TeV with ALICE

The path-length dependence of jet quenching can help to constrain different jet quenching mechanisms in heavy-ion collisions. However, measuring an explicit value for this dependence has proven challenging. Traditional approaches, which consider anisotropic jet suppression arising from geometric asymmetries, have successfully measured a non-zero azimuthal dependence of jet modification with respect to the event-plane angle of the collision. While such signals improve our qualitative understanding of this topic, extraction of an explicit dependence from these results is limited by fluctuations in the initial state and jet-medium interactions. A new approach to characterize the geometry of the collision is to use event-shape engineering, a technique that classifies events within a centrality class according to their elliptical anisotropies. By doing so, we gain an improved knowledge of the initial state medium, consequently enabling better constraints on the average path length traversed by the jet. In this talk, new results of jet spectra from event-shape-engineered collisions at ALICE will be presented along with theoretical studies to contextualize the measurement.

Sprecher: Caitlin Beattie (Yale University)

Beattie_HardProbes2023.pdf

10:40 → 11:10 Coffee Break

11:10 → 12:50 Plenary Session V

Sitzungsleiter: Roberta Arnaldi

11:10 Quarkonia: Theory

Sprecher: Miguel Ángel Escobedo Espinosa (Universitat de Barcelona)

hp2023_escobedo.pdf

11:35 Quarkonia: Experiment

Sprecher: Krista Smith (Los Alamos National Laboratory)

Hard_Probes_2023_Quarkonia.pdf

12:00 Nuclear PDFs: new results from global fits

Sprecher: Tomas Jezo (WWU ITP)

TJezo.pdf

12:25 Saturation physics at e-p and e-A colliders

Sprecher: Paul Caucal (SUBATECH)

HP2023-saturation.pdf

12:50 → 14:00 Lunch Break

14:00 → 16:05 Plenary Session VI

Sitzungsleiter: Magdalena Djordjevic

14:00 UPCs as probes of partonic structure –exclusive and inclusive processes

Sprecher: Vadim Guzey (University of Jyvaskyla)

guzey_hp2023_final.pdf

14:25 Hadronization mechanism (via heavy-flavor hadrons): Experiment

Sprecher: Andrea Rossi (INFN Padova)

2023MarchHardProbes_Rossi.pdf

14:45 Hadronization mechanism (via heavy-flavor hadrons): Theory

Sprecher: Andrea Beraudo

beraudo-HP.pdf

15:05 Panel discussion: Heavy-flavor production and propagation in QGP - recent achievements and challenges for the next decade

Sprecher: Marta Verweij (Utrecht), Dr. Ralf Rapp (Cyclotron Institute and Department of Physics and Astronomy, Texas A&M University), Urs Achim Wiedemann (CERN Theoretical Physics Department)

HP23-HFpanel.pdf

16:05 → 16:30 Coffee Break

16:30 → 18:15 Plenary Session VII

Sitzungsleiter: Johanna Stachel

16:30 Future Facilities: sPHENIX and STAR

Sprecher: Megan Connors (Georgia State University)

HP2023_RHIC_connorsv3.pdf

16:55 Future Facilities: Heavy-ion physics at the LHC beyond Run 4

Sprecher: David Dobrigkeit Chinellato (UNICAMP/CERN)

DDChinellato-HP2023-06.pdf

17:20 Future Facilities: Electron Ion Collider

Sprecher: Friederike Bock

HP2023-EPIC.pdf

17:45 Future Facilities: SPS

Sprecher: Enrico Scomparin (INFN Torino (Italy))

HP2023_Enrico_v2.pdf

18:00 Future Facilities: CBM

Sprecher: Christian Pauly (Bergische Univgersität Wuppertal)

talk_CP_HardProbes23_final.pdf

19:30 → 22:00 Conference Dinner

Freitag, 31. März

09:00 → 09:30 Plenary Session VIII: Flash talks

Sitzungsleiter: Raphaelle Bailhache

09:00 Disentangle effects from the initial stage and the evolution stage in heavy ion collisions using EPOS and PHSD

Ultrarelativistic heavy-ion collisions at RHIC and the LHC provide a hot and ultra-dense form of matter composed of deconfined quarks and gluons, named QGP. Different models like EPOS and PHSD allow to study the space-time evolution of such heavy-ion collisions. Their dynamics is complicated; hence, various stages should be considered. The first is the primary scattering which defines to a large extent the matter distribution in the phase-space. The second stage concerns the evolution of the partonic system until the system is sufficiently dilute to hadronize. The EPOSi+PHSDe approach is introduced in this thesis, in which the EPOS model is used to determine the initial distribution of matter (partons/hadrons). This part is referred to as EPOSi. Then PHSD is employed to simulate the evolution of the matter in a non-equilibrium transport approach, referred to as PHSDe. The coupling of the two approaches is non-trivial and not straight-forward. Comparing the three models, EPOS, EPOSi+PHSDe, and PHSD, interesting results find concerning their respective space-time evolutions. The results demonstrate considerably different behavior in terms of radial expansion, especially asymmetric expansion, indicating that these three models will provide different results concerning key observables ( pT/mT spectra, y/ƞ distribution, v2/3/4) for Au-Au collisions at 200 GeV/A.

Sprecher: Mahbobeh Jafarpour

flash_talk_poster.pdf

09:06 Evolution of initial state fluctuations in the hotspot model

The hotspot model has proven to be an efficient tool to study coherent and incoherent diffraction HERA data by modelling the initial state fluctuations of the gluon density of the proton. The hotspot model in its original form is a non-perturbative model applicable for low momentum transfer and underestimates the incoherent cross section in orders of magnitude when extended for large momentum transfer studies for J/ψ photo-production at HERA. We present here a model of hotspot splittings based on the resolution for the evolution of initial state fluctuations in the hotspot model inspired by the DGLAP parton shower approach This is reliable as both the Bjorken limit and the incoherent diffraction at large momentum transfer probes the gluon wave function at smaller length scales as we increase the resolution. In addition to the geometrical fluctuations, we have additional sources of fluctuations in our model namely the hotspot width, number, and normalisation fluctuations which leads to a good agreement of our model’s prediction with data. In the framework developed, we obtain a good description of both the normalization and shape of coherent and incoherent differential cross sections (t-spectrum) simultaneously.

Sprecher: Arjun Kumar

kumar_HP23.pdf

09:12 Dilepton anisotropy at low beam energies in a transport approach

We present calculations of dielectron anisotropic flow in heavy-ion collisions at HADES beam energies from a hadronic transport approach. The collectivity of the electromagnetic radiation produced during the evolution of these collisions has recently been dubbed as a barometer, serving as a probe for the flow velocity of the underlying hadronic matter. In particular, we study the elliptic flow coefficient $v_2$ of dileptons in different collisions systems, and its relation to the flow of hadrons.

Sprecher: Renan Hirayama

HEMP23_HirayamaRenan.pdf

09:18 Measurement of $\omega$ meson production in pp and p--Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02~$TeV with ALICE

The ALICE experiment at the LHC investigates the properties of the hot and dense nuclear matter created in heavy-ion collisions. By comparing the particle production in pp and p--Pb collisions, possible nuclear initial state effects can be isolated. Measurements of the $\omega$ meson $p_\text{T}$-spectra in pp and p--Pb collisions not only allow for a determination of the nuclear modification factor $R_\text{pA}$, but also provide insights into the fragmentation process and serve as vital input for direct photon cocktail simulations.

The $\omega$ mesons can be reconstructed in ALICE via their primary decay channel into three pions ($\omega\rightarrow\pi^+\pi^-\pi^0$). While the two charged pions are being directly identified by the tracking detectors, i.e. the Time Projection Chamber and the Inner Tracking System, the $\pi^0$ is reconstructed from its two decay photons. These photons can either be detected in the calorimeters or via tracks in case they convert to an electron-positron pair in the detector material.

In this poster, the measurement of the $\omega$ meson production in pp and p--Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02~$TeV will be presented. This includes the signal extraction and various corrections of the $\omega$ meson yields, as well as comparisons to theory calculations.

Sprecher: Nicolas Strangmann

Omega_FlashTalk_HP_Strangmann.pdf

09:24 First performance results from upgraded LHCb and SMOG II

The LHCb experiment has recently undergone a series of major upgrades: the entire tracking system has been replaced with higher-granularity sensors, the readout electronics have been upgraded, and all hardware triggers have been replaced with a new state-of-the-art streaming readout system. In addition, the gaseous target SMOG system has been upgraded with a dedicated storage cell to greatly increase the rate of fixed target collisions at LHCb. This talk will include the first performance results from the new LHCb tracking system, the streaming readout system, and SMOG II, with a focus on how these upgrades directly impact the LHCb heavy ion physics program. Further upgrades planned for LHC Run 4 and 5 will also be discussed.

Sprecher: Chiara Lucarelli

HP23_flashtalk.pdf

09:30 → 10:45 Plenary Session IX

Sitzungsleiter: Julia Velkovska

09:30 Lattice and EFT for hard probes

Sprecher: Rasmus Larsen

Rasmus_Larsen_Hard_Probes_2023.pdf

09:55 Jet quenching with machine learning

Sprecher: YILUN DU

HP23_Yilun_Jet_ML.pdf

10:20 Hard probes at intermediate energies (including fixed-target programs)

Sprecher: Rongrong Ma (BNL)

RMa_HP_2023_update.pdf

10:45 → 11:15 Coffee Break

11:15 → 13:00 Plenary Session X

Vorsitzende der Sitzung: Anton Andronic, Christian Klein-Boesing, Ralf Averbeck, Silvia Masciocchi (GSI - Helmholtzzentrum fur Schwerionenforschung GmbH (DE))

11:15 Highlights, open questions and perspectives: Heavy flavors and quarkonia

Sprecher: Andrea Dubla (GSI-HELMHOLTZZENTRUM FÜR SCHWERIONENFORSCHUNG GMBH)

ADubla_HP2023.pdf

11:40 Highlights, open questions and perspectives: nPDFs and Electroweak Probes

Sprecher: Jamal Jalilian-Marian (Baruch College, CUNY)

hp2023.pdf

12:05 Highlights, open questions and perspectives: Jets and high pT

Sprecher: Laura Havener (Yale University)

JetandHighpTSummary_HardProbes2023_Havener.pdf

12:30 Next Hard Probes edition in Japan

Sprecher: Tatsuya Chujo

HP2024_Nagasaki_presented_at_Ashaffenburg_final.pdf

12:45 Goodbye from the local organizing committee

Sprecher: Chairs