13th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions

21 Jun 2026, 07:00 → 26 Jun 2026, 13:10 America/Chicago

Vanderbilt University

Jean-Francois Paquet (Vanderbilt University), Julia Velkovska (Vanderbilt University (US)), Victoria Greene (Vanderbilt University (US)), Yi Chen (Vanderbilt University (US))

The 13th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions (Hard Probes 2026, HP2026) will take place in Nashville, Tennessee on picturesque campus of Vanderbilt University in the US from 22-26 June 2026.

The student lectures will take place on Sunday, June 21 at Vanderbilt University campus in Nashville. 

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:

• Jet modification and medium response
•  
  High-momentum hadrons and correlations
•  
  Heavy quarks and quarkonia
•  
  Electromagnetic and electroweak probes
•  
  Nuclear PDFs, saturation, and early-time dynamics
•  
  Future experimental facilities and new techniques
•  
  ML/AI and quantum computing in high-energy nuclear physics

Sunday 21 June

08:30 → 09:00 Registration

09:00 → 10:40 Student day: Session - I

Convener: Prof. Rithya Kunnawalkam Elayavalli (Vanderbilt University)

09:00 The life and Adventures of RHIC [30+15 min]

Speakers: Olga Evdokimov (University of Illinois Chicago (US)), Olga Evdokimov (University of Illinois at Chicago (US))

2026_HP_RHICadventures_OE.pdf

09:45 How do we do jet measurements from detector output to measurements? [20 min]

Speaker: Jelena Mijuskovic (University of Montenegro (ME))

HP20206_JetsExperiment_JM.pdf

10:05 A short primer on how jets lose energy [20 mins]

Speakers: Chathuranga Sirimanna, Chathuranga Sirimanna (Duke University)

Jet_Energy_Loss_HP2026_StudentDay.pdf

10:25 Discussion Session

10:40 → 11:05 Coffee Break

11:05 → 12:00 Student day: Session - II

Convener: Prof. Rithya Kunnawalkam Elayavalli (Vanderbilt University)

11:05 How do we measure HF quarks and what have we learned so far? [20 mins]

Speaker: Deepa Thomas (University of Texas at Austin (US))

Student Day Talk HF Expt-June 21.pdf

11:25 How do HF quarks and bound states evolve in a hot dense medium?

Speaker: Mayank Singh (Vanderbilt University)

HP2026_student_day_HF_theory.pdf

11:45 Discussion Session

12:00 → 13:30 Lunch

13:30 → 14:25 Student day: Session - III

Convener: Prof. Rithya Kunnawalkam Elayavalli (Vanderbilt University)

13:30 EW probes and why they are useful to us Exp? [20 mins]

Speaker: Roli Esha (Stony Brook University)

ewprobes_hp2026_esha.pdf

13:50 EW probes and why they are useful to us Th? [20 mins]

Speaker: Chun Shen (Wayne State University)

EMProbes_Th_SHEN.pdf

14:10 Discussion Session

14:25 → 14:55 Coffee Break

14:55 → 17:00 Student day: Session - IV

Convener: Prof. Rithya Kunnawalkam Elayavalli (Vanderbilt University)

14:55 What are some early stage heavy ion physics measurements Exp? [20 mins]

Speakers: Austin Alan Baty (University of Illinois Chicago), Austin Baty (University of Illinois Chicago)

Baty_InitialStages_HardProbes2026_v1.pdf

15:15 Why is the early stage physics important th? [20 mins]

Speakers: Sangyong Jeon, Sangyong Jeon

talk_HP2026_Init_lecture.pdf

15:35 Discussion Session

15:50 Discussion Session with all lecturers

Monday 22 June

08:00 → 08:30 Registration

08:30 → 10:15 Plenaries: Opening plenaries

Convener: Julia Velkovska (Vanderbilt University (US))

08:30 Welcome remarks

HP2026_welcome-plenary.pdf

08:50 Hard Probes of QGP in the past decades

Speaker: Dr Xin-Nian Wang (Lawrence Berkeley National Lab. (US))

HP20260-animated-xnwang.pptx

HP2026-xnwang.pdf

09:20 Emerging Topics for Hard Probes

Speaker: Carlota Andres (CPHT, Ecole polytechnique)

andresc_HP2026.pdf

09:50 sPHENIX Overview

Speaker: Jaebeom Park

sPHENIX_Overview.pdf

10:15 → 10:45 Coffee break (+late registration)

10:45 → 12:20 Plenaries: Experiment overviews

Convener: Victoria Greene (Vanderbilt University (US))

10:45 ALICE Overview

Speaker: Antonio Palasciano (Politecnico & INFN, Bari (IT))

HP2026-ALICE-Palasciano.pdf

11:15 CMS Overview

Speaker: Dr Soohwan Lee (Korea University (KR))

HardProbes2026_v6.pdf

11:40 ATLAS Overview

Speaker: Riccardo Longo (University and INFN Torino (Italy))

ATLAS_Highlights_Longo_HP2026_v1.2HQ.pdf

ATLAS_Speakers_at_HP26_latest.pdf

HP2026_ATLAS_Highlights_Longo_LightVersion.pdf

12:05 PHENIX Overview

Speaker: Takao Sakaguchi

PHENIX_highlight_HP2026_final.pdf

12:20 → 14:30 Lunch break

14:30 → 15:30 Plenaries: Experiment overviews

Convener: John Lajoie (Oak Ridge National Laboratory)

14:30 LHCb Overview

Speaker: Óscar Boente García (CERN)

lhcbOverview_HP2026_oboenteg_v4.pdf

14:50 STAR Overview

Speaker: Barbara Trzeciak (Czech Technical University in Prague)

STARHighlights_BTrzeciak_HP26_final.pdf

15:15 HADES Overview

Speaker: Sukyung Kim (HADES)

HADES_overview_HP2026_vf (1).pdf

15:30 → 16:00 Coffee break

16:00 → 17:40 Plenaries: Heavy Flavor and Quarkonia

Conveners: Prof. Steffen A. Bass (Duke University), Steffen Bass (Duke University)

16:00 Quarkonia: experiment

Speakers: Cesar Luiz Da Silva (Los Alamos National Laboratory (US)), Qian Yang (Shandong University (CN))

HP_v5.pdf

HP_v5.pptx

16:25 Quarkonium and heavy-flavor transport

Speaker: Xiaojun Yao (University of Washington)

XY hard probes 2026.pdf

16:50 Open heavy flavor: experiment

Speaker: Cameron Dean (Massachusetts Inst. of Technology (US))

HF_experiment_C_Dean_20260622.pdf

17:15 Open heavy flavor: theory

Speaker: Ralf Rapp

HP26.pdf

HP26-rapp.pptx

18:30 → 20:00 Reception

Tuesday 23 June

08:30 → 09:50 Parallels: EEC

Convener: Yen-Jie Lee (Massachusetts Inst. of Technology (US))

08:30 Searching for quark-gluon plasma droplets with heavy quark energy correlators

Heavy-flavor jets and their substructure provide a unique window into the role of quark mass on QCD radiation and its modification in hot and dense QCD matter. In this work, we investigate heavy-quark energy-energy correlators (EEC) that are explicitly sensitive to mass effects, focusing on angular correlations, energy flow, and the dead-cone effect. We demonstrate how the finite mass of charm and bottom quarks modifies the intra-jet radiation pattern, leading to characteristic suppressions at small angles and measurable deviations from massless jet expectations. Using effective field theory analysis, we extend the calculation of these observables to heavy-ion collisions, to show that medium-induced radiation and collisional effects compete with vacuum mass suppression, resulting in a nontrivial modification of jet substructure. In particular, we identify regimes where the jet substructure is dominated by the heavy quark mass, leading to qualitatively and quantitatively different behavior of the EEC in nuclear matter, and obtain new analytic results for the energy loss of heavy quark jets. We present results for charm and bottom jet energy-energy correlators modification in heavy ion collisions and discuss their role as diagnostics of quark-gluon plasma formation in small collision systems, complementary to other heavy flavor observables.

Speaker: Dr Ivan Vitev

HP2026_Vitev_New.pdf

08:50 Flavor hierarchy of particle correlation in jets

Heavy flavor jets provide ideal tools to probe the mass effect on jet substructure in both vacuum and quark-gluon plasma (QGP).
Energy-energy correlator (EEC) is an excellent jet substructure observable owning to its strong sensitivity to jet physics at different scales.
We perform a complete realistic simulation on medium modification of heavy and light flavor jet EEC in heavy-ion collisions.
A clear flavor hierarchy is observed for jet EEC in both vacuum and QGP due to the mass effect.
The medium modification of inclusive jet EEC at different angular scales exhibits very rich structure: suppression at intermediate angles, and enhancement at small and large angles, which can be well explained by the interplay of mass effect, energy loss, medium-induced radiation and medium response.
These unique features of jet EEC are shown to probe the physics of jet-medium interaction at different scales.
We further study genuine particle correlation inside jets by using the ratio between the Full EEC and the trivial EEC constructed from two individual energy flows, and find that the near-side behavior of this ratio holds the same in pp and AA collision. Capitalizing on this feature, We quantitatively extract the reduced jet pT for the first time without the reliance of N_{\mathrm{coll}}. This method can also be directly applied to high-multiplicity p-p/p-Pb collisions.

Reference:
[1] Wen-Jing Xing, Shanshan Cao, Guang-You Qin, Xin-Nian Wang, Phys.Rev.Lett. 134 (2025) 5, 052301
[2] Wenbin Zhao, Volker Koch, Feng Yuan, arXiv:2507.18790v1

Speaker: Prof. Guang-You Qin (Central China Normal University)

hp2026_qin_v4.pdf

09:10 Probing fragmentation and hadronization with jets tagged with charm baryons and mesons with ALICE in pp collisions

Jet substructure provides stringent tests of Quantum Chromodynamics (QCD) and offers experimental access to hadronization mechanisms, which remain theoretically challenging. QCD predicts that jet radiation patterns depend on both the mass and the color charge of the initiating parton. In particular, parton showers are sensitive to the different Casimir color factors of quarks and gluons, as well as to the mass of partons through the dead-cone effect. Extending jet substructure studies by comparing baryon- and meson-tagged jets provides insight into hadronization mechanisms and challenges the universality of hadronization across different collision systems.

In this talk, we present three complementary measurements of charm-tagged jets using reconstructed $\mathrm{D}^{0}$ mesons and ${\Lambda_\mathrm{c}^{+}}$ baryons as tags. First, we present measurements of the Energy–Energy Correlator in $\mathrm{D}^{0}$-tagged jets, which resolves the angular structure of the energy flow of QCD radiation and enables a separation of perturbative and non-perturbative contributions in charm parton showers. Second, we measure differences between three jet axis definitions with varying sensitivity to wide-angle soft radiation, providing systematic probes of the radiation pattern of charm quarks. Finally, we extend the measurement of axis difference to charm jets with ${\Lambda_\mathrm{c}^{+}}$ baryons to directly probe modifications to baryonization in hadronic collisions.

Speaker: Christian Reckziegel

FragmentationHadronization_HardProbes.pdf

09:30 Probing cold nuclear matter effects with energy correlators inside jets

We study energy correlators inside jets produced in electron–nucleus deep inelastic scattering events, to probe cold nuclear matter effects. We first investigate the one-point energy correlator (OPEC) inside jets and provide predictions in kinematic regions relevant for the future Electron–Ion Collider. We find that the OPEC exhibits characteristic transition behavior as a function of the angle between the particles and the jet axis. The nuclear modification factor increases with increasing angle, driven by transverse-momentum broadening induced by multiple scattering in the nuclear medium.

We also study the two-point energy correlator (EEC). Employing the high-twist formalism to describe medium-induced parton energy loss, we derive an analytic expression for the nuclear modification of the EEC as a function of the opening angle between the two particles. The modification is found to be strongest at large angles within the jet cone. We further obtain explicit results for the dependence of the EEC modification on the jet energy, the scattering strength of cold nuclear matter, and the path length traversed by the jet in the medium.

References:
1.arXiv:2512.16847
2.Phys.Rev.Lett. 135 (2025) 11, 112302

HP2026_EC_Fu_Mueller_final.pdf

08:30 → 09:50 Parallels: Future

Conveners: Rosi Jan Reed (Lehigh University), Rosi Reed (Lehigh University)

08:30 Prospects for heavy-ion data-taking with the LHCb Upgrade II

Owing to its forward acceptance, complementary to the other LHC experiments, and to its excellent tracking and particle identification, LHCb has conducted a unique heavy-ion physics program since Run 2 of the LHC. By exploiting the injection of gases in the LHC accelerator beam-pipe, LHCb has been simultaneously acquiring data in fixed-target mode. The combination of the two configurations allows for new insights into the physics of high-energy nuclear collisions and unique constraints on theoretical models. Upgrade II of the LHCb detector will begin operations in Run 5, opening even more possibilities due to increased detector granularity, timing capabilities, and instrumentation. In this contribution, an overview, incuding predictions, of the heavy-ion opportunities with LHCb Upgrade II will be presented and discussed.

Speaker: Nicolas Schmidt (Los Alamos National Laboratory (US))

HP26_LHCbUpgradeTalk.pdf

08:50 Dimuon and Charm Experiment at CERN SPS

The NA60+/DiCE experiment is a proposed fixed-target apparatus at the CERN SPS. NA60+/DiCE (Dilepton and Charm Experiment) is dedicated to measuring muon pairs and hadron production over a center-of-mass energy range from 6 to 17 GeV in a variety of collision systems, from Pb+Pb to proton-nucleus interactions. The physics program of the experiment covers the study of rare electromagnetic probes of the Quark-Gluon Plasma, including thermal dilepton radiation from the hot, dense medium, signatures of chiral symmetry restoration, and strangeness and charm production.
The detector combines a high-resolution vertex spectrometer based on large-area silicon MAPS technology with a large-acceptance muon spectrometer employing gaseous tracking detectors. The apparatus is designed to operate with high-intensity ion and proton beams at the SPS, providing access to rare observables that have not been studied at these energies.
The set-up is foreseen to be installed in the SPS H8 experimental area and to start operation after the LHC Long Shutdown 3. In this contribution, we present an overview of the NA60+/DiCE project, with an emphasis on recent detector R&D developments, and studies of the expected physics performance outlined in the Experimental Proposal.

Speaker: Alexander Milov (Weizmann Institute of Science (IL))

DiCE_hp2026_06_23_sasha.pdf

09:10 ALICE Forward Calorimeter upgrade (FoCal): physics program and expected performance

The FoCal is a high-granularity forward calorimeter to be installed as an ALICE upgrade during the LHC Long Shutdown 3 and take data in Run 4. It will cover a pseudorapidity interval of $3.2 < \eta < 5.8$, allowing to explore QCD at unprecedented low Bjorken-$x$ of down to $\approx 10^{-6}$ -- a regime where non-linear QCD dynamics are expected to be sizable.
The FoCal consists of a compact silicon-tungsten sampling electromagnetic calorimeter with pad and pixel readout to achieve high spatial resolution for discriminating between isolated photons and decay photon pairs. Its hadronic component is constructed from copper capillary tubes with scintillator fibers.
The detector design allows measuring a multitude of probes, including direct photons, jets, as well as photo-production of vector mesons in ultra-peripheral collisions and angular correlations of different probes.
After the recent completed of the Technical Design Report (https://cds.cern.ch/record/2696471), the FoCal project is entering the production phase in view of installation in 2028. We will give an overview of the FoCal physics programme, of the detector design and of its expected performance using results from recent test beams of small-scale prototypes.

Speaker: Prof. Ian Gardner Bearden (University of Copenhagen (DK))

FoCal_HardProbes.pdf

09:30 ALICE 3: a next-generation heavy-ion detector for LHC Run 5

ALICE is preparing two upgrades that will be installed during LHC LS3 (2026-29): ITS3 and FoCal. A further upgrade of the full detector system, called ALICE 3, is in preparation for LHC Run 5. The detector consists of a pixel-based tracking system with a large pseudorapidity acceptance, complemented by multiple systems for particle identification, including silicon time-of-flight layers, a ring-imaging Cherenkov detector, a muon identification system, and forward detectors for event characterisation. The ITS3 upgrade is based on newly developed wafer-scale monolithic active pixel sensors, which are bent into truly cylindrical layers and held in place by light mechanics made from carbon foam, provinding a factor two improvement in pointing resolution over the full $p_T$ range. Results from the ongoing development and construction will be presented, with emphasis on the development of the new large-area monolithic sensors. ALICE 3 will further improve on these upgrades by using a full silicon-pixel based tracker, with a retractable vertex detector to reach a pointing resolution of better than 10 micron for $p_T >200$ MeV/c. ALICE 3 will not only enable novel studies of the quark-gluon plasma but also open up important physics opportunities in other areas of QCD and beyond. The presentation will cover the detector concept, the physics performance, and the status of detector R&D.

Speaker: Marco Van Leeuwen (Nikhef National institute for subatomic physics (NL))

ALICE3_MvL_HP2026.pdf

08:30 → 09:50 Parallels: Substructure

Convener: Yasuki Tachibana (Akita International University)

08:30 Jet substructure measurements at LHCb

Jet substructure measurements at the LHC produce precision tests of jet formation and fragmentation in vacuum as well as at the high temperatures and densities formed in heavy-ion collisions. Jets containing a heavy-flavor hadron drive these QCD measurements into a regime where parton mass and colour factors are critical, pushing the limits of theoretical calculations both in-vacuum and in-medium. Mapping out individual emissions in the Lund jet plane for heavy-flavour jets and comparing to light-quark-enriched jets tagged by a Z boson reveals significant mass-dependence to jet fragmentation, offering a decisive channel to decipher in-medium modification to jet fragmentation across different kinematics. At the same time, measuring heavy-flavour jet mass with a theoretically-safe flavour tagging algorithm for the first time tests perturbative QCD at unprecedented theoretical precision and probes the gluon splitting contribution to heavy-flavour production, a yet-unobserved probe of how the medium resolves quark entanglement. The LHCb collaboration presents recent jet substructure results at forward rapidity in pp collisions at centre-of-mass energy √s = 13 TeV. These measurements are compared to theoretical predictions, providing new insight on QCD fragmentation at forward rapidity and at low and moderate values of jet transverse momentum. These results provide a baseline for future measurements of jet quenching in PbPb collisions.

Speaker: Ezra Lesser (Los Alamos National Laboratory)

EzraLesser_HP2026.pdf

08:50 Mapping jet substructure with the Lund Plane and time re-clustering in pp collisions with ALICE

Jets provide well-controlled, multi-scale probes of QCD processes. By resolving jet splittings, differential jet substructure accesses the dynamics governing how colored partons radiate and fragment. The excellent tracking performance and low momentum reach of the ALICE detector enable precise jet splittings measurements, particularly in regimes dominated by non-perturbative effects. This talk presents complementary representations of jet substructure that emphasize both the kinematic and temporal structure of parton splittings.

The primary jet Lund Plane provides a 2D representation of jet splittings in relative transverse momentum and opening angle, enabling a systematic exploration of QCD radiation within jets. Using high statistics Run 3 data at $\sqrt{s}$ = 5.36 TeV, we perform a 3D Lund Plane study in pp collisions, adding the $p_\mathrm{T}^{\mathrm{jet}}$ in addition to the variables discussed above, to probe the evolution of non-perturbative QCD effects. In addition to conventional angular-ordered C/A re-clustering, we investigate an alternative time-based ($\tau$) re-clustering scheme.
The differences exhibited by groomed jet substructure observables when calculated using angular- and time-ordered re-clustering in pp collisions, highlight sensitivity to the underlying ordering variable and are important for extending MC generators to higher orders.

These results establish a baseline in pp collisions and motivate future applications in Pb-Pb collisions at 5.36 TeV, where the Lund Plane can be used to map jet-medium interactions. Since angular ordering may not be respected by medium-induced emissions, $\tau$ re-clustering offers a promising tool to both study medium-induced modifications of jet structure and to separate the magnitude of quenching effects in early and late splittings.

Speaker: Zoltan Varga (Yale U.)

LundPlane_Varga_HP2026.pdf

09:10 Probing jet modification and substructure with gamma-hadron correlations and reconstructed jets in PHENIX

Energy loss by hard partons traversing the quark--gluon plasma causes the particle yields and internal structure of jets to be modified. These modifications can be measured using two-particle azimuthal correlations by triggering on high-$p_T$ particles and measuring the associated hadron yield as a function of the relative azimuthal angle which are also sensitive to the medium response to energy loss. Previous PHENIX $\pi^0$--hadron correlation measurements demonstrate the azimuthal distribution of the strong suppression of away-side high-$p_T$ hadrons accompanied by enhanced low-$p_T$ particle production, indicating a significant medium response. As compared to $\pi^0$--hadron measurements that are subject to surface and fragmentation biases, direct-photon--hadron correlations, where the photon is unaffected by the strong interaction, provide an unbiased trigger of the initial hard-scattering kinematics. The per-trigger yield of direct photon-hadron pairs is extracted via statistical subtraction of decay photon contributions from the inclusive photon--hadron sample. These measurements provide quantitative insight into in-medium parton energy loss and redistribution of the lost energy within the quark--gluon plasma. In this talk, the latest result on the direct-photon-hadron correlations using the high-statistics Au+Au dataset collected by PHENIX during the 2014 RHIC run will be presented.

Speaker: Mate Rehman (Georgia State University)

jet_quenching_direct_photon_hadron_Hard_Probes.pdf

09:30 sPHENIX measurements of jet production and properties in p+p collisions

The sPHENIX experiment at the Relativistic Heavy Ion Collider is designed to study the properties of the Quark-Gluon Plasma (QGP) using high-energy jets as calibrated hard probes. With large-acceptance, high-granularity calorimetry and tracking subsystems, the detector enables precision measurements of jet production and jet substructure observables that are sensitive to the medium-induced modifications of parton showers. During the 2024 RHIC run, sPHENIX collected an integrated luminosity of 107/pb in proton-proton (p+p) collisions at a center-of-mass energy of 200 GeV, utilizing an efficient high-pT jet trigger. This talk reports a measurement of the inclusive jet cross-section in p+p collisions as a function of jet transverse momentum for radius parameters R from 0.2 to 0.6, reaching out to pT = 70-80 GeV. The results are compared with a variety of modern event generators, as well as perturbative QCD calculations. Furthermore, measurements of jet sub-structure observables such as the subjet opening angle, θsj, and the momentum sharing fraction, zsj, and others which are sensitive to the energy distribution within the jet, including the mass over transverse momentum (m/pT) and the radial jet shape, are reported. These measurements in p+p collisions represent an important baseline for future measurements of jet modification in Au+Au and O+O collision data, which will give insight into the color and medium coherence scales in the QGP.

Speaker: Hanpu Jiang (Columbia University)

HP2026_Hanpu.pdf

08:30 → 09:50 Parallels: Small and Intermediate system

Convener: Weiyao Ke (Central China Normal University)

08:30 Investigating the nature of cosmic rays through charged hadron production in p+O collisions at ATLAS

By colliding protons with oxygen ions, the LHC enables studies of fundamental properties of matter at extraordinary range of energy scales of ~10 TeV. The recent p+O collisions at the LHC reproduce key features of PeV cosmic-ray interactions with the Earth’s atmosphere. Interpreting data from ground-based cosmic-ray detectors relies on detailed simulations of hadronic interactions at TeV-scale center-of-mass energies. These simulations are based on phenomenological models that require tuning to collider data, particularly in the forward and high-energy regimes. This talk presents the first measurement of prompt charged-particle production in proton–oxygen collisions at $\sqrt{s_{NN}}$=9.62  TeV, delivering key constraints for tuning the hadronic models and aiding the development of cosmic-ray air showers generators.

Speaker: Patrik Novotny (Weizmann Institute of Science (IL))

HP_pO_MinBias_fin3.pdf

08:50 Jet-like dihadron correlations in pO, OO, and Ne–Ne collisions with ALICE

Heavy-ion collisions are primarily studied to investigate the properties of hot and dense primordial nuclear matter, known as the quark–gluon plasma (QGP). However, recent observations of hydrodynamic flow–like behavior in pp and p–Pb collisions at the LHC suggest the possible formation of QGP droplets even in the smallest collision systems. To bridge the multiplicity gap between small and large systems and to examine the applicability of hydrodynamic descriptions, light-ion collisions have been studied for the first time at the LHC.

This contribution presents dihadron correlation measurements in pO, OO, and Ne–Ne collisions by ALICE to explore possible medium effects. The width of the near-side jet-fragmentation correlation peak is studied as a function of collision centrality and midrapidity charged-particle multiplicity. At low transverse momentum ($p_{\rm T}$), a broadening of the near-side peak is observed in OO and Ne–Ne collisions relative to pp and pO collisions, approaching what is observed in Pb–Pb collisions for central events. At higher $p_{\rm T}$, a modest narrowing of the near-side peak is observed with increasing multiplicity. Further, the per-trigger normalized relative yields of near-side and away-side correlations, $I_{\rm AA}$, are measured in OO and Ne–Ne collisions for the first time.

The observed modification of the near-side correlation peak and the relative yields with system size may reflect the interplay between medium-induced effects and other contributions in these collision systems. The results are compared with predictions from several model calculations, including PYTHIA, AMPT, and JETSCAPE.

Speaker: Joonsuk Bae (Sungkyunkwan University (KR))

light_ion_Dihadron_Corr_HardProbes_2026_v4.pdf

09:10 Measurement of charged particle nuclear modification factor in OO and study of nPDF effects using pO collisions

High-$p_{T}$ charged-particle suppression in heavy-ion collisions like PbPb, quantified by the nuclear modification factor $R_{AA}$, is a key signature of parton energy loss in quark-gluon plasma. However, it remains inconclusive in smaller systems like pPb. The first oxygen-oxygen run at the LHC provides a unique opportunity to study this suppression dependence on system size. We present the first measurement of charged-particle differential cross sections and $R_{AA}$ in OO collisions at $\sqrt{s_{NN}} = 5.36~\mathrm{TeV}$ using CMS data. The results are compared with models incorporating parton energy loss. Before attributing the observed suppression to energy loss, it is crucial to consider nuclear parton distribution function (nPDF) effects which can substantially contribute to suppression. Collision systems such as proton-oxygen provide a unique opportunity to test nPDF effects and also provide nPDF constraints for oxygen nuclei. We also present a measurement of charged-particle production in pO collisions at $\sqrt{s_{NN}} = 9.62~\mathrm{TeV}$ using CMS data. To isolate the initial state effects, a ratio of pO spectra is taken to proton–proton (pp) reference at $\sqrt{s_{NN}} = 5.36~\mathrm{TeV}$. The ratio is compared to the state of the art perturbative QCD calculations. The level of agreement between data and theoretical calculations will provide unique oxygen nPDF constraints and establish a quantitative baseline for interpreting particle suppression observed in oxygen–oxygen collisions.

Speaker: Vipul Pant (University of Illinois Chicago (US))

HardProbes2026_talk.pdf

09:30 Neutral pion nuclear modification factor in OO and pO collisions

Energy loss of high-momentum partons is one of the key signatures of the quark-gluon plasma formed in heavy-ion collisions.
Through measurements of the nuclear modification factor $R_{\rm AA}$, where a strong suppression of high $p_{\text{T}}$ particle yields is observed, parton energy loss has been confirmed in Pb--Pb collisions at the LHC.
However, in small collision systems, like pp and p--Pb, energy loss has not yet been confirmed.

In this talk, a measurement of the $R_{\rm AA}$ in OO and pO collisions at $\sqrt{s_{\rm NN}} = 5.36$ TeV and $\sqrt{s_{\rm NN}} = 9.62$ TeV, respectively, is presented. These results are based on the measured particle $p_{\text{T}}$ spectra of $\pi^0$ in OO, pO, and pp collisions using the ALICE Electromagnetic Calorimeter.
The measurement of the $R_{\rm pO}$ allows precise constraints on cold-nuclear matter effects. In combination with the $R_{\rm OO}$, this allows for a separation of cold and hot nuclear matter contributions and enables a quantitative determination of partonic energy loss in OO collisions.
The measurements are compared to theoretical model calculations that include both cold and hot nuclear matter effects.

Speaker: Nicolas Strangmann (Goethe University Frankfurt (DE))

OOEnergyLoss_HP26.pdf

09:50 → 10:20 Coffee break

10:20 → 12:00 Parallels: HF and Quarkonia

Convener: Roberta Arnaldi (Universita e INFN Torino (IT))

10:20 Heavy quark drag coefficient using phonon-heavy quark EFT ($\phi$-EFT)

The description of heavy quarks inside the QGP medium, especially at low momenta, remains challenging from first principles, due to large coupling strength and gluon occupation numbers. An alternative way to formulate a description in terms of perturbative degrees of freedom is the interaction of the heavy quarks with the collective excitations of the medium in form of phonons. This description is derived as an effective field theory (EFT) and therefore allows for a natural occurring power counting of the allowed interactions. This EFT has already been established in our previous work (arXiv:2510.13942), where we have derived the phonon-heavy quark interactions and calculated their thermal scattering cross section.
In this work, we use these results, together with the heavy quark expansion, to calculate the heavy quark drag coefficient $A$. Subsequently, we compare our results with the drag coefficient obtained from AdS/CFT calculations to determine the previously unknown Wilson coefficients for the quark-phonon coupling. Additionally, we determine the same Wilson coefficients by matching the EFT result of the drag force at low momenta with the QCD result at high momenta. Finally, we will compare our results with experimentally determined heavy quark diffusion coefficient.

Speaker: Andreas Kirchner

QHEFT_Andreas_Kirchner.pdf

10:40 Evolution and Equilibration of the Heavy Quark Momentum Distribution in QGP Beyond the Non-Relativistic Limit

The dynamics of heavy quarks in quark-gluon plasma (QGP) formed in heavy ion collisions provide a unique window to characterize its properties. Existing approaches to describe heavy quarks in medium rely either on quasiparticle-based models of QGP, or on assuming that the momentum transfer from the medium follows Gaussian statistics. However, in the prototypical strongly coupled gauge theory, $\mathcal{N}=4$ SYM theory, it has been long known there are no momentum-carrying quasiparticles, and furthermore, we have recently shown that the momentum transfer from the medium is far from being Gaussian [1]. Since then, we showed that the asymmetry of said momentum transfer between energy loss and energy gain — which affects all moments of the distribution — is, in fact, theory-independent [2]. The deviations from Gaussianity can be substantial even at moderate Lorentz boost factors $\gamma = E/M \gtrsim 2$.

In this talk, we present a new framework for calculating how the distribution of heavy quark momenta evolves that encodes all of the non-Gaussian features of the momentum transfer from the medium, all of which can be defined rigorously, from first principles, in QCD or in any gauge theory, without relying on any assumptions regarding the strength of the coupling or the speed of the heavy quark. As a demonstrative example, we discuss how heavy quark stopping and equilibration takes place in $\mathcal{N} = 4$ SYM theory highlighting clear quantitative differences between the full theory and the Gaussian truncation, and the role of ''survivor bias'' effects. This paves the way towards extracting information about fundamental properties of QGP that have not previously been accessible in ways that are both empirical and reliable.

[1] 2501.06289
[2] 2504.21139

Speaker: Bruno Scheihing (KITP, University of California, Santa Barbara)

BScheihing-Talk.pdf

11:00 Heavy Quark Quenching in the Hybrid Strong/Weak-Coupling Model

We present the first heavy-flavor extension of the Hybrid strong/weak-coupling model of jet quenching, enabling a unified description of heavy-flavor hadronic observables down to low $p_T$ and heavy-flavor jet observables as reported in 2510.24847. We implement a composite strongly-coupled heavy-quark energy-loss prescription that interpolates between the ultrarelativistic and drag limits calculated in AdS/CFT, coupled to Gaussian momentum broadening, and include charm recombination with medium partons via Local Color Neutralization. Confronting PbPb data, we find that simultaneously describing prompt $D^0$ suppression and flow requires the combined action of strongly-coupled energy loss, diffusion/broadening, and recombination. Upon adding only a single new parameter $\kappa_{\rm HQ}$ governing heavy quark energy loss and momentum diffusion to the Hybrid Model, we obtain a simultaneous description of prompt and non-prompt heavy-flavor observables, including $R_{AA}$, $v_2$, baryon-to-meson ratios, and b-tagged jet suppression over the available range of transverse momentum, and across multiple centrality classes.

Speaker: Jean Du Plessis

HardProbes2026Nashville.pdf

11:20 Probing Charm Hadronisation through Baryon-Meson and Strangeness-Sensitive Flow Measurements at CMS.

The hadronisation of charm quarks within the Quark-Gluon Plasma (QGP) provides a unique laboratory to study non-perturbative QCD dynamics and the collective evolution of the medium. We present new measurements from the CMS experiment utilising lead-lead (PbPb) collision data. We report the first CMS measurement of the elliptic flow ($v_2$) of the prompt $\Lambda_{c}^{+}$ baryon using the high-statistics Run3 data. This measurement offers a direct test of charm quark thermalisation and the participation of charm baryons in the medium's anisotropic expansion. In addition, we present the new measurements of anisotropic flow of prompt $D_{s}^{+}$ mesons utilising CMS Run 2 data, which serve as a sensitive probe of the strangeness-rich QGP environment. Finally, we compare the azimuthal anisotropy of both the $\Lambda_{c}^{+}$ baryon and the $D_{s}^{+}$ meson with that of the non-strange $D^{0}$ meson. Comparing these results to the precision $D^{0}$ baseline allows us to isolate the specific influences of baryon-versus-meson formation and influence of strangeness on charm quark hadronisation, providing crucial constraints for theoretical models.

Speaker: Diwakar Singh Yadav (Indian Institute of Technology Madras (IN))

Hard_Probes_2026.pdf

11:40 An Integrated Framework for Heavy-Flavor Transport in Nuclear Collisions

Heavy quarks are unique probes of the transport properties and hadronization of the quark–gluon plasma formed in ultra-relativistic heavy-ion collisions, but their strong coupling to the evolving medium requires a multi-ingredient approach for reliable descriptions of in-medium interactions.

We present a newly developed framework [1] that combines state-of-the-art ingredients for heavy-flavor transport in hot QCD matter. It couples nonperturbative elastic interactions to relativistic Langevin dynamics with diffusion and medium-induced gluon radiation, embedded in a 2+1D viscous hydrodynamic evolution. Hadronization is evaluated with a four-momentum conserving recombination approach supplemented with fragmentation constrained by proton–proton data, followed by diffusion in the hadronic phase using the Ultra-relativistic-Quantum-Molecular-Dynamics (UrQMD) model.

We report our recent results for charm-hadron nuclear modification factors, elliptic flow, and charm hadro-chemistry ratios, and compare them to Pb–Pb data at $\sqrt{s_{NN}}=$ 5.02 TeV from ALICE and CMS as well as Au–Au data at $\sqrt{s_{NN}}=$ 200 GeV at RHIC. Constraints on heavy-flavor diffusion coefficients in hot QCD matter are discussed.

[1]: T. Krishna, R. Rapp, Y. Fu, S. A. Bass, and W. Ke, Phys. Lett. B 871 (2025) (139999)

Speaker: Tharun Krishna Vodur Satheesh Kumar (Cyclotron Institute, Texas A&M University)

TK_Hard_Probes_26.pdf

10:20 → 12:00 Parallels: Jet

Conveners: Olga Evdokimov (University of Illinois Chicago (US)), Olga Evdokimov (University of Illinois at Chicago (US))

10:20 Probing flavor-dependent jet quenching and dijet correlations in Pb+Pb collisions with ATLAS

Jets produced in ultra-relativistic heavy-ion collisions lose energy while traversing the quark--gluon plasma, leading to suppressed yields and modified properties relative to proton--proton collisions. Measurements of jet suppression and correlations provide complementary insight into the mechanisms of partonic energy loss and the response of the medium.  This talk presents ATLAS measurements of flavor-dependent jet suppression in Pb+Pb collisions, including the nuclear modification factor, RAA, of b-tagged jets, probing the role of heavy-quark mass in jet quenching. Measurements as a function of rapidity, extending to the most forward region accessible with ATLAS, further constrain the kinematic and flavor dependence of energy loss. Complementary information is obtained from dijet measurements, where pairs of high-energy jets probe both the modification of parton showers and the redistribution of lost energy. The azimuthal angular decorrelation between the two leading jets, quantified via Δϕ, is measured as a function of collision centrality and jet kinematics, providing sensitivity to medium-induced radiation and transverse momentum broadening. Together, these measurements provide a comprehensive and differential picture of jet--medium interactions, constraining both the flavor dependence of energy loss and the mechanisms governing medium response in Pb+Pb collisions.

Speaker: Franciszek Pauwels (Charles University (CZ))

Pauwels_HP_26.pdf

Pauwels_HP_26.pdf

10:40 Exploring small-angle emissions in D0-tagged jets in PbPb collisions at 5.02 TeV with CMS

Speaker: Lorenzo Frosina (Sapienza Universita e INFN, Roma I (IT))

DjetsPbPb_HardProbes2026.pdf

11:00 B-hadron identification in b-jets using novel deep learning technique in pp and PbPb collisions in CMS

Advancements in geometric deep learning offer powerful tools to study the internal structure of jets initiated by heavy quarks, particularly in the context of dead-cone effect and jet quenching. The kinematics of b-hadron decays present a challenge for substructure measurements with inclusive b-jets, which are essential for quantum chromodynamics (QCD) studies. We propose an approach using graph-based deep learning that utilises charged decay products of the jets represented as point clouds to simultaneously identify tracks associated with b-hadron decay and perform b-jet tagging. The method is demonstrated in simulated p-p ($\sqrt{s}=5.02 \ TeV$) and Pb-Pb ($\sqrt{s_{NN}}=5.02 \ TeV$) collisions passed through the CMS detector framework in Run 2 conditions. We benchmark our method against traditional boosted decision tree classifiers, showcasing significant performance improvements in b-hadron identification of tracks.

Speaker: Jelena Mijuskovic (University of Montenegro (ME))

HP2026_JMijuskovic.pdf

11:20 Modification of the Substructure of D$^0$-Meson-Tagged Jets in Heavy-Ion Collisions at STAR

The Quark-Gluon Plasma (QGP) produced in heavy-ion collisions can be studied using hard probes, such as D$^0$-meson-tagged jets initiated by charm quarks produced at the initial stage of the collision. The jet structure is modified through interactions with the medium compared to its propagation in vacuum.

The jet structure can be characterized using the generalized angularities $\lambda_{\alpha}^{\kappa}$, which probe the momentum and angular distributions of jet constituents [1]. Moreover, they can distinguish between jets initiated by light quarks, heavy quarks, and gluons. Varying the parameters $\kappa$ and $\alpha$ tunes the sensitivity to the color-charge and mass effects. Measurements of the nuclear modification factor $R_{\text{CP}}$ of D$^0$-meson-tagged jets as a function of generalized angularities in heavy-ion collisions open ways to investigate modifications of heavy-quark-initiated jet substructure.

In this contribution, we report the first measurement of the generalized angularities $\lambda_{\alpha}^{\kappa}$ for D$^0$-meson-tagged jets in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}} = 200$ GeV by the STAR experiment at RHIC, and the corresponding nuclear modification factor $R_{\text{CP}}(\lambda_{\alpha}^{\kappa})$. These results provide new constraints on theoretical models of jet quenching and heavy-flavor energy loss in the QGP.

[1] A.J. Larkoski, J. Thaler and W.J. Waalewijn, Gaining (Mutual) Information about Quark/Gluon Discrimination, JHEP 11 (2014) 129.

Speaker: Ondrej Lomicky (Czech Technical University in Prague)

HP2026LomickyPresFinal.pdf

11:40 Constraining heavy-quark gluon splittings in high-\pt heavy-quark tagged jets

The study of gluon splittings into heavy-quark pairs, g → c c̄ and g → b b̄, in pp collisions is essential for understanding the mechanisms of heavy-flavor production inside jets and for testing perturbative QCD in the quasi-collinear regime. These processes contribute significantly to heavy-flavor yields at high transverse momentum and are a key component of parton-shower evolution, yet they remain among the least directly constrained elements of current theoretical descriptions. In the presence of a hot medium, formed in ultrarelativistic heavy-ion collisions, the rate of high-pT jets containing g → c c̄ and g → b b̄ splittings is predicted to be enhanced as a result of gluon rescatterings with the medium constituents. In this talk, we present CMS measurements that exploit new heavy-quark tagging techniques to select a high-purity sample of heavy-quark jets and maximize sensitivity to gluon-splitting processes. In pp and PbPb collisions, we report the first measurement of the fraction of g → c c̄–tagged jets as a function of jet pT, compare the results to state-of-the-art theoretical calculations, and quantify the constraints these data impose on parton-shower modeling of heavy-quark splittings.

Speaker: Abraham Thomas Holtermann (Massachusetts Inst. of Technology (US))

g2bbbar_vfinal.pdf

10:20 → 12:00 Parallels: nPDF/Saturation/Early

Conveners: Matthias Kaminski, Matthias Kaminski (Max-Planck-Institu für Physik)

10:20 Disentangling Sub-Eikonal Flow Effects: Boosts vs Quantum Effects

It has been of recent interest to the field to consider the novel coupling of jets to the collective flow of the QGP. In this talk, we systematically contrast the implementation of flow effects via direct inclusion at the level of the scattering potential ("jet drift") and via Lorentz boosted isotropic broadening ("global boost", e.g. CoLBT, MARTINI, etc.). First, we identify the precise spatial and quantum interference pieces missing from the boost implementation and discuss the intimate relationship with the details of the spatial integral over the medium. After establishing the theoretical ingredients, we discuss how to consistently implement jet drift in a Monte Carlo event generator. We introduce a modification to the gradient expansion technique introduced in the derivation of jet drift and discuss the interpretation of the results of the original and new gradient expansions. Finally, we quantitatively compare the effect of jet drift and the global boost technique on new observables in several collision systems using an improved version of the purpose-built Anisotropic Partonic Evolution (APE) event-by-event Monte Carlo. We show that jet drift can be used to probe features of the medium that are not treated by the boost implementation.

Speaker: Joseph Bahder (Central China Normal University)

Bahder_Subeikonal_Flow_Boosts_Phases_2026_Vanderbilt_Hard_Probes.pdf

10:40 Jet Drift in Heavy-Ion Collision: Acoplanarity and v2

“Jet drift,” the preferential deflection of energetic particles in the direction of a flowing quark-gluon plasma, is one of a new class of asymmetric measures of jet modification. Arising from sub-eikonal interactions, jet drift goes beyond a trivial boost of frame and is sensitive to tomographic information about the medium. While energy loss alone is primarily sensitive to the path length and temperature of the plasma, jet drift is directly sensitive to the flow profile; drift is also nontrivially correlated with the energy loss, since particles that lose more energy drift more. To disentangle the dependence of jet drift on the size, shape, temperature, and flow of the medium, we explore the effect of drift on two observables – the elliptic flow $v_2$ of hard particles, and the dihadron acoplanarity – for different collision energies and geometries. Specifically, we study PbPb collisions at 5.02 TeV, AuAu collisions at 200 GeV, and UU collisions at 197 GeV using the Anisotropic Parton Evolution (APE) Monte Carlo simulation. We find that the drift enhancement to acoplanarity depends primarily on the event temperature, while the drift enhancement to $v_2$ emerges from both the temperature and geometry (ellipticity). Using event shape engineering techniques, we select on events with comparable temperature or comparable geometries to disentangle the contributions to the drift enhancement of elliptic flow. Isolating the signatures of jet drift through its systematic dependence on geometry, temperature, and flow will help to reveal how drift encodes this additional tomographic information, where its effects may be largest.

Speaker: Mr Hasan Rahman (New Mexico State University)

HP2026_Parallel_Talk_Hasan_Rahman.pdf

11:00 DIS dijet production with finite-energy corrections and its back-to-back limit

The DIS dijet production at next-to-eikonal accuracy computed in a highly boosted gluon background field within the Color Glass Condensate (CGC) framework will be discussed. In particular, the back-to-back limit of the process will be considered.

Various types of finite-energy corrections and their structures as field strength insertions on the CGC Wilson lines will be shown. These particular forms of the corrections provide direct relation with the gluon TMDs defined from the two-point correlators of the field strength.

The interplay between the subeikonal corrections in the CGC and the higher twist corrections in the TMD factorization will be also highlighted.

Speaker: Alina Czajka (National Centre for Nuclear Research)

Nashville_2026_DIS_NEik.pdf

11:20 Electron-Ion Collisions in the JETSCAPE framework

We present the first results from the JETSCAPE multi-stage event generator framework for electron-ion collisions. The use of calibrated modules from the JETSCAPE framework allows common model parameters to remain unchanged between p-A and e-A simulations, thereby introducing novel constraints on these extensive simulations. The e-A event generator within the JETSCAPE framework simulates an incoming virtual photon scattering off a quark, which develops into a parton shower within the extended nucleus described by the 3D-Glauber model [1]. The interacting shower is simulated using the multi-stage, recoil-based formalism of MATTER + LBT, similar to that carried out for A-A and p-A in JETSCAPE [2,3,4]. The distributions of incoming partons are sampled using a Transverse Momentum Dependent Parton Distribution Function (TMDPDF) within each nucleon. Keeping track of the color structure of the shower and recoil partons, as well as the wounded nucleons, allows for the incorporation of extensive string-based hadronization routines inside a nuclear environment. We present preliminary results on the attenuation, dihadron correlation, and transverse broadening of leading hadrons produced in Deep Inelastic Scattering on Neon, Krypton, and Xenon, and compare these with data from the HERMES collaboration.

[1] C. Shen and B. Schenke, Phys. Rev. C 97, 024907 (2018).
[2] A. Majumder, Phys. Rev. C 88, 014909 (2013).
[3] Y. He et al., Phys. Rev. C 91, 054908 (2015).
[4] A. Kumar et al.,(JETSCAPE) Phys. Rev. C 107, 034911 (2023).

Speaker: Eric Kolbusz (Wayne State University)

EricKolbusz-HP2026-Final.pdf

10:20 → 12:00 Parallels: Small and Intermediate system

Convener: Anne Marie Sickles (Univ. Illinois at Urbana Champaign (US))

10:20 Probing jet-hadrochemistry modifications with measurements of identified particles in jets and the underlying event in pp and Pb--Pb collisions with ALICE

Jet substructure measurements in heavy-ion (HI) collisions constrain the microscopic interaction mechanisms between energetic partons and the quark–gluon plasma. Jet-quenching models predict modifications of the jet-hadrochemical composition in heavy-ion collisions due to jet-medium interactions, allowing measurements of identified particles in jets to help discriminate between different proposed jet-medium interaction mechanisms. Furthermore, models with a jet wake, imprinted on the medium by the traversing jet, predict enhanced soft-particle production at large angles from the jet axis. As such, jet-hadrochemistry studies can also probe the thermalisation properties of the QCD medium.

We present the first measurements with ALICE of $\pi$, K, and p ratios within charged-particle-jets and the underlying event as a function of particle transverse momentum in pp and Pb--Pb collisions, providing the first hints of jet-hadrochemistry modifications in HI collisions. We also report a new study using the high-statistics data sample of Run 3, which measures the jet radial dependence of the particle composition in Pb--Pb collisions for the first time. This differential measurement probes the transition from the hard jet core to its soft periphery, yielding key insights into medium response and QCD thermalisation in the jet wake. These measurements leverage the excellent PID capabilities of ALICE over a wide momentum range. We compare the results with theoretical models to probe the relative effects of modified jet fragmentation and medium response.

Speaker: Sierra Cantway (Yale University (US))

HP26_Cantway_ALICE_piKp_jet_pp_PbPb_FINAL.pdf

10:40 Multiplicity-dependent strangeness production in and out-of-jets in pp and OO collisions with ALICE

At the LHC, the ALICE experiment has observed that the yield ratios of strange to non-strange hadrons increase with charged-particle multiplicity at midrapidity, following a smooth evolution across collision systems, spanning over three orders of magnitude in multiplicity and saturating in central Pb–Pb events. Various models have been proposed to explain the origin of strangeness production in small systems, including statistical hadronization with canonical suppression and color rope hadronization including color reconnection. Experimental efforts focus on identifying observables and phase-space regions where these models make distinct predictions in order to disentangle their underlying mechanisms.

In this contribution, we present the first measurement of strange-hadron production inside and outside fully reconstructed jets as a function of event multiplicity in pp and OO collisions at $\sqrt{s_{\rm NN}}$ = 5.36 TeV, recorded by ALICE during Run 3. By separating jet-associated and underlying-event contributions, these results offer new insight into the interplay between hard and soft QCD processes and their role in driving the multiplicity-dependent enhancement of strangeness production.

Speaker: Mr Alberto Caliva (Universita e INFN, Salerno (IT))

Strangeness_in_jets_ALICE.pdf

11:00 Hadron–strangeness correlations as a function of multiplicity in pp and p-Pb collisions with ALICE

Measurements in pp and p-Pb collisions have revealed that small collision systems exhibit several features traditionally attributed to heavy-ion collisions, including the smooth increase of the strange hadron yields with the collision multiplicity (strangeness enhancement). However, the microscopic origin of this phenomenon in small systems remains an open question. In particular, the relative contributions of soft (bulk-like particle production) and hard processes (related to parton fragmentation and jet production) to strangeness enhancement in small collision systems are not yet fully constrained. Angular correlations between a charged hadron and an associated strange hadron provide a differential tool to probe different strangeness production mechanisms and to study the interplay between bulk and hard particle production.

In this contribution, we present the first measurement of two-particle angular correlations involving identified strange hadrons as a function of multiplicity in pp collisions at $\sqrt{s}$ = 5.36 TeV and p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. The results are compared with state-of-the-art model predictions, providing new insights into the interplay between hard and soft QCD processes governing strangeness production in small collision systems.

Speaker: Lucia Anna Tarasovicova (Pavol Jozef Safarik University (SK))

StrangenessCorrelations_HP.pdf

11:20 sPHENIX high-statistics measurements of strangeness production in p+p collisions

The new sPHENIX collider detector experiment features a unique tracking system capable of streaming readout, enabling the collection of very large, unbiased p+p datasets previously not available at RHIC. sPHENIX recorded over 10 pb$^{-1}$ of p+p collisions at 200 GeV in this readout scheme. Using these datasets, new measurements of the transverse-momentum and multiplicity dependence of strange light hadrons can yield key insights about the onset of QGP formation. As the strange quark mass is below the critical temperature, they can be thermally produced inside the QGP. By measuring the relative production of $Λ^0$ baryons to $K^0_S$ mesons in p+p collisions, a key baseline measurement is performed that, when compared to later open heavy flavor measurements in collision systems such as Au+Au and O+O, will enable sPHENIX to make quantitative statements on hadronization mechanisms such as co-mover effects and color reconnection at RHIC energies. Furthermore, such measurements can be used as a data-driven determination of the sPHENIX tracking efficiency map, such as by comparing the production rates of neutral and charged kaons in specific kinematic regions.

Speaker: Hao-Ren Jheng (Massachusetts Inst. of Technology (US))

HP2026-HRJheng.pdf

11:40 Bridging Vacuum and Dense QCD with Jet and Event Shape from the Electron-Positron Alliance

High-energy nuclear collisions reveal the QCD radiation and hadronization in the most complex many-body environment accessible in the laboratory. To interpret these phenomena, it is essential to establish a precise understanding of the corresponding vacuum dynamics. Electron-positron annihilation provides a uniquely clean setting where the initial state is color neutral and free of hadronic structure, allowing final-state QCD evolution to be studied with minimal ambiguity. We present recent new measurements from the Electron-Positron Alliance aimed at building precision vacuum references for jet formation, energy flow, and hadronization. This talk includes measurements of identified-particle production, such as the K/pi ratio, energy-energy correlators, jet, and jet substructure observables. It also includes an investigation of an agentic AI-based method for the event thrust analysis. These observables probe complementary aspects of QCD final states, from inclusive energy redistribution and flavor-dependent hadronization to angular correlations, jet geometry, and the scale dependence of reconstructed jets. Electron-positron data can serve as a bridge between vacuum QCD, event-generator modeling, and measurements in increasingly complex collision systems. Comparisons from e⁺e⁻ to pp, and ultimately to heavy-ion collisions, can help isolate which features arise from universal vacuum showering and hadronization, and which reflect initial-state structure, underlying event activity, or genuine medium-induced modification.

Speaker: Yen-Jie Lee (Massachusetts Inst. of Technology (US))

20260623_EPAJet_yenjie_v10.pdf

12:00 → 14:00 Lunch break

14:00 → 15:20 Parallels: E&M

Convener: Lijuan Ruan

14:00 The impact of phase transitions on dilepton production

We calculate dielectron yields for different equations of state at beam energies relevant for the CBM experiment at FAIR and the STAR Beam energy Scan. The production of dielectrons of intermediate masses ($1\leq m_{ee}/\mathrm{GeV}\leq3$) is increased by the presence of a phase transition, due to the latent heat. In this work, we quantify this enhancement using a hybrid model of hadronic transport+hydrodynamics with a realistic set of dynamic initial conditions [1], where dileptons are radiated directly by hadrons in the off-equilibrium evolution, and via thermal rates in the fluid [2].

[1] Góes-Hirayama et al. (2025) arXiv:2507.19389 [hep-ph]
[2] Góes-Hirayama et al. (2025) arXiv:2510.02862 [nucl-th]

Speaker: Renan Góes-Hirayama (FIAS)

dynamical_IC_hybrid_AuAu_5.2GeV_until_11.5fm.mp4

talk_RenanHirayama.odp

talk_RenanHirayama.pdf

14:20 On the hunt for thermal radiation with low-mass dileptons in ALICE

Electromagnetic probes such as dileptons are a unique tool for studying the space-time evolution of the hot and dense matter created in ultra-relativistic heavy-ion collisions. Such pairs, being emitted throughout the entire system evolution, carry information from the moment of their creation to the detector unperturbed by strong final-state interactions, allowing one to get a direct access to the thermal radiation from early hot stages of the collision. At the LHC energies however, this signal sits on top of large background from correlated semi-leptonic heavy-flavour decays, which makes the separation of prompt and non-prompt sources vital for the measurement of thermal radiation. The studies of dilepton production in collision systems such as proton--proton or light ions can shed light on possible onset of thermal radiation in smaller systems.

This talk will present an overview of ALICE results on the low-mass dielectron and dimuon production in pp, OO and Pb--Pb collisions at various collision energies using high-precision data collected during the LHC Run 3. The dilepton yield is systematically measured across various collision systems and is compared to the sum of all known hadronic sources. Thanks to the new inner tracking system, the dielectrons from heavy-flavour hadrons can be identified and separated from the prompt sources using a data-driven approach. Results from such an approach will be discussed in pp collisions, establishing a crucial baseline for the studies in larger collision systems.

Speaker: Jerome Jung (Goethe University Frankfurt (DE))

HP26_dielectrons_jjung_v9.pdf

14:40 The polarization of thermal dileptons emitted in high-energy heavy-ion collisions

Dileptons (virtual photons) are penetrating probes of the quark–gluon plasma (QGP), and their polarization encodes detailed information about their production mechanism. This study presents an integrated and realistic framework for calculating the production of thermal dileptons and their polarization signature, and it considers the local flow conditions of the QGP, and also compares the information carried by dielectrons to that carried by dimuons. By combining virtual photon spectral functions complete at next-to-leading order (NLO) in the strong coupling [1] with a multi-stage iEBE-MUSIC hydrodynamic simulation of Pb+Pb collisions at the LHC, we confirm significant differences between dilepton polarization at leading order (LO) and NLO [2], and show these differences to be robust against variations in the modeling of the pre-equilibrium stage. Polarization coefficients in different reference frames are examined and compared. Also included in our study is the contribution from the Drell-Yan process: an irreducible background to a dilepton signature of the QGP, in the intermediate invariant mass region. This work builds on results reported in:

[1] Jessica Churchill, Lipei Du, Charles Gale, Greg Jackson, and Sangyong Jeon, Phys. Rev. Lett. 132 (2024) 17, 172301; Phys. Rev. C 109, 044915 (2024)
[2] Xiang-yu Wu, Han Gao, Bailey Forster, Charles Gale, Greg Jackson and Sangyong Jeon, Phys.Rev.Lett. 134 (2025) 24, 242301
[3] Han Gao, Xiang-yu Wu, Greg Jackson, Charles Gale and Sangyong Jeon, in preparation.

Speaker: Prof. Charles Gale

Gale__HP_2026.pdf

15:00 Dielectron measurements of heavy-flavor production and medium radiation in p+p and Au+Au collisions by PHENIX

Dileptons, which interact only electromagnetically with the strongly coupled medium, provide penetrating probes of the space–time evolution of QCD matter created at RHIC. In the intermediate mass region ($m_\phi < m_{ee} < m_{J/\psi}$), thermal radiation from the medium competes with dielectrons originating from semi-leptonic decays of charm and bottom hadrons. A quantitative separation of the heavy-flavor contribution is therefore essential to isolate the thermal signal. In this talk, PHENIX presents new measurements of dielectron production at $\sqrt{s}=200$ GeV in p+p and Au+Au collisions using the Silicon Vertex Detector. In p+p collisions, distance-of-closest-approach (DCA) measurements combined with template fits enable an empirical separation of charm and bottom contributions to the dielectron mass spectrum and the extraction of the corresponding heavy-flavor cross sections. In Au+Au collisions, high-statistics mid-rapidity data from 2014 are analyzed using boosted decision tree–based electron identification, precise hit-to-track matching, and efficient rejection of photon conversions, resulting in a significantly improved signal-to-background ratio. By combining DCA measurements with the heavy-flavor cross sections established in p+p collisions, the thermal radiation component in Au+Au collisions can be isolated. In the intermediate mass region the thermal yield is substantial and exhibits an average temperature consistent with recent STAR measurements.

Speaker: Dr Iurii Mitrankov (Stony Brook University)

HardPorbes2026_YuM.pdf

14:00 → 15:20 Parallels: EEC

Convener: Rainer Fries (Texas A&M University)

14:00 Probing jet modifications in the QGP using Energy Correlators in Pb-Pb collisions at $\sqrt {s_\mathrm{NN}}$ = 5.02 TeV with ALICE

Energy correlators, defined as energy-weighted N-particle correlations within jets as a function of their angular separation, have emerged as powerful tools for probing jet substructure across multiple scales. These observables provide unique insights into QCD dynamics, exhibiting a clear separation between perturbative effects at large angles and non-perturbative physics at small angles in vacuum. In heavy-ion collisions, jets traversing the quark-gluon plasma (QGP) undergo interactions that modify their internal structure. Energy-energy correlators (EEC) offer a novel approach to characterize these modifications and extract microscopic properties of the QGP. Recent measurements by CMS in Pb-Pb have demonstrated that EECs are modified relative to vacuum QCD predictions, establishing them as sensitive probes of jet-medium interactions.
In this talk, we present measurements of the two-point energy correlator (EEC) in Pb-Pb collisions at $\sqrt {s_\mathrm{NN}}$ = 5.02 TeV with the ALICE detector. The EEC exhibits clear modifications in the QGP: an enhancement at small angular scales ($\sim$ 10$^{-2}$), followed by a suppression at intermediate angles and a hint of enhancement toward large angles. Comparisons with state-of-the-art theoretical models offer new opportunities to constrain jet quenching mechanisms and advance our understanding of QGP properties.

Speaker: Wenqing Fan (University of Houston (US))

HP2026_wenqing_final.pdf

14:20 In medium scale evolution of the energy-energy correlators for heavy ion phenomenology

In this work we present a first-principles analysis of the scale evolution of the two-point energy-energy correlator (EEC) for quark and gluon jets propagating through QCD matter. The EEC is a jet substructure observable that encodes the angular distribution of energy flow within jets and has proven valuable for precision tests of QCD in elementary collisions. Extending this framework to heavy-ion environments, we derive a factorized description of the in-medium EEC using Soft Collinear Effective Theory with Glauber gluon interactions, allowing systematic inclusion of medium-induced interactions. Working in the opacity expansion, we compute the medium-modified quark and gluon jet functions at one loop and perform leading-logarithmic resummation of large-scale logarithms. We find an experimentally accessible kinematic regime where medium effects manifest directly through medium-induced corrections to the anomalous dimensions, providing a transparent probe of in-medium dynamics. We also demonstrate the presence of Coulomb-logarithmic enhancements regulated by plasma screening and compare our analytic predictions with EEC measurements in p–Pb collisions and offer projections for small systems such as O-O collisions.

Speaker: Bianka Mecaj (Los Alamos National Laboratory)

Hard probes_talk.key.pdf

14:40 Sensitivity of Energy-Energy Correlators to Multiple QCD Regimes in Heavy-Ion Collisions

Energy-Energy Correlator (EEC) applications to Heavy-Ion Collisions have been the subject of numerous studies in recent years, namely in the exploration of the Quark-Gluon Plasma (QGP). EECs have been originally proposed to display an often assumed scale factorization between different QCD processes, such as perturbative and non-perturbative effects, making them particularly appealing for scale-differential heavy-ion studies. However, we show through several Monte Carlo simulation tools, including Pythia, Herwig and CoLBT-hydro, a global and non-trivial sensitivity of EECs to the different physics regimes, calling this factorization into question [1]. With experimental measurements of in-medium EECs multiplying in the past few years, we take new steps towards a comprehensive understanding of their multifactorial dependences in order to unlock their full potential as QGP probes.
[1] L. Apolinario, R. Kunnawalkam Elayavalli, N. O. Madureira, J.-X. Sheng, X.-N. Wang, and Z. Yang, Phys. Rev. D 112, 054018 (2025), arXiv:2502.11406 [hep-ph].

Speaker: Nuno Olavo Gonçalves Mendes Madureira (LIP/IST)

Sensitivity of Energy-Energy Correlators to Multiple QCD Regimes in HICs.pdf

15:00 Measurement of Two-Point Energy Correlators in Ru+Ru and Zr+Zr collisions at STAR

In relativistic ion collisions, any hard-scattered partons will undergo perturbative fragmentation and hadronization, resulting in a collimated collection of hadrons that can be measured as a jet. The N-Point Energy correlator (ENC) is a jet substructure observable formed out of the distribution of angular distances between all groups of N constituents in a jet weighted by their energy product. STAR has recently published measurement of two- and three-point energy correlators in proton+proton collisions at $\sqrt{s}$ = 200 GeV, demonstrating the ability of ENCs to isolate non-perturbative effects to specific angular scales and provide insight into the time dynamics of jets. In heavy-ion collisions, the quark-gluon plasma has been seen to quench jets and modify their substructure. Therefore, an extension of energy correlators into a heavy-ion environment can potentially isolate these modifications to identifiable angular scales, including the onset of effects such as color coherence and the medium wake. These measurements necessitate subtraction of both background-background and background-signal correlations via a novel background subtraction technique. In this talk, the first measurement of N-point energy correlators in heavy-ion (specifically Ru+Ru and Zr+Zr) collisions at $\sqrt{s_{NN}}$ = 200 GeV at RHIC will be shown. Results will be shown for jets with resolution parameter R = 0.4 and transverse jet momenta $p_{\rm T, jet} >$ 20 GeV/c in both central and peripheral collisions.

Speaker: Andrew Tamis (Yale University)

Hard_Probes_26_Talk_Final.pdf

14:00 → 15:20 Parallels: High-PT

Convener: Prof. Gojko Vujanovic (University of Regina)

14:00 Dijet probes for event-geometry biases in p+A collisions at ATLAS

Proton–nucleus collisions at the LHC provide a powerful laboratory to investigate initial-state phenomena in heavy-ion physics. Fluctuations in the proton configuration can significantly modify its effective interaction strength, biasing estimates of event activity and, consequently, the inferred number of wounded nucleons in the Pb nucleus. In this context, dijets offer a particularly sensitive probe, as they enable a precise characterization of the initial-state kinematics of the hard scattering. In this talk, we present recent ATLAS results studying the role of proton configurations in p+A collisions, using dijet events in p+Pb collisions at $\sqrt{s_{NN}}$=8.16 TeV collected in 2016. The results investigate correlations between event activity, forward neutron production, and the initial-state kinematics of the hard process, providing new evidence for the role of proton shape fluctuations in these collisions. These measurements provide the first quantitative input toward exploring the relationship between hard scattering processes and nuclear breakup. The data offer new opportunities to link proton spatial configurations, typically characterized via generalized parton distribution functions, with nuclear breakup and the overall interaction strength in p+A reactions, and provide useful insights to understand centrality biases affecting different geometry estimators in hard-scatterings.

Speaker: Radek Jirasek (Charles University (CZ))

HP2026_ATLAS_Radek_Jirasek_Dijets_eventGeometryBiases_pPb.pdf

14:20 First exploration of hard-soft correlations from IP-Glasma

We present the first self-consistent, first-principles, event-by-event framework for high-$p_T$ hadron production that incorporates correlated hard and soft particle production within a single theoretical approach. Using IP-Glasma, the model simultaneously generates the hard $\sim 10$ GeV gluon spectrum and the soft $\lesssim 3$ GeV gluon multiplicity, both subsequently hadronized, enabling a consistent treatment of centrality bias in both large and small systems. With parameters constrained by a previous Bayesian analysis of HERA data, we present predictions for the centrality-dependent nuclear modification factor in $\text{Pb} +\text{Pb}$, $p + \text{Pb}$, and $p + p$ collisions, finding good agreement with experimental trends from initial state physics. We further show that constraints from measured charged-particle multiplicity fluctuations across systems provide additional restrictions on the predicted nuclear modification factor. While the resulting $R_{pPb}$ is in good qualitative agreement with data, the model overshoots the measurements in the most central collisions, leaving room for final-state energy loss. Finally, we present predictions for the effects of centrality bias in $\text{O} + \text{O}$ and $\text{Ne} + \text{Ne}$ collisions.

Speaker: Coleridge Faraday (University of Cape Town)

ColeFaraday_HP2026.pdf

14:40 Hard Photons as Standard Candles of Centrality in Small Systems

One of the primary biases in event classification for small-system ($p/d+A$) collisions is thought to be depletion of the energy available for soft production by hard scatterings in high activity events. This may potentially mask any real suppression or enhancement in the nuclear modification factor $R_{p/d\,A}$. In this work, the X-SCAPE framework is used to simulate $d+Au$ collisions at top RHIC energy and compare with recent PHENIX data. In particular, we investigate the production of high-$p_T$ pions and direct photons with event activity and examine the QGP final-state effects on $R^{\pi^0}_{dA}$ [1]. We extend our existing hard-soft framework [2] to allow for multiple hard scatterings, while enforcing exact energy-momentum conservation between the soft and hard sectors. Hard photons are produced in the initial state, in hard scattering, and in final state radiation. We present results both with and without the inclusion of final state energy loss. This work presents the first simulation of a $p/d+A$ collision with correlated soft and hard production mechanisms, multiple hard binary collisions, and exact energy-momentum conservation.

[1] N. J. Abdulameer et al. (PHENIX), Phys. Rev. Lett. 134, 022302 (2025).
[2] I. Soudi et al. (JETSCAPE), Phys. Rev. C 112, 014905 (2025).

Speaker: Robert Dolan (Wayne State University)

Final_Hard_Probes_2026_Hard_Photons_as_Standard_Candles_of_Centrality.pdf

15:00 Measurement of two-particle correlation in high energy e+e- collisions with enhanced W⁺W⁻ contributions using the ALEPH archived data

Studies of high charged-particle multiplicity events have been a central focus in enhancing sensitivity to the possible emergence of collective-like behavior, even in e⁺e⁻ collisions. We present a measurement of two-particle angular correlations using data collected by the ALEPH detector during the LEP2 program in e⁺e⁻ collisions at center-of-mass energies up to √s = 209 GeV, with a focus on enhancing the contribution from two–color-string topologies arising from hadronic W⁺W⁻ decays using a boosted decision tree (BDT). Correlation functions are evaluated across a broad range of pseudorapidity and full azimuth, in bins of charged-particle multiplicity. The correlation functions are further decomposed into a Fourier series, and the resulting harmonic coefficients vn are compared with Monte Carlo (MC) baseline. For multiplicity starting from 30, the observed $v_2$ goes from negative to positive, which marks a sizable deviation from the MC expectations. This result facilitates understanding collective-like behavior emergence in small systems, and may provide new constraints on parton- and hadron-level interactions in particle production mechanisms.

Speaker: Yu-Chen (Janice) Chen (Massachusetts Institute of Technology)

HP2026_ALEPHee2PC_v3.pdf

14:00 → 15:20 Parallels: Small and Intermediate system

Convener: Yi Chen (Vanderbilt University)

14:00 A Breath of Fresh Air for Molière: Elastic Scatterings in OO Collisions

Jet partons can trigger high momentum-exchange $2 \rightarrow 2$ elastic scatterings (aka Molière scatterings) with quark- and gluon-like quasiparticles in QGP, making jets valuable probes with which to study the microscopic structure of QGP. We describe how we have implemented such Molière scatterings in the Hybrid Model of jet quenching. We then describe how measurements of the Soft Drop angle $R_g$ of jets are especially sensitive to the effects of Molière scatterings, which impart rare but sizable transverse kicks to jet constituents, broadening the angular separation of the hardest resolved splitting in the jet. The narrowing of $R_g$ in PbPb collisions because jets which lose the least energy are preferentially selected is a confounding effect. We show that this selection bias can be partially mitigated by selecting gamma-jet events based on the photon energy, with $R_g$ of gamma-jets in PbPb collisions broadening due to Molière scatterings as long as jets which are sufficiently softer than the photon are included.

We then show that OO collisions are a much better arena in which to study Molière scatterings and the microscopic structure of QGP, because although jets do lose energy they lose less energy, resulting in less selection bias. We show that agreement with CMS data of charged-hadron $R_{AA}$ in OO collisions is obtained only when both energy loss and Molière scatterings are included in the Hybrid Model. We then show that because the confounding effects of selection bias are minimal, a genuine broadening of $R_g$ stands out in OO collisions even for inclusive jets: we see more anti-$k_t$ $R = 0.4$ jets with $R_g>0.2$ in OO collisions compared to pp collisions. We find complementary and consistent results via energy–energy correlator (EEC) measurements in OO collisions, showing that they exhibit enhanced large-angle correlations driven by elastic scatterings with minimal confounding effects from selection bias.

Speaker: Arjun Srinivasan Kudinoor (Massachusetts Institute of Technology)

Arjun_Kudinoor_HP_2026.pdf

14:20 Unraveling Jet-medium Interaction with Energy Correlators in Relativistic Oxygen Collisions

Jets produced in a relativistic collision of oxygen nuclei plow through and interact with the droplet of quark-gluon plasma formed in the same collision. As they traverse a droplet of QGP, high-energy partons within these jets lose energy to and excite wakes in the QGP, and elastically scatter off of quark- and gluon-like quasiparticles in the QGP droplet. All these interactions modify the substructure of jets in OO collisions. Since energy-energy correlator (EEC) observables are especially useful for studying the correlations of energy flow within jets, they serve as useful tools to reveal the presence of and to study the impact of jet-wakes and elastic scatterings between jet-partons and medium-quasiparticles in OO collisions.

In this poster, we shall provide a full presentation of a suite of Hybrid Model calculations of EECs for jets with varying $p_T$ and radii in OO collisions. Since the energy lost by jets due to strongly coupled interactions with the medium is smaller in OO collisions than in PbPb collisions, we show that EECs suffer far less from jet-energy selection biases in OO collisions. Although jets in OO collisions lose less energy than jets in PbPb collisions, jet-induced wakes and elastic scatterings modify the substructure of jets in OO collisions enough to significantly enhance EECs at large angular separations ($R_{L}$) between jet-constituents. The largest enhancements are seen for values of $R_{L}$ between $R_{\rm jet}$ and $2R_{\rm jet}$, as correlations at these angles within jets are dominated by correlations among particles originating from elastic scattering and jet wakes.

We show that increasing the jet-radius allows one to amplify the effects of jet-induced wakes. These effects can be suppressed, allowing the effects of elastic scatterings to dominate and making them easy to isolate, either by reducing the jet-radius or by calculating EECs using only those hadrons with $p_{T} > 2$ GeV, since hadrons originating from jet wakes are soft. Therefore, EECs in OO collisions are promising observables to reveal the presence of, to separate, and to study the nature of both jet-induced wakes and elastic scatterings.

Speaker: Arthur Lin

Arthur-Lin-HP-2026.pdf

14:40 Azimuthal anisotropy of charged particles with transverse momentum up to 50 GeV in OO collisions from the CMS detector

The average $N_{part}$ and $N_{coll}$ are similar between minimum-bias OO collisions and peripheral PbPb collisions with 70-90% centrality. After accounting for event selection and geometric biases, no significant jet quenching is observed in 70–90% PbPb collisions. In marked contrast, a clear signature of jet quenching is observed in minimum-bias OO collisions. This difference, despite comparable system size, motivates a detailed study of high $p_{T}$ azimuthal anisotropy in OO collisions to directly probe the path-length dependence of parton energy loss. In this talk, we present measurements of the azimuthal anisotropy coefficients $v_{n}$ for charged particles with $p_{T}$ up to 50 GeV in OO collisions using the CMS detector. The analysis is performed with the scalar-product method over multiple centrality intervals. Nonflow contributions are systematically investigated by varying the pseudorapidity gap between charged particles measured in the tracker and reference particles in the hadronic forward calorimeters. These results provide critical constraints on the onset of jet quenching in light-ion systems and offer a unique bridge for understanding the evolution of energy loss from small to large systems.

Speaker: Shengquan Tuo (Vanderbilt University (US))

hp2026_Tuo_v7.pdf

15:00 Probing Parton Energy Loss with Dijets and Jet Azimuthal Anisotropies in Light-Ion Collisions with ATLAS

Light-ion collisions at the LHC provide access to parton energy loss in compact systems with a controlled initial geometry and a direct pp baseline at the same energy. In 2025, ATLAS recorded $8~\mathrm{nb}^{-1}$ of O+O and $1~\mathrm{nb}^{-1}$ of Ne+Ne collisions at $\sqrt{s_{\mathrm{NN}}}=5.36~\mathrm{TeV}$, matching a previously collected $400~\mathrm{pb}^{-1}$ $pp$ reference sample. Using anti-$k_t$ $R=0.4$ jets, ATLAS measured the dijet transverse momentum balance in O+O collisions via the distribution of $x_J~\equiv~p_{\mathrm{T},2}/p_{\mathrm{T},1}$ for back-to-back dijets with $63 < p_{\mathrm{T},1} \leq 251~\mathrm{GeV}$ as a function of event activity. A centrality-dependent modification of the $x_J$ distributions is observed in O+O relative to $pp$, with the largest modification in the most central O+O events, consistent with Pb+Pb results at comparable event activity. In the same light-ion datasets, ATLAS quantified the geometric dependence of jet quenching by measuring jet azimuthal anisotropies $v_n$ in O+O and Ne+Ne collisions. Together, the dijet-balance and jet-$v_n$ observables provide complementary constraints on the magnitude of energy loss and its path-length dependence in light nuclear collision systems at LHC energies.

Speaker: Rafet Kavak (CERN)

rafet_kavak_HP2026_23June2026.pdf

15:20 → 15:50 Coffee break

15:50 → 17:10 Parallels: EEC

Convener: Dr Yang-Ting Chien (Georgia State University)

15:50 Measurements of track energy-energy correlators and one-point charge correlation in $e^{+}e^{-}$ collisions using DELPHI open data

Recent theoretical progress has enabled precision calculations of energy flux on charged particles alone, allowing data-theory comparisons for measurements using high-quality tracking detectors. We present a measurement of the energy-energy correlator using charged particles with high angular resolution in $e^{+}e^{-}$ at $\sqrt{s}=91.2~\mathrm{GeV}$, using the newly released DELPHI Open Data. Our results are compared to record-precision theoretical predictions, at NNLL accuracy in the collinear region and NNNNLL accuracy in the back-to-back region, covering the full spectrum of the correlator and probing QCD over three orders of magnitude in scale. It reveals interesting emergent phenomena, including light-ray quasi-particle states, flux-tube excitations, and their transitions into confined hadrons. The measurement establishes a new benchmark for energy-flux measurements in small systems and provides an important reference for energy correlators in heavy-ion collisions. This work constitutes the first physics analysis based on DELPHI Open Data and, by leveraging the preserved DELPHI detector simulation and reconstruction chain, provides an end-to-end experimental landmark for precision studies with archived collider datasets.

Speaker: Jingyu Zhang (Vanderbilt University (US))

260623-HardProbes.pdf

16:10 sPHENIX studies of QCD radiation in p+p collisions with energy-energy correlators and underlying event production

Energy-energy correlators (EEC) have emerged as powerful observables in high-energy physics, offering a direct probe of the virtuality scale and a clean theoretical framework for comparisons with pQCD. This talk will present a novel study of whole event Energy-Energy Correlators (wEEC) in a high-statistics sample of di-jet events selected in sPHENIX proton+proton data at 200 GeV. The measurement correlates the energies of all calorimeter towers in the event, extending the reach beyond the jet cone and enabling sensitivity to both intra-jet and inter-jet structure, using several wEEC variants and multi-differential measurements of the transverse EEC (TEEC). Separately, this talk presents a new measurement of the transverse energy in the region transverse in azimuth to the leading jet, following more traditional approaches used at RHIC and the LHC for understanding the systematics of soft particle production associated with a high-pT jet. The results include comparisons to event generators and measurements at other center-of-mass energies. Together, these observables probe correlations over a broad range of angular scales and provide insight into the interplay between perturbative jet fragmentation and additional activity from multiple parton interactions at RHIC energies.

Speaker: Skaydi Grossberndt

Quantifying Soft-Hard Correlations with underlying event and Energy-Energy.pdf

16:30 Collinear limit of Energy-Energy Correlators in pp and pA collisions

Energy-energy correlators (EECs) are event-shape observables that can be used to study QCD by examining angular correlations between produced particles. As the EEC is weighted by the energy of the outgoing particles, it is an infrared-safe observable that is less sensitive to physics at the nonperturbative scales. The energy weight also allows one to exploit the momentum-sum rule of fragmentation functions, making the EEC less sensitive to the nonperturbative hadronization in the final state and allowing one to zoom in on other aspects of the collision process.

Very recently, there has been an intense effort to describe the modifications of this observable due to the presence of a color medium, with the ultimate goal of using EECs to probe the properties of QCD matter. In this talk, we present a non-perturbative model that allows us to describe EECs in the entire collinear region of the current hadronic experiments, encapsulating both the perturbative and non-perturbative contributions at the same time [1]. With this, we get an excellent agreement with ALICE and CMS experimental data for pp collisions. In addition, we include modifications from the nuclear medium to describe pA collisions, recovering the observed trend in recent ALICE measurements.

[1] João Barata, Zhong-Bo Kang, Xoán Mayo López, JP, Phys.Rev.Lett. 134 (2025) 251903 (arXiv:2411.11782 [hep-ph])

Speaker: Jani Penttala (UCLA)

2026_Hard_probes_Penttala.pdf

15:50 → 17:10 Parallels: HF and Quarkonia

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

15:50 sPHENIX new measurements of heavy flavor hadronization in p+p collisions at RHIC

sPHENIX is a next-generation experiment at RHIC for jet and heavy-flavor physics which was fully commissioned in 2024. Using its novel streaming-readout-capable, precision tracking system, sPHENIX collected over 10 pb$^{-1}$ of unbiased p+p collisions, and over 6.5 nb$^{-1}$ of minimum-bias Au-Au collisions. Key goals of the sPHENIX heavy flavor physics program include measurements of the ratios of heavy flavor hadron yields, in both Au+Au and p+p collisions. These measurements, such as comparisons of the $\Lambda_c$ to $D^0$ and the $D_s^+$ to $D^+$ differential yields, probe questions related to the hadronization of heavy-flavor baryons compared to mesons and of strangeness enhancement in the charm sector, both in the Quark-Gluon Plasma medium and in vacuum. For example, there are no previous measurements of the $\Lambda_c$/$D^0$ and $D_s^+$/$D^+$ baselines in p+p collisions at RHIC energies, modern Monte Carlo event generators give widely different predictions, and the ratios in Au+Au at RHIC are only poorly known. This talk presents the progress towards new measurements from sPHENIX of the first $\Lambda_c$/$D^0$ and $D_s^+$/$D^+$ ratios in p+p collisions at RHIC.

Speaker: Benjamin Kimelman (Vanderbilt University)

Kimelman_HP2026_Final.pdf

16:10 Strangeness effects on heavy-quark hadronization from small to large systems with ALICE

At the extreme temperature and energy-density conditions reached in ultrarelativistic heavy-ion collisions, nuclear matter is expected to undergo a phase transition to a color-deconfined state known as the quark–gluon plasma (QGP). In this environment, charm quarks can hadronize not only through vacuum fragmentation, as in leptonic collisions, but also via recombination with light partons from the medium, in particular, strange quarks that are thermally produced in the QGP. This mechanism leads to an enhanced production of charm hadrons containing strange quarks relative to non-strange species, a phenomenon commonly referred to as strangeness enhancement and widely regarded as a hallmark of QGP formation.

Ratios of strange-to-non-strange charm hadrons, therefore constitute powerful observables to probe heavy-quark hadronization mechanisms. A consistent interpretation of these ratios further requires accounting for feed-down contributions from excited charm–strange states, whose decay channels populate both strange and non-strange ground-state charm hadrons.

This contribution presents a comprehensive measurement of the $\mathrm{D_s^+/D^+}$ production ratio over a wide range of collision systems, spanning from low-multiplicity pp collisions at $\sqrt{s}=13.6$ TeV to high-multiplicity Pb–Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.36$ TeV. The first measurement of the transverse-momentum-differential production cross sections of the orbitally excited $\mathrm{D_{s1}(2536)^+}$ and $\mathrm{D_{s2}(2573)^{*+}}$ mesons in pp collisions at $\sqrt{s}=13.6$ TeV is reported, together with the production ratios relative to the $\mathrm{D_s^+}$ ground state. Finally, the first measurement of ${\Xi_\mathrm{c}^0}$-baryon production in Pb–Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV is presented, and the ratios of its yield to those of strange and non-strange charm mesons and baryons are reported in central and semicentral collisions.

Speaker: Maria Fernanda Torres Cabrera (University of Houston (US))

HP_Nashville_26_FT_Final.pdf

16:30 Heavy-flavour production in fixed-target mode at LHCb

Quarkonium production in hadronic collisions is a key observable for studying the interaction of heavy quarks with the nuclear medium. Depending of the collision system size, quarkonia can be affected by a combination of hot and cold nuclear effects, which can only be disentangled with a systematic study with systems of different sizes and geometries. By studying the production of ground and excited states, final-state effects such as nuclear absorption or interaction with comovers can be distinguished from those due to modifications in the partonic initial states of the colliding nuclei. LHCb's fixed-target configuration provides a perfect environment for these studies, creating the possibility of using different gaseous targets with proton and ion colliding beams at an energy range of $\sqrt{s_{\mathrm{NN}}}\sim100\,\mathrm{GeV}$. The system has been recently upgraded for Run 3 allowing for the injection of new targets (hydrogen, deuterium) and dramatically larger luminosities with respect to Run 2. These improvements enable new measurements, such as differential studies of $\psi(2S)$ production and access to rarer $\Upsilon$ states. In this talk, we will present first measurements quarkonium production in fixed-target collisions with SMOG2, improving our understanding of QCD in nuclear environments.

Speaker: Juliette Authier (Laboratoire Leprince-Ringuet, CNRS (FR))

HardProbes_JulietteAuthier_v2.pdf

15:50 → 17:10 Parallels: Substructure

Convener: Gunther Roland (Massachusetts Inst. of Technology (US))

15:50 Measurement of subjet fragmentation in pp and Pb--Pb collisions with ALICE

Jets provide calibrated hard probes of the quark–gluon plasma (QGP), with their production and vacuum evolution constrained by perturbative QCD calculations. Jet substructure observables, such as the momentum fraction carried by the leading (or inclusive) subjet, $z_r$, are directly sensitive to the hardest branchings of the parton shower and offer a robust, theoretically controlled handle on shower dynamics. Comparisons of $z_r$ between pp and Pb--Pb collisions probe medium-induced modifications of jet fragmentation and test the extent to which fragmentation universality persists in the presence of a QGP.

We present measurements of inclusive and leading-subjet fragmentation in pp collisions at $\sqrt{s}=5.36$ TeV with ALICE. The substantially larger Run 3 dataset enables improved precision and extends the kinematic reach of previous measurements to higher jet $p_{\mathrm{T}}$, providing the missing pp reference for direct comparison to Run 2 Pb--Pb results. We will present the Pb--Pb/pp ratio using the new baseline, which allows us to leverage the full kinematic range of the Pb--Pb measurement. The measured $z_r$ distributions are confronted with theoretical calculations that implement different in-medium shower evolution scenarios and account for changes in quark/gluon jet composition.

Speaker: Luisa Bergmann (University of California Berkeley (US))

HP2026_bergmann.pdf

16:10 Groomed Jets in Heavy-Ion Collisions with an NLO-Accurate Vacuum Baseline

We present the first study of groomed jet observables in heavy-ion collisions based on a jet-quenching simplified framework with a next-to-leading order (NLO) accurate vacuum baseline. Establishing such a baseline is essential for disentangling genuine medium-induced effects from biases inherent to jet selection and grooming procedures.

Using NLO matrix elements consistently matched to a leading-logarithmic parton shower, we construct a controlled reference for proton–proton collisions and embed colour coherence effects as the sole source of medium modification. This minimal setup allows us to isolate the role of coherence in shaping groomed jet observables, independently of uncontrolled modelling assumptions.

We show that this framework provides a robust description (within 10%) of recent ALICE and ATLAS groomed jet measurements and demonstrates that improving the vacuum baseline is a prerequisite for precision jet-quenching phenomenology. Our results establish a new reference point for the interpretation of groomed jet observables in the upcoming heavy-ion programme at the LHC.

Speaker: Diogo Costa (Granada University)

HardProbes26_DiogoCosta.pdf

16:30 Probing jet quenching via jet substructure measurements in Pb+Pb collisions with ATLAS

In ultra-relativistic collisions of large nuclei, the yield of jets - the colorless remnants of hard-scattered partons - is found to be suppressed relative to baseline proton-proton collisions. This suppression, known as jet quenching, owes its origins to partonic energy loss as quarks and gluons traverse the hot, dense quark-gluon plasma medium during the early stages of nuclear collisions. While quenching effects have long been measured as a function of the jet momentum, this ATLAS talk presents a set of ATLAS measurements which focus on the relationship between jet quenching and the process of jet fragmentation itself through the use of substructure observables. These include measurements of substructure of large-radius jets, studies of jets recoiling against isolated photons, and measurements of jet suppression performed differentially for different jet radii. The jet quenching is quantified via the use of the nuclear modification factor, $R_{AA}$, and is measured as a function of centrality, jet transverse momentum, and substructure observables that make use of a variety of inputs from the ATLAS detector.

Speaker: Anne Marie Sickles (Univ. Illinois at Urbana Champaign (US))

sickles_062326.pdf

16:50 Multiplicity distributions in QCD jets and large-radius jet suppression with substructure dependence at the LHC

In this talk, we first investigate the virtuality evolution of QCD jets, with a particular focus on parton multiplicity distributions evolving from an initial jet virtuality down to an infrared scale $Q_0$, which can be interpreted as the hadronization scale in $pp$ collisions. As a concrete test of this framework, we present a systematic study of Koba-Nielsen-Olesen (KNO) scaling for jets produced in $pp$ collisions at the LHC. By incorporating energy conservation within the Double Logarithmic Approximation (DLA), our results provide a good description of the inclusive charged-particle multiplicity distributions of the two leading jets in $pp$ collisions at $\sqrt{s} = 13~\mathrm{TeV}$, as measured by ATLAS over a broad jet transverse-momentum range of $0.1-2.5~\mathrm{TeV}$.

We then extend this framework to heavy-ion collisions by combining BDMPS-Z energy loss with the vacuum-like virtuality evolution of parton multiplicity distributions in QCD jets through color decoherence. In this context, the scale $Q_0$ is identified as the characteristic virtuality scale governing color coherence and decoherence. Using this approach, together with a $(2+1)$-dimensional OSU hydrodynamic model of the QCD medium, we perform detailed calculations of large-radius jet suppression and its substructure dependence in PbPb collisions at $\sqrt{s_{\rm NN}} = 5.02~\mathrm{TeV}$. We find that, after fixing the only two parameters of the framework, the initial jet quenching parameter $\hat{q}_0$ and $Q_0$, through independent jet-quenching observables, our predictions for jet substructure observables with single- and multi-subjet configurations are in good agreement with ATLAS data. These results highlight the essential roles played by virtuality evolution and color decoherence in jet quenching.

[1] X.-P. Duan, L. Chen, G.-L. Ma, C. A. Salgado, and B. Wu, Phys. Rev. D 112, 094022 (2025).
[2] X.-P. Duan, L. Chen, G.-L. Ma, C. A. Salgado, and B. Wu, arXiv:2509.06158.
[3] X.-P. Duan, L. Chen, G.-L. Ma, C. A. Salgado, and B. Wu, work in progress.

Speaker: Xiang-Pan Duan

15:50 → 17:10 Parallels: Small and Intermediate system

Convener: Prithwish Tribedy (Brookhaven National Lab)

15:50 Photon+hadron correlations and probes of collectivity in light ion collisions with ATLAS

Oxygen-oxygen (O+O) and Neon-neon (Ne+Ne) collisions offer a unique opportunity to observe the onset of significant parton-QGP interactions which lead to parton shower modification, and to investigate such effects in the presence of the smaller event backgrounds provided by light ion collisions. At the same time, systematic measurements of multiplicity, mean pT, and collective flow (quantified via the azimuthal anisotropy coefficients $v_n$) provide valuable insight into these event backgrounds, resulting from the interplay between the initial-state geometry, energy deposition processes and their evolution to the final state. This talk will report two-particle correlations, $v_n\{2\}$, and four-particle correlations, $v_n\{4\}$,  measured in Ne+Ne and O+O collisions.  Comparison of these results indicate that the elongated nuclear structure of neon leads to an enhanced $v_2\{k\}$ in the most central Ne+Ne collisions relative to those of O+O.  New O+O and Ne+Ne measurements will also be presented of the charged particle pseudorapidity density ($dn/d\eta$) and average transverse momentum ($\langle p_\mathrm{T}\rangle$), measured over the fiducial kinematic range $|\eta| < 2.5$ and $0.27 < p_\mathrm{T} < 5$\,GeV. The flow, multiplicity and pT measurements are compared to the results of hydrodynamic calculations using different models of the initial state, providing a comprehensive first view of these two small systems. Finally, this talk presents a new measurement of gamma+hadron correlations in O+O collisions, probing the modification of the parton shower, and the resulting hydrodynamization of the lost energy, for the first time in this collision system. Results are reported for photons with $p_\mathrm{T} > 30$ GeV, hadrons with $p_\mathrm{T} > 1$ GeV, and as a function of the O+O collision centrality, and include comparisons to a variety of state-of-the-art jet energy loss models.

Speaker: Blair Daniel Seidlitz (Columbia University (US))

BSeidlitz_lightIons.pdf

16:10 Probing parton energy loss via identified strange hadrons (K^0_S and Lambda) in OO collisions at \sqrt{s_{NN}} = 5.36 TeV with CMS

High-momentum charged particles originate from the fragmentation and hadronization of partons that undergo hard scattering, and their yields are consequently sensitive to parton energy loss in the QGP. The presence of such energy loss in small collision systems has long been an open question in heavy-ion physics. Recently, the CMS experiment reported a significant suppression of charged-particle production in oxygen–oxygen (OO) collisions at \sqrt{s_{NN}} = 5.36 TeV, providing a first indication of parton energy loss even in intermediate-size systems. To further probe this phenomenon, we study identified-strange hadrons, K^0_S and Lambda, which are particularly sensitive to hadronization dynamics. In the intermediate transverse momentum region, (2 < pT < 5 GeV), when the dominant particle production mechanism transitions from soft processes to hard scattering, effects from radial flow and quark coalescence become important. We present the first measurement of the nuclear modification factor of identified strange hadrons, K^0_S and Lambda, in OO collisions at \sqrt{s_{NN}} = 5.36 TeV, providing new insights into the flavor dependence of parton energy loss and the role of strangeness in the QGP medium.

Speaker: Sruthy Jyothi Das (University of Illinois Chicago (US))

sjdas_20260623_HP2026.pdf

16:30 Observation of jet quenching in O+O collisions at $\sqrt{s_{\mathrm {NN}}}$ = 200 GeV with the STAR experiment at RHIC

Measurements of hard probes in O+O collisions are crucial for elucidating the limit of system size where the jet quenching signal is observable. To achieve high precision for such measurements one needs to minimize model dependence, selection bias, and nuclear parton distribution function (nPDF) effects. In this regard, coincidence observables provide particular advantages. We present measurements of charged di-hadron correlations (h--h) and the semi-inclusive distribution of charged-particle jets recoiling from a trigger hadron (h--jet) in O+O collisions at $\sqrt{s_{\rm NN}} = 200~\mathrm{GeV}$. High-transverse-momentum triggers ($7 < p_{\rm T} < 30~\mathrm{GeV}/c$) and recoiling hadrons ($3 < p_{\rm T} < 7~\mathrm{GeV}/c$) or jets ($p_{\rm {T,\ jet}} > 8~\mathrm{GeV}/c$) are used. Using high event activity (EA), quantified by forward detector multiplicity and indicating more violent collisions where QGP formation is expected to maximize potential jet quenching signal, we observe significant suppression of hard probes relative to low-EA events, providing strong evidence for jet quenching in O+O collisions. The significance of the observed suppression relative to different baselines, including unity, data-driven reference, and nPDF calculations is assessed. Comparisons to similar results from collision systems of different sizes will also be shown.

Speakers: Maowu Nie (Shandong University (CN)), Dr Maowu Nie (Shandong University (SDU))

20260623_HP_v4.pdf

16:50 Jet Suppression and Azimuthal Anisotropy in O+O Collisions from RHIC to the LHC

The search for quark–gluon plasma (QGP)-like collectivity in small collision systems remains a central goal of high-energy nuclear physics. Recent results from O+O collisions suggest that strongly coupled, near-perfect-fluid behavior may emerge even in such small systems, motivating a detailed investigation of jet quenching at reduced system size. In this work, we study hadron and jet suppression in O+O collisions at RHIC energy $\sqrt{s}$ = 200 GeV to systematically quantify jet energy loss and jet anisotropic flow within the Linear Boltzmann Transport (LBT) model, coupled to an event-by-event (3+1)D hydrodynamic background. We further present predictions for jet energy loss in O+O collisions at the LHC energy $\sqrt{s}$ =5.36 TeV, enabling a unified comparison of jet suppression and jet $v_n$ across disparate energy scales. Finally, by combining the O+O results with corresponding Pb+Pb calculations, we examine the path-length dependence of jet quenching and assess how medium size and geometry control the observed suppression and anisotropy.

Speaker: Cheng Xu (South China University of Technology)

HP2026_06_23_C.Xu.pdf

18:00 → 20:00 Poster session

19:40 $\Lambda$ polarization measurements at LHCb

The LHCb detector provides a unique environment for investigating spin dynamics and hadronization in high-energy collisions owing to its precise vertex reconstruction and advanced particle identification. Studies of baryon polarization in unpolarized proton-nucleus collisions probe how quark spins contribute to the final-state hadron, shedding light on parton spin transfer and fragmentation mechanisms. Charm-baryon polarization measurements are particularly sensitive to heavy-quark spin transfer, while light-baryon polarization explores spin effects in the hadronization of light quarks. This contribution presents recent LHCb measurements of baryon polarization using both fixed-target and collider data, and discusses their impact on our understanding of hadronization mechanisms, spin transfer, and transverse-momentum-dependent fragmentation functions.

Speaker: Devon Alexander Loomis (Los Alamos National Laboratory (US))

19:40 $\phi$ and $\Omega$ production in heavy ion collisions via recombination of jet parton showers

We investigate the production of $\phi(1020)$ mesons and $\Omega(1672)$ baryons in central (0–10\%) Pb–Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV at midrapidity ($|y|<0.5$), focusing on their transverse-momentum spectra, elliptic flow $v_{2}$, and nuclear modification factor $R_{AA}$. The study is performed within a hybrid hadronization framework that combines parton recombination and fragmentation, enabling a unified description of soft and hard processes in heavy-ion collisions.

Thermal partons in the quark–gluon plasma are modeled using a blast-wave parameterization incorporating collective radial flow, while hard and semi-hard shower partons are generated with HIJING and evolved through the medium using Q-PYTHIA to account for parton energy loss. Hadron formation proceeds via recombination of thermal and shower partons, supplemented by fragmentation of remnant shower partons at high transverse momentum. The analysis is carried out on an event-by-event basis.

The transverse-momentum spectra of $\phi$ mesons and $\Omega$ baryons are decomposed into contributions from thermal–thermal, thermal–shower, and shower–shower recombination, as well as fragmentation. We evaluate the elliptic flow coefficients $v_{2}(p_T)$ to examine the collective behavior of strange and multi-strange hadrons and to explore the transfer of partonic anisotropy to final-state hadrons through recombination. The nuclear modification factors $R_{AA}(p_T)$ are obtained by comparing Pb–Pb results with proton–proton baselines generated consistently within the same framework.

Our results indicate that recombination involving strange thermal partons dominates $\phi$ and $\Omega$ production in the intermediate-$p_T$ region, leading to sizable elliptic flow and characteristic modifications of the spectra relative to proton–proton collisions. At higher $p_T$, fragmentation becomes increasingly important. Detailed comparisons with ALICE measurements at the LHC demonstrate that the hybrid recombination–fragmentation approach captures key features of strange hadron production and provides insight into strangeness hadronization and the interplay between soft and hard dynamics in the hot and dense QCD medium.

Speaker: Prof. Kyong Chol Han (Prairie View A & M University)

Han_Hard_Probes2026.pdf

19:40 $J/\psi$ elliptical-flow $v_2$ analysis in OO collisions at midrapidity using ALICE Run-3 data

Oxygen-oxygen (OO) collisions offer a unique opportunity to investigate collectivity and signatures of the medium formed in a smaller collision system compared to the heavy-ion systems such as Pb--Pb. The elliptic flow coefficient $v_2$ is a key observable sensitive to the initial collision geometry and the subsequent evolution of the system. In this context, quarkonia, and in particular the $J/\psi$ meson, are excellent probes of the medium due to their early production and their interaction with the surrounding medium. Collisions of light nuclei further allow exploration of whether charm quarks exhibit signs of thermalization in small systems. By comparing the $J/\psi$ $v_2$ measurements in OO collisions with measurements from larger collision systems, the scaling of quarkonium collectivity with system size can be explored.

In this contribution, the first measurement of the azimuthal-anisotropy coefficient $v_2$ of inclusive $J/\psi$ in OO collisions at $\sqrt{s_{NN}}$ = 5.36 TeV at midrapidity using the ALICE experiment data will be presented. The $v_2$ values are extracted in several transverse-momentum and centrality intervals using the scalar product method. The contribution outlines the full analysis procedure including the signal extraction and flow determination.

Speaker: Ankur Yadav (University of Bonn (DE))

2026-06-15-Yadav_HP_2026_Poster_0.pdf

19:40 A multi-scale approach to jet reconstruction

Jet reconstruction in A+A collisions is challenging due to high particle multiplicities and energy loss from jet-medium interactions. Conventional reconstruction methods are often limited in efficiency, particularly for low-momentum jets. Wavelet-based approaches provide an event-by-event multiscale decomposition that separates localized jet-like structures from diffuse background while preserving correlations across length scales. In this research, we present a performance evaluation of wavelet-based jet reconstruction in p+p and A+A collisions, focusing on reconstruction accuracy, background sensitivity, robustness across momentum scales, and implications for low-momentum jet measurements in heavy-ion environments.

Speaker: Ethan Fajardo (Graduate Student)

19:40 A quantification of in-jet azimuthal asymmetry for jets in e+e- collisions at 91.2 GeV using the archived ALEPH data

We present a novel measurement of in-jet azimuthal asymmetry in $\sqrt{s}=91.2\,\mathrm{GeV}$ $e^+e^-$ collisions, providing a precision vacuum reference and a controlled bridge to QGP-like collectivity. Using ALEPH data and validated simulations, we extract fully-unfolded, per-jet constituent Fourier harmonics $V_n$ ($n=1\text{-}3$) with respect to the jet axis. We compare the Winner-Take-All axis (defined by WTA recombination and aligned with the hardest branch) and the E-scheme axis (defined by the vector sum of in-jet constituent four-momenta) to quantify sensitivity to soft jet constituents, and we benchmark the results against multiple modern event generators. To study possible flow-driven effects on these observables, we use a dedicated Monte Carlo framework that injects a tunable flow-like modulation at the constituent level and measures the corresponding response. Future prospects and extensions of this study will also be discussed.

Speaker: Kuan Lu (Vanderbilt University)

HardProbes_Jun23_Luke_JetDrift.pdf

19:40 Anisotropic flow of charmonium states in relativistic heavy ion collisions

We discuss anisotropic flow, or elliptic and triangular flow of the J/ψ, ψ(2S), and χc1(1P) in relativistic heavy ion collisions based on the coalescence model. Starting from the investigation on transverse momentum distributions of the above charmonium states, we calculate their elliptic and triangular flow when they are produced by quark recombination. By not only incorporating the Gaussian source in space into the phase space distributions for charm quarks but also taking into account the expansion of the system to elliptic and triangular shapes in heavy ion collisions, we find different elliptic and triangular flow for the J/ψ, ψ(2S), and χc1(1P). We show that the wave function distribution of charmonium states plays a significant role, leading to different transverse momentum distributions as well as different elliptic and triangular flow for different charmonium states, and thereby providing plausible reasons for recent measurements by the CMS Collaboration on different elliptic flow between the J/ψ and ψ(2S).

Speaker: Sungtae Cho

19:40 Anisotropic time evolution of sound modes in Bjorken expanding holographic plasma

The speed of sound is a key parameter for characterizing equilibrium states. However, sound waves change their properties when propagating through rapidly evolving anisotropic media, such as the quark-gluon plasma created in heavy-ion collisions. This paper uses N = 4 Super-Yang-Mills theory to numerically study the time evolution of the speed and attenuation of sound modes along with the relaxation time in a plasma undergoing Bjorken expansion from various initial states in a quasi-static approximation. The longitudinal Bjorken expansion breaks the isotropy, resulting in two distinct sound speeds that range from the conformal value to the speed of light. An anisotropic hydrodynamic description is constructed and its applicability is discussed. Implications for the analysis of heavy ion data are considered.

Speaker: Mr Jun Zhang (The University of Alabama)

Zhang_Kaminski_Poster_HP26.pdf

19:40 Anti-$k_T$ jet spectra measurement for small- and large-size jets up to R = 1.2 using $e^+e^-$ collisions at 91.2 GeV with the ALEPH archived data

Many modern jet clustering algorithms, such as the anti-$k_T$ algorithm, were proposed after LEP had concluded. This poses a unique opportunity and challenge for analyzing the archived $e^+e^-$ data from the LEP era. Jets are re-clustered with the $e^+e^-$ variant of the anti-$k_T$ algorithm across a wide range of resolution parameters, ranging from 0.1 to 1.2. As a clean test of jets and QCD without the complication of hadronic initial states, electron-positron collisions serve as a benchmark to compare with analogous measurements in heavy-ion collisions, and examining jet productions with different resolution parameters is a way to probe parton shower and hadronization mechanisms. We will discuss the methodologies to calibrate jets developed specifically for $e^+e^-$ collisions. In addition, unfolding processes are carried out for ALEPH $e^+e^-$ data samples with various resolution parameters. The unfolding procedure is solidified with unfolding PYTHIA 6.1 simulation samples. Comparison between unfolded ALEPH data and simulation from various generators, including PYTHIA 8, SHERPA, HERWIG, and PanScales, are presented. We will also discuss potential future work.

Speaker: Shuangyi Zhou (Vanderbilt University)

2026HardProbeJetESpectraRdependence_BillZ.pdf

19:40 Bayesian parameter estimation for PbPb at sqrts= 5 TeV Using an SPH hydrodynamic code

We present a preliminary Bayesian parameter estimation study of Pb+Pb collisions at √sₙₙ = 5.02 TeV using the NuclearConfectionery framework, which combines Trento initial conditions, CCAKE 2.0 viscous hydrodynamics, BQSSampler particlization, and the SMASH hadronic afterburner. Gaussian Process Emulators trained on 176 design points were used to model charged-particle multiplicities, mean transverse momentum, and flow harmonics. Posterior distributions obtained through MCMC sampling indicate that the shear viscosity η/s and nucleon width are reasonably constrained, while the freeze-out temperature remains weakly constrained. These results provide a baseline for future higher-statistics analyses.

Speaker: Surkhab Kaur

Hard Probes - Surkhab.pdf

19:40 Bottomonium transport in a strongly coupled quark-gluon plasma

We present a comprehensive transport study of bottomonium production in ultra-relativistic heavy-ion collisions, based on a semiclassical rate-equation framework embedded in a realistic (3+1)D viscous hydrodynamic description of the expanding quark-gluon plasma (QGP) [1]. The in-medium reaction rates are constructed from a nonperturbative $T$-matrix approach, constrained by lattice-QCD inputs and consistent with heavy-quark diffusion phenomenology, thereby providing a unified description of open and hidden bottom dynamics in a strongly coupled QGP. The time evolution of bottomonium states is evaluated along hydrodynamic trajectories, with regeneration implemented through an equilibrium limit determined by in-medium binding energies and bottom-quark fugacities. This framework allows for a quantitative assessment of the interplay between primordial suppression and regeneration for different bottomonia. We compare our calculations with LHC data for Pb–Pb collisions at $\sqrt{s}_{NN}$=5.02\,TeV, including centrality, transverse-momentum, and rapidity dependences of nuclear modification factors. The nonperturbative in-medium interactions enhance both suppression and regeneration reactions, where the latter provide substantial contributions to the inclusive bottomonium yields.

[1] B. Wu and R. Rapp, Bottomonium transport in a strongly coupled quark-gluon plasma, arXiv 2508.20995 [nucl-th], submitted to Phys. Lett. B

Speaker: Dr Biaogang Wu (Cyclotron Institute, Texas A&M University)

poster.pdf

19:40 Calibration and Performance Studies of the sPHENIX Hadronic Calorimeter Using Cosmic-Ray Muons and LED Monitoring

Precise and stable energy calibration of hadronic calorimeters is essential for reliable jet and energy measurements in high-energy nuclear collisions. In the sPHENIX experiment, the hadronic calorimeter (HCAL) consists of an inner (IHCal) and an outer (OHCal) section, composed of scintillating tiles interleaved with absorber plates and read out via wavelengthshifting fibers coupled to silicon photomultipliers (SiPMs), whose response varies with operating conditions such as temperature. Continuous calibration and performance monitoring are therefore required to ensure detector stability.

In this poster, we present calibration studies of the sPHENIX HCAL using cosmic-ray muons and LED-based monitoring data. Cosmic-ray muons provide a clean source of minimum-ionizing particles in the absence of beam collisions and are used to study channel-to-channel response uniformity and signal stability. Because cosmic-ray muons traverse the full calorimeter and deposit clean minimum-ionizing signals, these measurements are well suited for studying response uniformity in both IHCal and OHCal.

In parallel, LED calibration data are used to investigate the temperature dependence of the SiPM response in both IHCal and OHCal. Signal amplitudes are extracted using waveform template fitting and correlated with measured temperatures to determine tower-by-tower correction factors. A clear linear dependence of the response on temperature is observed, and applying these corrections significantly reduces time-dependent gain variations.

The combined use of cosmic-ray and LED calibration techniques provides a robust and complementary approach for monitoring HCAL performance, ensuring a stable energy scale and reduced systematic uncertainties for sPHENIX physics analyses.

Speaker: Ahsan Mehmood Khan (University of Science and Technology of China (CN))

19:40 Calorimeter-Based Jet Shape Measurements in sPHENIX

Jet shape observables probe the internal structure of jets and are sensitive to differences between quark- and gluon-initiated radiation patterns, and thus they provide insight into the parton-to-jet fragmentation process. This poster presents a feasibility study of differential and integrated jet shapes in proton-proton collisions at a center-of-mass energy of 200 GeV, using calorimeter-reconstructed jets in the sPHENIX experiment at the Relativistic Heavy Ion Collider. Using Monte Carlo simulations, we assess the potential to perform these crucial tests of perturbative QCD and quantify non-perturbative effects in a detector environment without full particle tracking. The methodology developed in this study will be applied to sPHENIX proton-proton data collected in 2024.

Speaker: Aahana Brahma (Georgia State University)

19:40 Characterization of Jet Quenching via Machine Learning

Jets have been used as an indirect probe to study the properties of the quark gluon plasma (QGP). Machine learning (ML) models are a useful means for performing studies in general because they can learn complex patterns and relationships from data without requiring explicit analytic solutions. This is particularly useful when it is difficult to obtain solutions using traditional methods, as is the case with modeling of QGP related effects. To extend our understanding of the path length dependence of jet modifications, we developed techniques using ML optimized for making physically constrained predictions. This study uses experimentally measurable jet observables to predict jet quenching with extensions planned for parton flavor tagging and characterizing background. In this talk, we will present a score, the “Z-metric” which can provide levels of significance of these observables for predicting the amount of quenching experienced by the jet. Pythia, Jewel and Hydjet event generators are used in training samples to assess if the predictions made are model independent. This study utilizes a gradient boosted random forest model, although the presented metric can be applied to neural networks of various types. The model interpretability, made possible by the proposed Z-metric, allows for the isolation of different physics processes (soft radiation background, flow, energy transfer to generated QGP medium, dispersion in QGP medium) present in the measured observables by decoupling the input features, making this a promising tool for experimental analysis. These developments will be used to characterize jets in experimental data.

Speaker: Khovesh Anthony Ramdin (Rutgers State Univ. of New Jersey (US))

KRHP26.pdf

19:40 Characterizing inclusive charged-particle jet production and fragmentation in pp collisions with ALICE

Jets, collimated showers of particles originating from high-energy parton scatterings, are powerful probes of perturbative QCD. After an initial hard scatter, their evolution involves a perturbative shower followed by hadronization. As such, their internal structure provides sensitivity to the dynamics of QCD across a wide range of scales.

Using the upgraded Inner Tracking System (ITS2) and the continuous readout of the Time Projection Chamber (TPC) in Run 3, we present ALICE measurements of inclusive charged-particle jet production as a function of the jet resolution parameter R in proton-proton collisions at a center-of-mass energy of 13.6 TeV. The increased statistical reach enables improved precision, providing tighter constraints on perturbative QCD calculations for jet production.

Jet fragmentation is further characterized through measurements of the transverse momentum fraction $j_\rm T$ as a function of the longitudinal momentum fraction $z$ of jet constituents. These observables provide complementary information on the distribution of momentum within jets, resulting in a multi-dimensional and constraining picture of jet production and fragmentation.

Speaker: Joonsuk Bae (Sungkyunkwan University (KR))

JBae_HP2026_poster_6th.pdf

19:40 Characterizing QGP properties with Quarkonium beyond the Markovian limit

The in-medium dynamics of quarkonium, bound states of heavy quark-antiquark pairs, is one of the few examples of physical processes that can be studied in heavy ion collisions where a frequency-dependent two-point function of the quark-gluon plasma (QGP) degrees of freedom may be probed directly. Traditional phenomenological calculations make the Markovian assumption of no memory effect in the dynamics. Yet, there is evidence from recent calculations that Markovian physical processes may not be the dominant drivers of the dynamics in the strong coupling limit.

In this work, we initiate a study of in-medium quarkonium dynamics using an approach that fully captures the memory effects induced in quarkonium dynamics via QGP correlators, at the cost of treating the dynamics of unbound heavy quark pairs in an approximate but systematically improvable way. As such, our results provide a window to access novel QGP information from experimental data. Comparison with data will be presented.

Speakers: Bruno Scheihing (KITP, University of California, Santa Barbara), Xiaojun Yao (University of Washington)

Scheihing_Yao-Hard_Probes_2026_Poster.pdf

19:40 Charged-particle jet fragmentation in pp collisions with ALICE

Jet substructure observables based on final-state hadrons provide sensitive probes of parton-shower evolution and hadronisation. The ALICE Collaboration has measured the transverse momentum fraction, $j_{\mathrm{T}}$, of charged-jet constituents in pp and p--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02~\mathrm{TeV}$, both inclusively and differentially in the longitudinal momentum fraction, $z$. These results, together with comparisons to MC event generators, offer quantitative constraints on perturbative and non-perturbative QCD dynamics and serve as an essential baseline for future medium studies.

In this contribution, we present jet fragmentation results and discuss their implications for understanding both the perturbative shower and non-perturbative hadronisation components in the evolution of jets. We also present the status of a more differential fragmentation analysis, using the newly collected datasets from Run 3, where the substantial statisical gain, due to the upgrades to the ALICE detector, are leveraged. These results aim to extend the precision of the measurement and introduce new multiplicity-dependent studies to investigate possible medium-like effects in high-multiplicity pp collisions. These studies extend the quantitative understanding of jet fragmentation, from the interplay of perturbative and hadronisation dynamics to the search for possible modifications in various collision systems.

Speaker: Jaehyeok Ryu (Pusan National University (KR))

HP2026Poster_Jet_Jae_v3.pdf

19:40 Charged-particle jet production in OO collisions at $\sqrt{s_{\rm NN}} = 5.36$ TeV with ALICE

Jet quenching, the energy loss and modification of high-energy partons as they traverse a hot and dense medium, serves as a probe of the properties of the Quark-Gluon Plasma (QGP). While jet quenching has been observed in large systems, OO collisions provide an intermediate system, bridging the gap between pp and Pb-Pb collisions. This allows quantitative studies of the onset of jet quenching effects and its dependence on system size. In this poster, we present studies of jet reconstruction performance and background subtraction in OO collisions at $\sqrt{s_{\rm NN}}$ = 5.36 TeV. These studies constitute an essential step towards the measurement of the nuclear modification factor of inclusive jets in OO collisions, aiming at establishing potential jet-quenching signals in light-ion collisions.

Speaker: Wooseok Ham (Sungkyunkwan University (KR))

2026HardProbes_poster_WooseokHam_final.pdf

19:40 Charmonia at Finite Momentum and Spatial Correlators in Quark-Gluon Plasma

Spatial correlation functions of quarkonia in the quark-gluon plasma are available from finite-temperature lattice-QCD with good precision. However, their interpretation in terms of microscopic spectral functions has been challenging due to numerical oscillations in the Fourier transform and the requirement of a reliable 3-momentum dependence. Utilizing the thermodynamic T-matrix, we first employ a separable-potential to establish a Lorentz-covariant scattering equation in vacuum. Medium effects are then included through state-of-the-art heavy-quark selfenergies, a zero-mode contribution derived from finite-temperature field theory, and a potential screening constrained by euclidean correlators at vanishing momentum. The resulting predictions for the 3-momentum quarkonium spectral functions can qualitatively reproduce the increase of euclidean correlators with 3-momentum, as well as the suppression the spatial correlator ratios, as found in lattice QCD.

Speaker: Thomas Hardin

Charmonia at Finite Momentum and Spatial Correlators in Quark-Gluon Plasma Poster.pdf

19:40 Charmonium production in Pb–-Pb collisions at forward rapidity with ALICE

Quarkonium production in high-energy heavy-ion collisions is a key tool to study the production and the properties of the quark-gluon plasma (QGP), a state of matter in which quarks and gluons are no longer confined inside hadrons.

Charmonia are quarkonium bound states consisting of a charm and an anti-charm quark.
Charmonium production in Pb--Pb collisions is sensitive to the quark–gluon plasma through color-screening–induced suppression and regeneration from uncorrelated $\mathrm{c}\bar{\mathrm{c}}$ pairs, whose interplay depends on the medium properties and on the quarkonium binding energy. A comparative study of J/$\psi$ and $\psi$(2S) production provides a powerful probe of these effects: the more weakly bound $\psi$(2S) is expected to be more strongly suppressed, while regeneration is predicted to play a significant role at LHC energies, making the relative production of the two states especially sensitive to the medium evolution and challenging for theoretical models. In this poster, I will present the analysis status of inclusive J/$\psi$ and $\psi$(2S) production at forward rapidity (2.5 $< y <$ 4) in Pb–-Pb collisions at a center-of-mass energy per nucleon pair of $\sqrt{s_{\mathrm{NN}}} = 5.36$ TeV. The analysis is based on the data collected in 2023 and 2024 by the upgraded ALICE detector during LHC Run 3, which provide a larger data sample compared to previous data-taking periods. The double ratio of $\psi$(2S) to J/$\psi$ yields in Pb–-Pb and pp collisions, the J/$\psi$ and $\psi$(2S) nuclear modification factor $R_{AA}$ will also be reported. The results will be compared to similar measurements from data collected during LHC Run 2, and with theoretical models.

Speaker: Sara Garetti (Université Paris-Saclay (FR))

19:40 Cold Nuclear Matter Effects: An unsolved puzzle

This contribution presents a review of cold nuclear matter (CNM) effects in hadron–nucleus collisions, with a focus on hard probes such as Drell–Yan pairs, heavy flavor, and quarkonium production. By examining yield modifications as functions of transverse momentum and rapidity, these studies aim to disentangle key QCD mechanisms, including gluon saturation, nuclear PDFs, and parton energy loss, and to determine whether observed suppression patterns reflect universal features or process-dependent effects.
The future Electron–Ion Collider (EIC) at Brookhaven National Laboratory, together with its ePIC detector, will provide an unprecedented opportunity to explore these questions with high precision. Beyond its primary collider mission, the EIC should also be considered as a multi-purpose facility for the coming decades of nuclear physics, with the flexibility to support complementary modes of operation that broaden its scientific reach.

In this context, the potential of operating the EIC in a fixed-target mode is proposed [1]. Such a program would enable proton–nucleus and ion–nucleus collisions at low center-of-mass energies, complementary to the STAR fixed-target program and to the upcoming CBM experiment at FAIR. As discussed at the recent fixed-target workshop [2], this mode would significantly broaden the horizons of QCD studies at the EIC by covering a wide range of beam energies and target nuclei.

A fixed-target program at the EIC would also extend the capabilities of ePIC toward heavy-quark and quarkonium production at higher Bjorken-x, offering a unique opportunity to disentangle cold nuclear matter effects in this energy regime. Together, these studies provide a roadmap for interpreting future nuclear data and for using the EIC not only as a collider, but as a versatile facility to deepen our understanding of QCD in nuclear environments.

[1] F. Arleo, P. Caucal, A. Deshpande, J. M. Durham, G. M. Innocenti, J. Jalilian-Marian, A. Kusina, M. X. Liu, Y. Mehtar-Tani, C. J. Naïm, H. Paukkunen, S. Platchkov, F. Salazar, I. Vitev, and R. Vogt, “Nuclear Cold QCD: Review and Future Strategy,” arXiv:2506.17454, 2025.

[2] Exploring a Fixed-Target Program at the EIC, Center for Frontiers in Nuclear Science workshop, available at: https://indico.cfnssbu.physics.sunysb.edu/event/496/

The work of C.-J. Naïm is supported by the Center for Frontiers in Nuclear Science and the Simons Foundation. R. Vogt is supported by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, the LLNL-LDRD Program under Project No. 23-LW-036, and through the Topical Collaboration in Nuclear Theory on Heavy-Flavor Theory for QCD Matter under award no. DE-SC0023547.

Speaker: Ramona Vogt

HP2026_poster_v6.pdf

19:40 Collective effects in small systems in LHCb

In heavy-ion collisions, collective phenomena in the hot and dense medium known as the Quark–Gluon Plasma (QGP) are probed through measurements of mean transverse momentum and azimuthal particle correlations. Similar correlation patterns observed in small collision systems raise questions about their origin, involving either final-state collective effects or initial-state parton correlations. The LHCb experiment has unique capabilities to study these observables at forward rapidity in high-energy hadronic collisions, accessing a kinematic region not covered by other LHC detectors, where longitudinal dynamics are more pronounced. By comparing forward and backward pseudorapidity measurements, LHCb also gains sensitivity to initial-state effects. This contribution presents recent LHCb results on mean transverse momentum and collective flow, providing new constraints on the mechanisms driving particle correlations across collision systems.

Speaker: Elaina Hillary Saltclah (Los Alamos National Laboratory (US))

19:40 Covariant Jet Momentum Broadening in QCD Effective Kinetic Theory

Jets probe the quark–gluon plasma at its earliest, most far-from-equilibrium stages, when the medium is strongly flowing and highly anisotropic. Medium-induced broadening is typically encoded in a single scalar transport coefficient, the jet quenching parameter $\hat q$, defined in the medium’s local rest frame. This scalar description is tied to a specific local rest frame and a single “transverse” plane, missing the rich directional structure and flow-induced anisotropies that appear in broadening in realistic, flowing, anisotropic QCD matter.

We generalize $\hat q$ to a covariant rank-two tensor that emerges directly from first-principles QCD effective kinetic theory as the momentum-space diffusion tensor for a high-energy parton. This object simultaneously encodes transverse momentum broadening, energy diffusion, and energy–momentum correlations, and obeys general model-independent positivity (“diffusion”) constraints analogous to energy conditions for the stress tensor. We compute the full tensor structure and its non-equilibrium corrections within QCD effective kinetic theory and discuss how our framework can be implemented in phenomenological jet-quenching simulations of flowing, out-of-equilibrium quark–gluon plasmas relevant for heavy-ion collisions.

Speaker: Ms Isabella Danhoni

poster_hp.pdf

19:40 Deterministic AI Surrogate Modeling for Fast Hydrodynamic Evolution of the Quark Gluon Plasma

Accurate modeling of the space–time evolution of the quark–gluon plasma (QGP) through relativistic hydrodynamics is essential for connecting initial-state fluctuations to final-state observables and for understanding interactions between hard probes and the evolving QGP in heavy-ion collisions. However, full hydrodynamic simulations are computationally intensive, posing major challenges for large-scale parameter scans and event-by-event analyses. A typical 2+1D simulation requires about an hour per event on CPU, while a 3+1D evolution for central Pb+Pb collisions can take up to ten hours per event, making comprehensive studies prohibitively expensive. We introduce a deterministic AI–based surrogate model that emulates the full QGP hydrodynamic evolution with unprecedented speed. Trained on viscous hydrodynamic solutions from MUSIC, the model achieves orders-of-magnitude faster inference while maintaining high fidelity to the underlying dynamics. This dramatic reduction in computational cost transforms the feasibility of QGP evolution studies, enabling fast and accurate access to full time-dependent information and paving the way for precision, high-statistics analyses.

Speaker: Yeonju Go (Brookhaven National Laboratory (US))

20260621_HP2026_TCQGP_YeonjuGo.pdf

19:40 Deuteron identification and production at LHCb

This contribution presents an innovative method for deuteron identification at LHCb. By exploiting time-of-flight measurements from the gaseous tracker located downstream of the LHCb magnet, distinct nuclear species, from deuterons to alpha particles, are clearly observed in fixed-target $pHe$ collisions, achieved via helium injection into the LHC beam pipe using the SMOG system. This technique opens new possibilities for a rich program of measurements with relevance for both QCD and astrophysics.

Speaker: Nicholas William Retan (Los Alamos National Laboratory (US))

19:40 Dielectron analysis in Pb$-$Pb collisions in Run 3 with ALICE

Correlated electron-positron pairs (dielectrons) are a unique probe for studying the properties of the medium created in relativistic heavy-ion collisions. They are produced at all stages of the collision and leave the system without loss of information, as they do not interact strongly with the medium. However, at LHC energies, thermal dielectrons emitted in the early stages of the collision from the quark-gluon plasma are outnumbered by a large contribution of correlated e$^{+}$e$^{-}$-pairs from semi-leptonic decays of heavy-flavor (HF) hadrons.

With the upgrade of the ALICE detector for LHC Run 3, the sensitivity to thermal dielectrons is improved. Continuous readout of the TPC allows for a higher data acquisition rate of up to 50 kHz in Pb$-$Pb collisions. Moreover, the new ITS with its higher granularity and closer proximity to the interaction point improves the pointing resolution, leading to a better topological separation of prompt thermal radiation and non-prompt e$^{+}$e$^{-}$ pairs from HF hadron decays.

This poster presents the analysis of dielectron production in Pb$-$Pb collisions at $\sqrt{s_{\rm{NN}}}=5.36$ TeV, recorded with the upgraded ALICE detector in Run 3. The distance of closest approach (DCA) of the electrons to the primary vertex of the collision will be investigated, and the impact of the detector upgrades on the dielectron analysis will be shown.

Speaker: Emma Charlotte Ege (Goethe University Frankfurt (DE))

HP26_poster_EmmaEge.pdf

19:40 Differential probes of jet evolution with charged energy-energy correlators at ALICE

Energy-energy correlators (EECs) are energy-weighted cross-sections of particle pairs. They reflect QCD dynamics across the full scales of jet evolution by separating energy scales in the jet fragmentation through the angular distance of the particle pairs in the jet. Charged EECs probe the energy flux carried by pairs with the same or opposite electric charges. The interplay between energy distribution and charge conservation enables charged EECs to provide novel constraints on hadronization mechanisms. We present measurements of two-point charged EECs for charged-particle jets in pp collisions at $\sqrt{s} = 5.02$ TeV using the ALICE detector, and compare them to models employing different parton shower and hadronization prescriptions. We also present measurements in p-Pb collisions, examining cold nuclear matter effects on jet dynamics.

Speakers: Tucker Hwang (University of California Berkeley (US)), Tucker Hwang

charged_EEC_poster_HP26.pdf

19:40 Dijet momentum imbalance and azimuthal correlations in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV with the sPHENIX detector

Measurements of dijet kinematic correlations in heavy ion collisions provide insight into the mechanisms of jet quenching by the quark-gluon plasma. The sensitivity to medium-induced modifications such as dijet $p_T$ asymmetries and angular decorrelations is expected to be enhanced at RHIC, due to the tighter initial kinematic correlations, compared to those at the LHC. This presentation details measurements of dijet momentum imbalance $x_J$ and azimuthal correlations $\Delta\phi$ in Au+Au collisions at $\sqrt{s_{_{NN}}} = 200$ GeV using the sPHENIX calorimeter system, including the subtraction of the underlying event and corrections for contributions from a flow-modulated combinatorial background to dijet azimuthal correlations. The results for anti-$k_{t}$ $R=0.3$ jets are fully unfolded for detector effects and compared between Au+Au and $p$+$p$ collisions. The experimental data are also compared with jet quenching theoretical and Monte Carlo calculations.

Speaker: Dr Tanner Mengel (University of Colorado, Boulder)

tmengel_hp2026_poster_v2.pdf

19:40 Dijet production in intermediate x at EIC

The contribution of photon-gluon fusion to dijet production in deeply inelastic scattering is typically analyzed in the small-x regime, whereas photon-quark scattering dominates at large x. The transition between these regimes has received less attention. In this work, we calculate the leading-order and twist-four photon-gluon fusion contribution within a generalized high-twist framework for the intermediate-x region (0.001 < x < 0.1). Comparison with photon-quark scattering shows the photon-gluon channel grows as x decreases, becoming dominant for x < 0.1. These results bridge dijet dynamics across x, connecting large-x LPM effects with small-x saturation phenomena, thereby informing the development of event generators for deeply inelastic scattering at electron-ion colliders.

Speakers: Dr Xin-Nian Wang (Lawrence Berkeley National Lab. (US)), Yu Fu (Duke university)

main.pdf

19:40 Dynamical soft--hard hadron correlations across momentum scales in the quark--gluon plasma

The dynamical correlation of collective modes and jet quenching is a key open problem in the study of the quark-gluon plasma (QGP). In this contribution we propose a new analysis framework (arXiv: 2512.10265) for exploring dynamical soft--hard correlations in heavy--ion collisions, based on the $p_T$-differential radial-flow observable $v_0(p_T)$ that correlates different components of the inclusive hadron spectrum. We show that the characteristic rise--plateau--downturn structure and species hierarchy in $v_0(p_T)$ that has been reported at the LHC arises from a controlled sequence of coherent soft fluctuations, partially coherent coalescence dynamics, and decorrelated or anti-correlated hard-sector fluctuations. We introduce an experimentally measurable reference-aligned covariance matrix $V_0(p_{T1},p_{T2})$ to quantify this evolution. The subleading-to-leading eigenvalue ratio $\lambda_2/\lambda_1$ of $V_0(p_{T1},p_{T2})$ measures the effective fluctuation rank, while the $p_T$ dependence of the corresponding eigenvectors reveals how additional fluctuation modes emerge as mid- and high-$p_T$ dynamics become active. Together with the factorization ratio $r(p_{T1},p_{T2})$, these observables directly probe the soft--hard correlation topology in an experimentally accessible way, providing sensitive probes of the coupling between high-$p_T$ hadron production dynamics and the fluctuating QGP medium. We discuss their application to existing and forthcoming RHIC and LHC data, which will provide new constraints on jet--medium interaction mechanisms.

Speaker: Lipei Du (UC Berkeley / LBNL)

HP26-LDU.pdf

19:40 Electron reconstruction in p+p collisions using sPHENIX silicon trackers and calorimeters

The sPHENIX collaboration accumulated 75 $pb^{-1}$ of p+p data in 2024 during the TPC commissioning period. We are developing a novel track reconstruction method based on high-precision silicon vertexing detectors and calorimeters with the goal of pursuing measurements of $J/\psi$ production through its di-electron decay channel using the TPC commissioning dataset.
In this poster, we describe the track reconstruction method under development and report the current status of analyses using p–p collision data and simulations.

Speaker: Takashi Hachiya (Nara Women's University (JP))

HP2026_poster_hachiya_eID_v2.pdf

19:40 Electron–muon azimuthal correlations from heavy-flavor hadron decays in proton-proton collisions at √s=13.6 TeV with ALICE

Heavy-flavor production measurements in proton‒proton (pp) collisions offer stringent tests of perturbative quantum chromodynamics (pQCD) calculations and serve as an essential baseline for heavy-ion collisions studies. Azimuthal correlations of lepton pairs from heavy-flavor hadron decays are sensitive to heavyflavor production mechanisms and, ins heavy-ion collisions, to in-medium energy loss effects. In this work, we focus on a particularly clean channel: electron‒muon pairs from heavy-flavor hadron decays. This signature allows for a clean measurement by strongly suppressing backgrounds from electromagnetic processes such as Drell‒Yan production and resonance decays. The ALICE detector provides a unique capability for this study due to the large rapidity gap between the electron and muon detection regions. This feature suppresses near-side jet correlations and enables access to long-range correlations, offering new sensitivity to multiparton interactions and collective flows in small systems. We report the current status of the analysis of transverse-momentum‒inclusive azimuthal correlations of electron‒muon pairs from heavy-flavor hadron decays in pp collisions at √s = 13.6 TeV.

Speaker: Shunsuke Kurita (Hiroshima University (JP))

skurita_HP2026_poster_ver6.pdf

19:40 Exploring Muon Identification for Heavy Flavor Measurements in the sPHENIX Experiment

The science mission of sPHENIX is to make precision measurements of heavy flavor,
quarkonia, and jets to quantitatively determine the transport properties and micro-
scopic structure of the quark–gluon plasma created at RHIC. Muon identification in
sPHENIX provides a clean, complementary probe to traditional heavy-flavor identifica-
tion methods, such as secondary vertex tagging and electron identification, enabling en-
hanced sensitivity to bottom quarks, reduced hadronic backgrounds, and independent
constraints that strengthen the overall heavy-quark physics program. In this study,
muon–pion separation is evaluated using calorimeter information from the electromag-
netic calorimeter (EMCal), inner hadronic calorimeter (IHCal), and outer hadronic
calorimeter (OHCal) in sPHENIX. Several shower-related observables—including the
energy-to-momentum ratio, calorimeter energy fractions, tower multiplicity, and shower
dispersion—are combined into a log-likelihood ratio (LLR) discriminant to quantify the
probability that a track is muon-like or pion-like. The performance of the LLR-based
muon identification is assessed across a range of transverse momenta, and both the
muon efficiency and pion misidentification rates are reported. The results provide a
comprehensive characterization of calorimeter-based muon identification and establish
a foundation for robust particle-selection strategies in future analyses.

Speaker: Ghosoun Adawi (Georgia State University)

19:40 Exploring small-angle emissions in D0-tagged jets in Pb-Pb collisions at 5.02 TeV

The mass of heavy quarks modifies the pattern of QCD radiation inside jets by suppressing soft and collinear gluon emissions through the dead cone effect. In heavy-ion collisions, this mass-dependent effect provides a unique opportunity to probe the interplay between vacuum and medium-induced radiation. We present a Run 2 measurement of the substructure of charm-tagged jets in PbPb collisions at \sqrt{s_{NN}} = 5.02 TeV with the CMS detector. Jet substructure techniques based on the reconstruction of an angle-ordered branching history are used to access the dead cone region and to isolate hard splittings inside the jet. By comparing the angular structure of D0-tagged jets to inclusive jets, in pp and PbPb collisions, the sensitivity to charm quark mass effects in the presence of the quark–gluon plasma is investigated. Comparisons to models and calculations are discussed.

Speaker: Lorenzo Frosina (Sapienza Universita e INFN, Roma I (IT))

19:40 Extraction of Fragmentation Function of Photons using JetScape

Jets and their QCD emissions are an important topic for the study of parton evolution in the QGP. Quark jets can radiate photons during their parton shower process and so far, these fragmentation photons have remained unexplored during the study of Heavy-ion Collisions. These photons will allow us to explore the EM component of the parton shower in the presence of a medium, which is currently less developed. This research utilizes the JETSCAPE framework to analyze photons found within jets, labeling them as fragmentation photons, and obtain their momentum fraction (z=pTγ/pT,jet) and angular relationship (ΔR) to the jet axis. The primary objective is to examine jet quenching by characterizing the modified photon fragmentation function and jet shape in simulations of AuAu at 200 GeV center-of-mass energy (RHIC energy) using these observables. The results of these simulations demonstrate an intriguing trend: as jet transverse momentum increases, fragmentation photons exhibit a higher momentum fraction compared to charged pions, and the physical implications of this remain to be seen. These findings facilitate the extraction of modified fragmentation functions, with potential applications on sPHENIX data collected in Run2025.

Speaker: McKenna Sleeth (Vanderbilt University)

Sleeth_M_HP_Poster2026.pdf

19:40 Femtoscopy measurements at LHCb

Femtoscopic techniques provide unique insight into particle production mechanisms in hadronic collisions and into the interactions between short-lived hadrons. These measurements offer an indirect approach to hadron spectroscopy by constraining hadron–hadron interactions and possible bound or resonant states. The excellent momentum resolution of the LHCb detector makes it well suited for femtoscopic correlation studies. In addition, its vertex reconstruction and particle identification capabilities enable measurements involving both light and heavy hadrons. Recent results on femtoscopic correlations of light and heavy hadrons will be presented.

Speaker: Jackson Reeves Pybus (Los Alamos National Laboratory (US))

19:40 Forward $\phi$-meson measurement in small and large systems at $\sqrt{s_{\rm NN}}$=200 GeV by PHENIX

The $\phi$ meson serves as a key probe for studying the quark-gluon plasma (QGP) due to its short lifetime and the weak interaction of its decay muons with the surrounding hadronic matter, making the $\phi\rightarrow \mu^+\mu^-$ decay channel particularly effective. As a pure $s\bar{s}$ state, the $\phi$ meson provides insight into strangeness enhancement and the mechanisms governing parton interactions in the QGP, placing strong constraints on models of parton energy loss and recombination. Previous PHENIX measurements in small collision systems revealed cold nuclear matter effects on $\phi$ meson production. Extending these studies to Au+Au collisions allows exploration of hot nuclear matter effects, including modification of parton dynamics and hadronization in the QGP. In this talk, we present the first measurement of low-mass vector mesons ($\omega$, $\rho$, and $\phi$) at forward rapidity ($1.2 < |y| < 2.2$) in $p$+$p$ and Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV, using the PHENIX detector. Results are reported as a function of transverse momentum ($p_T$) and the average number of participating nucleons, $\langle N_{part}\rangle$. While $\omega$ and $\rho$ mesons show significant suppression across the full $p_T$ and $\langle N_{part}\rangle$ range, the $\phi$ meson exhibits a distinct pattern: suppression at high $p_T$ and enhancement in central collisions at intermediate $p_T$ region. These findings provide insight into the nuclear medium's effect on particle production and the flavor dependence of particle production in the QGP.\

Speaker: Murad Sarsour

19:40 From Lead to Helium: Discovery Potential for Jet Quenching in the Smallest Collision Systems

We present the first perturbative quantum chromodynamics (pQCD) predictions for modifications to high-momentum particle yields in very light ion collisions—${}^{10}\mathrm{B}+{}^{10}\mathrm{B}$, ${}^{6}\mathrm{Li}+{}^{6}\mathrm{Li}$, ${}^{4}\mathrm{He}+{}^{4}\mathrm{He}$, and ${}^{3}\mathrm{He}+{}^{3}\mathrm{He}$—with and without medium-induced energy loss. We find that our energy loss framework predicts a simple approximate system-size dependence, $R_{AB} \sim (\sqrt{AB})^{1/3}$, for both symmetric and asymmetric $A+B$ systems, with measurable suppression persisting down to ${}^{3}\mathrm{He}+{}^{3}\mathrm{He}$ collisions. The framework incorporates small-system-size corrections, quantifies theoretical uncertainties, and is constrained by a broad set of high-$p_T$ data in large systems, yielding predictions for recently measured oxygen and neon collisions that are in good agreement with preliminary data. We compare these energy loss predictions to baseline next-to-leading-order pQCD calculations including nuclear parton distribution functions to estimate the discovery potential for final-state partonic energy loss in very light-ion collisions. Owing to tightly constrained nuclear parton distribution functions, we find that ${}^{3}\mathrm{He}$ and ${}^{6}\mathrm{Li}$ are especially clean environments for isolating partonic energy loss. These results will inform the physics case for future light-ion runs at LHC.

Speaker: Coleridge Faraday (University of Cape Town)

HP2026 poster.pdf

19:40 Generalized background subtraction of N-point energy correlator in Heavy Ion Collisions

N-point energy correlators serve as a probe for the dynamics of the Quark-Gluon Plasma (QGP) by providing a map of the final-state particle energy flow. The measurement of jet substructure for low energy jets is complicated due to the impact of the underlying event. In this talk, we present a phenomenological study using Monte Carlo simulations focusing on the Whole Event Energy Correlator (wEEC) and the standard Energy-Energy Correlator (EEC) at RHIC energies. Our simulation environment utilizes PYTHIA paired with a hydrodynamic background from JETSCAPE to mimic the complexity of the heavy-ion environment. We analyze the effectiveness and necessary optimizations for background subtraction and reconstruction techniques, specifically focusing on identifying and mitigating reconstruction biases in EEC measurements. We discuss how these simulations inform our background subtraction strategy and offer insights into the overall sensitivity of EECs to jet modifications. This work helps in establishing the necessary methodological foundation for future experimental EEC measurements in heavy-ion collisions for low energy jets.

Speaker: Laurynette Griffin

FInal Hard Probes 2026 Poster - Laurynette Griffin-2.pdf

19:40 Groomed vs ungroomed jet angularities from \sqrt{s} = 200 GeV p + p collisions in STAR

Within jets originating from initial stages of hadron collisions, angular scales have been shown correlated with temporal and energy scales, giving insights into jet evolution from perturbative to non-perturbative quantum chromodynamic (p/npQCD) regimes. Contributions from pQCD interactions to jet substructure are isolated by grooming techniques, which minimizes npQCD effects by removing soft, wide-angle radiation from the jets. In presence of quark-gluon plasma (QGP), comparing angular distributions of both groomed and ungroomed jet constituents to a (p+p) baseline reveal signatures of jet quenching in QGP, like broadening.

Generalized jet angularities, defined as $\Lambda^\kappa_\beta = \sum_{i\in\mathrm{jet}}\left(\frac{p_{\mathrm{T}, i}}{p_{\rm T, jet}}\right)^\kappa \left(\frac{\Delta R}{R_0}\right)^\beta$ [1], are jet substructure observables characterized by exponents $\kappa$ and $\beta$ which tune dependence on transverse momentum fraction $\left(\frac{p_{\mathrm{T}, i}}{p_{\rm T, jet}}\right)$ and rapidity/azimuth angle $\Delta R$, scaled by jet-resolution parameter $R_0$ from the jet-axis respectively, varying sensitivity of the observable to collinear and soft radiation. Measurements at RHIC energy scales complement previous LHC results [2] by studying the impact of grooming on jet substructure in regions of the phase-space unexplored by LHC. As theoretical calculations need to capture the full spectrum of pQCD and npQCD processes to explain jet evolution in vacuum and medium, these results will provide useful constraints.

In this study, we present measurements of various angularities using jets from (p + p) collisions at $\sqrt{s}$ = 200 GeV, collected by the STAR experiment. The measurements are fully corrected for detector effects using MultiFold [3], featuring various improvements to the unbinned unfolding method. Measurements from inclusive jets are compared with those from their SoftDrop-groomed counterparts. Finally, the data are compared with model calculations and the physics implications are discussed.

[1] Larkoski, A., Thaler, J. & Waalewijn, W. Gaining (mutual) information about quark/gluon discrimination. Journal Of High Energy Physics 2014 (2014,11), http://dx.doi.org/10.1007/JHEP11(2014)129

[2] Acharya, S. & Others, Measurements of the groomed and ungroomed jet angularities in pp collisions at $\sqrt{s}$ = 5.02 TeV. JHEP 05 pp.061 (2022)

[3] Andreassen, A., Komiske, P., Metodiev, E., Nachman, B. & Thaler, J. OmniFold: A Method to Simultaneously Unfold All Observables. Physical Review Letters. 124 (2020,5), http://dx.doi.org/10.1103/PhysRevLett.124.182001

Speaker: Tanmay Pani (Rutgers University)

poster.pdf

19:40 Hadronization in heavy-flavour jets at LHCb

Jets produced in conjunction with heavy hadrons provide unique probes of the nonperturbative hadronization process. Heavy-flavor jets can be used to study the hadronization of heavy quarks into heavy-flavor hadrons. In addition, they can reveal how light hadrons are produced during heavy quark hadronization. These studies can be used to constrain the fragmentation functions that are used to parameterize the hadronization process. This talk presents recent studies of hadronization in heavy-flavor jets in pp collisions with the LHCb detector. These studies include measurements of hadronization to light- and heavy-flavor hadrons.

Speaker: Ezra Lesser (Los Alamos National Laboratory)

EzraLesser_Hadronization_in_HF_jets_LHCb_HP2026.pdf

19:40 Heavy Quark dynamics in QGP using effective field theory

Heavy quarks are invaluable in probing the bulk properties of the medium. Unfortunately, the interactions between heavy quarks and the light degrees of freedom of the medium are not amenable to a description in terms of perturbative calculations. To remedy this situation, we develop a framework (arXiv: 2510.13942) based on effective field theory to understand the interaction of the heavy quark with the weakly coupled, collective degrees of freedom of the medium. In this theory the medium is treated as a colorless fluid and described by a derivatively coupled scalar theory. The interaction between the heavy quark and the fluid field then can be written down systematically using symmetries and power counting of the theory. We calculate the thermal scattering cross section between the heavy quark and the phonons, acting as collective excitations of the fluid fields. Additionally, we examine the decay width of a heavy quark-phonon resonance.

Speaker: Jyotirmoy Roy

Hard_Probes26.pdf

19:40 Heavy-flavour hadronization studies in small systems at LHCb

Heavy-flavor production studies at LHCb provide precise probes of hadronization in collision systems ranging from $\gamma$Pb interactions to semi-central PbPb collisions. Studies of heavy baryons and mesons containing two different heavy or strange valence quarks probe the interplay of statistical hadronization, coalescence, and multi-parton interactions. LHCb has capabilities to probe the full spectrum of open charm and beauty hadrons, including $\Lambda_c$, $\Xi_c$ and $B_c$, thanks to its precise vertexing, momentum resolution and particle identification capabilities. In this contribution, new results on open heavy-flavor and strangeness production from the LHCb experiment will be presented, providing new constraints on hadronization dynamics and nuclear effects in small systems.

Speaker: John Matthew Durham (Los Alamos National Laboratory)

Durham_hadronization_poster.pdf

Durham_upsilon_poster_vertical.pdf

19:40 High-$p_T$ $R_{AB},v_2,v_3$ and $v_4$ from Energy Loss in pPb, dAu, OO, and NeNe

We present predictions from a pQCD-based energy-loss formalism for the leading high-$p_T$ hadron observables $R_{AB}, v_2,v_3$ and $v_4$ in the small systems of pPb, dAu, OO, and NeNe. The energy-loss model is particularly well suited for the study of small systems as the formalism incorporates event-by-event hydrodynamic evolution of the medium's scattering centers, includes short path-length corrections, and consistently enforces the large formation-time approximation. The model's parameters are constrained to large-system $R_{AA}$ and $v_n$ data from RHIC and the LHC; we find that the extracted values of $\alpha_s\approx0.27$ and $\hat{q}/T^3\approx5.5$ can simultaneously describe high-$p_T$ $R_{AA},v_2$, and $v_4$ data, although a significant tension arises in the description of high-$p_T$ $v_3$. From the constrained model, we make the novel prediction that the high-pT charged hadron $R_{AB}$ is less than unity, but for all centrality classes there is no measurable $v_{2}\{SP\}$ anisotropy in pPb, dAu, OO, and NeNe collision systems; the lack of anisotropy arises as the orientation of the participant plane defined by hard particles and the participant plane defined by soft particles becomes decorrelated in these small systems.

Speaker: William Horowitz (University of Cape Town)

19:40 Identifying Jet Quenching in Simulated Heavy-Ion Collisions with Machine Learning Models

The Monte Carlo event generator JEWEL (Jet Evolution With Energy Loss) provides a
theoretical framework to simulate parton energy loss in a dense QCD medium such as the
Quark–Gluon Plasma (QGP). Traditionally, comparisons between theory and experiment
rely on global observables, including the nuclear modification factor $R_{AA}$ and the
dijet momentum imbalance $x_J$. In this work, we take a different approach by adopting
a jet-by-jet analysis to identify quenched jets directly from the jet substructure with
supervised machine learning architectures.
For this purpose, we employ JEWEL with both the default configuration, which employs
Glauber initial conditions coupled to Bjorken hydrodynamic model, and a more realistic
medium description, combining T$ _ \mathrm{R}$ENTo initial conditions with the
(2+1)D hydrodynamic evolution of v-USPhydro.
Each jet is represented as a sequential trajectory along the Cambridge/Aachen
declustering tree, characterized by four substructure observables ($z$, $\Delta R$,
$k_\perp$, $m_{inv}$) at each splitting, which we analyze using two supervised machine
learning architectures: Long Short-Term Memory (LSTM) networks and Transformers.
Our results show that the machine learning models chosen in this work are excellent at
the binary classification problem of distinguishing quenched jets on a jet-by-jet basis,
with accuracies and AUC scores greater than 95\%. In addition, the trained models are
sensitive to medium properties that are hidden in traditional global observables,
demonstrating the potential of ML for probing the Quark-Gluon Plasma.

Speaker: Leonardo Lima Da Silva (Universidade de Sao Paulo (USP) (BR))

LeonardoLima_HP2026.pdf

19:40 Impact of the thermal photon rate uncertainty on the direct photon puzzle

Heavy-ion collisions produce a significant excess of low-$p_T$ direct photons that have a large $v_2$. Whether this strong direct photon signal can be explained by thermal photons radiated by the plasma depends critically on the value of the thermal photon emission rate. Building on published rate calculations from hadronic models, lattice QCD, perturbative QCD and holography, we systematically quantify the uncertainty of the photon rate as a function of the plasma's temperature and the photon's energy. Propagating these uncertainties to the photon spectrum and $v_n$'s using hydrodynamic simulations, we assess the impact on the photon puzzle under both optimistic and conservative uncertainty scenarios. We put forward a general framework that can update the rate's uncertainty using future calculations from lattice or other sources.

Speaker: Mr Harvir Dhindsa (Vanderbilt University)

HP2026Poster_Harvir.pdf

19:40 Inclusive and Dijet EEC measurements in proton-proton collisions with ALICE

Energy-energy correlators (EECs), defined as energy-weighted two-particle correlations within jets as a function of angular separation, have emerged as powerful probes of jet substructure across multiple QCD scales. In vacuum, EECs exhibit a clear separation between perturbative dynamics at large angles and non-perturbative physics at small angles. In heavy-ion collisions, jets traversing the quark-gluon plasma (QGP) undergo medium-induced modifications that alter their internal structure, making EECs sensitive probes of jet-medium interactions. In particualr, the path-length dependence of energy loss can be directly investigated using the assymtries in dijet systems.

The poster presents studies of inclusive and dijet EECs in proton–proton collisions using PYTHIA8 simulations and ALICE Run 3 data. The inclusive EEC establishes a precision baseline for understanding parton fragmentation in vacuum, using the significantly improved Run 3 statisitics to extend the kinematic reach of measurements to higher jet transverse momentum. In dijets, measuring the EECs seperately for the leading and subleading jet, as a function of the dijet momentum assymetry, provide additional insight on how the transition from perturbative to non-perturbative regimes depends on the interplay of the initial parton virtualities and the quenched jet momentum scale. These measurements provide the essential pp reference for quantifying QGP-induced modifications in future Pb-Pb measurements.

Speaker: Ibrahim Abualrob (University of Houston (US))

Ibrahim_finaldraft.pdf

19:40 Inclusive J/psi production at midrapidity in pp collisions at \sqrt(s) = 5.36 TeV with ALICE in Run3

Charmonia are bound states formed by a charm quark and its antiquark (𝑐𝑐¯). The creation of the heavy charm–anticharm pair results from hard partonic scattering that can be described within perturbative QCD, whereas the subsequent hadronization into a bound state is governed by non-perturbative QCD dynamics. Therefore, the study of charmonium production provides a key probe of both perturbative and non-perturbative aspects of QCD, helping to validate and constrain their theoretical descriptions. In relativistic heavy-ion collisions, charmonium production serves as an important probe of the hot and dense medium known as the quark–gluon plasma (QGP), providing valuable insights into its properties through the interaction with the medium. Thus, this measurement not only provides a stringent test of theoretical predictions at the new LHC energy but also establishes an essential baseline for future studies in larger collision systems such as OO, Ne–Ne, and Pb–Pb.

In this work, we present the inclusive J/𝜓 production at midrapidity (|𝑦|<0.9) via the dielectron decay channel in pp collisions at 𝑠√=5.36TeV, using Run 3 data collected with the ALICE detector.

Speaker: Hyungjun Lee (Sungkyunkwan University (KR))

19:40 Integrating Rivet into Bayesian parameter estimation

Bayesian inference efficiently explores high-dimensional theoretical parameter spaces with direct comparisons to experimental data. We present progress towards an analysis framework integrating established tools to enable reproducible, precision calibration of theoretical models in order to ease these comparisons. We use the Rivet toolkit to evaluate theoretical predictions at design points across parameter space, ensuring direct comparability with published experimental measurements. These comparisons provide training data for Gaussian process emulators built with surmise (from the BAND framework), enabling rapid interpolation across the full parameter space. The emulators are then incorporated into Bayesian calibration workflows using the bilby inference library, facilitating robust parameter estimation and uncertainty quantification. We demonstrate the framework's capabilities using PYTHIA 8 for proton-proton collisions, validating both functionality and computational performance. We compare our results to the Detroit Tune. The modular design enables straightforward extension to heavy-ion collision models, additional observables, and alternative theoretical frameworks. This work establishes a flexible foundation for systematic Bayesian studies, with future applications targeting precision extraction of heavy-ion collision properties and the fundamental characteristics of nuclear matter under extreme conditions.

Speaker: Christal Martin (University of Tennessee, Knoxville)

19:40 Intermediate mass dilepton measurements with LHCb in Run 3

The measurement of prompt dilepton production at hadron colliders represents a key signature of the partonic structure of hadrons, quark-gluon plasma and of the preequilibrium. There exists no measurement at masses below 10~$\rm{GeV}/c$ and low transverse momentum at TeV collision energies due to the dominating background from semileptonic decays of charm and beauty hadrons. We present the prospects for low-mass Drell-Yan measurements with LHCb in Run 3 in the mass range between 2.9-60~$\rm{GeV}/c^2$ with lepton transverse momentum above 1$\rm{GeV}/c$ and for intermediate mass dilepton measurements in heavy-ion collisions in collider mode. We discuss earlier LHCb measurements in the high mass region and discuss Run 3 detector performance, highlighting the software trigger, vertex reconstruction and particle identification capabilities. In particular, we present SemiCharmTag, a tagging algorithm to retrieve unbiased properties of leptons from semileptonic decays of charm hadrons and to improve the signal-to-background ratio. The performance is shown based on full simulations of pp collisions in the dilepton mass range 2.9-5~$\rm{GeV}/c^2$.

Speaker: Thomas Boettcher (Indiana University (US))

19:40 Investigating nuclear shape via the Breit-Wheeler process in U+U UPCs at STAR

Dielectron production can occur in ultraperipheral heavy ion collisions (UPCs) via the Breit-Wheeler process, in which the quasi-real photons from the heavy ion-induced electromagnetic fields interact to produce a low transverse momentum dielectron pair. This production is sensitive to the charge radius and nuclear shape of the atomic nucleus sourcing the photons. By comparing the momentum dependence of the production cross sections in Au+Au and U+U to each other and to lowest-order quantum electrodynamics calculations, sensitivity to differences in nuclear shape and resulting field strength distributions can be studied.

We present experimental results for the dielectron production cross sections through the Breit-Wheeler process in U+U and Au+Au UPCs at $\sqrt{s_{NN}}$ = 193 and 200 GeV, respectively, at STAR at pair $p_{T} < 0.25$ GeV/c. We also present comparisons of these results with QED numerical calculations for the predicted cross sections, which allow new constraints on the charge radius and skin depth for the uranium nucleus.

Speaker: Nicholas Jindal (Ohio State University (US))

HP2026_v4.pdf

19:40 Jet azimuthal anisotropies in O+O and Ne+Ne collisions at $\sqrt{s_{\mathrm{NN}}}=5.36~\mathrm{TeV}$ with ATLAS

Light-ion collisions provide a controlled laboratory to test the path-length dependence of parton energy loss in a QCD medium whose transverse size is significantly smaller than in Pb+Pb, while maintaining high jet rates at the LHC. ATLAS recorded $\sim 8~\mathrm{nb}^{-1}$ of O+O and $\sim 1~\mathrm{nb}^{-1}$ of Ne+Ne data at $\sqrt{s_{\mathrm{NN}}}=5.36~\mathrm{TeV}$ in 2025. This poster presents measurements of jet azimuthal anisotropies in O+O and Ne+Ne collisions, targeting $v_2$ and $v_3$ (and higher harmonics where statistically accessible) as functions of event centrality and jet transverse momentum. The measurements will be compared between O+O and Ne+Ne, and to existing Pb+Pb results and theoretical calculations, to constrain the system-size and geometry dependence of jet quenching in light-ion collisions.

Speaker: Mina Savic (Univ. Illinois at Urbana Champaign (US))

ATLAS-CONF-2026-006-HP2026Poster-MSavic.pdf

19:40 Jet Energy Scale Calibration and Measurement of the Inclusive Jet Cross-Section in p+p Collisions at $\sqrt{s}=200\,\mathrm{GeV}$ with the sPHENIX Detector

The sPHENIX detector at RHIC sampled with jet triggers $107\,\mathrm{pb}^{-1}$ of p+p collisions at $\sqrt{s}=200\,\mathrm{GeV}$ during the 2024 run, providing the first mid-rapidity hadronic calorimetry at RHIC for direct measurements of neutral-hadron contributions to jet energy. This poster reports the measurement of the inclusive jet production cross section as a function of transverse momentum using jets reconstructed with the anti-$k_{\mathrm{T}}$ algorithm with distance parameters $R = 0.2$--$0.6$ in the kinematic range $|\eta|<0.7$ and $p_{\mathrm{T}} > 15\,\mathrm{GeV}$. The jet energy scale (JES) calibration corrects systematic shifts arising from the non-compensating calorimeter response using \textsc{pythia}~8 Monte Carlo simulations with GEANT4 detector response. The jet energy resolution (JER) characterizes the finite precision of the detector energy measurement. The measured cross section is corrected for background rejection and trigger efficiency, and unfolded to the particle level using iterative Bayesian unfolding to account for detector response effects and the energy smearing from finite jet energy resolution. The unfolded cross section establishes a precision baseline for jet suppression measurements in the upcoming sPHENIX Au+Au program.

Speaker: Hanpu Jiang (Columbia University)

19:40 Jet Modifications Across the QGP and Hadronic Phases in J-PHASE Generator with SUBA-Jet

We report on the development of a state-of-the-art framework, the J-PHASE Generator with SUBA-Jet, which simulates partons and hadrons originating from hard scattering together with the evolution of the QGP and the hadronic phase, including the mutual interactions between the jet and the bulk medium and hadrons. The construction of the time-like parton shower and medium-induced radiative energy loss has been presented in Ref. [1]. In this contribution, we:

• Introduce a complete LO calculation of collisional energy loss.
• Benchmark the framework against a variety of jet observables in and PbPb and $pp$ collisions at the LHC energies.
• Investigate modifications of the jet originating from both QGP and hadronic phases within the complete framework.

The J-PHASE Generator with SUBA-Jet incorporates PYTHIA for the jet initial state and hadronization, T$_{\rm R}$ENTo-3D for the medium initial state, vHLLE second-order hydrodynamics, SMASH-hadron-sampler for particlization, and SMASH for the evolution of the hadronic phase of both bulk and jet hadrons.

[1] Iurii Karpenko, Alexander Lind, Martin Rohrmoser, Joerg Aichelin, Pol-Bernard Gossiaux, JHEP 03 (2025) 057

Speaker: Josef Bobek (CTU FNSPE)

Josef_Bobek_poster_HP_26_A0.pdf

19:40 Jet Quenching and Fluctuations.

Calculations of jet quenching often estimate the fractional energy loss $$\epsilon$$ of jets using non-fluctuating mean-field theories, which are adequate for some applications but miss the effects of fluctuations. Previous studies have incorporated fluctuations by constructing a spectrum $$P(\epsilon)$$ using a Compound Poisson Distribution (CPD) built from independent, identical emissions. By construction, this approach generates an unphysical region with $$\epsilon>1$$, requiring ad hoc regulation, such as renormalizing the $$\epsilon<1$$ continuum or introducing a delta function at $$\epsilon=1$$. These approaches inevitably distort the expectation value $$\langle \epsilon \rangle$$.In this work, we introduce a new constrained CPD without artificial distortions to $$\langle \epsilon \rangle$$ as well as a modification of the Poisson convolution itself that preserves $$\epsilon \leq 1$$. This provides a physically consistent framework for incorporating Poissonian energy-loss fluctuations. We then explore the implications of energy loss fluctuations for jet quenching phenomenology and its coupling to jet drift (asymmetric transverse momentum broadening), showing that drift is particularly sensitive to fluctuations, with jets that lose more energy becoming more susceptible to drift. These results highlight the importance of constrained energy-loss fluctuations for jet tomography at intermediate energies.

Speaker: Umair Ahmad (New Mexico State university)

POSTER FOR HP BY UMAIR AHMAD.pdf

19:40 Large scale comparisons between data and models using Rivet

Systematic comparisons between experimental measurements and theoretical models are essential for validating and improving event generators. Such comparisons offer stringent tests of the underlying physics and its implementation. The RIVET framework enables these studies through standardized and reproducible analysis routines that are directly aligned with published experimental results. Using RIVET, we present a comprehensive comparison of PHENIX measurements of transverse energy production ($dE_T/d\eta$), charged-particle multiplicity ($dN/d\eta$), and invariant yields ($dN/dp_T$) at midrapidity with simulations from PYTHIA 8, AMPT, HIJING, and SMASH. The study spans both small collision systems ($d+Au$, $^3He+Au$) and large systems ($Cu+Cu$, $Cu+Au$, $Au+Au$, and $U+U$) at $\sqrt{s_{NN}} \sim 200$ GeV, as well as $Au+Au$ collisions over a broad range of beam energies ($\sqrt{s_{NN}} = 7.7--200$ GeV). While the models reproduce general trends in the data, significant discrepancies remain, particularly at low energies and in peripheral collisions, highlighting the need for improved descriptions of particle production.

Speaker: Christine Nattrass (University of Tennessee (US))

Rivet_ET (3).pdf

19:40 Letting the data speak for itself: Model-Agnostic Hadronization at the EIC using a new Event Generator

The impact of the cold nuclear medium on hadronization remains an open problem. We introduce an Event-Generator framework for the Electron-Ion Collider that couples hard scattering dynamics and soft final-state interactions through eHIJING and SMASH, respectively. To study hadronization, we use time dependent cross-sections. We adopt a model-agnostic and physics-constrained approach using Gaussian Processes to construct these time-dependent cross sections that models the gradual onset of hadronic interactions. We perform simulations across multiple beam energies and e+A collision systems and compute nuclear modification factors $R_{eA}$ of identified particles as functions of hadron momentum fraction $z_h$, transverse momentum $p_T$, and Bjorken-$x$. We find that $R_{eA}$ exhibits a non-negligible sensitivity to the hadronization dynamics within the nuclear medium.

Speaker: Jordi Salinas San Martin

HP2026_Poster_JordiSalinasSanMartin.pdf

19:40 Low-$p_\mathrm T$ direct-photon production and HBT correlations in heavy-ion collisions measured with ALICE

Measurements of direct-photon production in heavy-ion collisions allow for unique insight into the space–time evolution of the hot and dense medium. The absence of final-state interactions and the negligible in-medium path length of photons allows the measurement of photons produced in all stages of the collision. The measurement of photon Hanbury Brown–Twiss (HBT) correlations allows to determine the spatial-temporal characteristics of the emitting source.
In this talk, results on direct-photon production and direct-photon HBT correlations in Pb–Pb collisions at $\sqrt{s_{\text{NN}}} = 2.76$ TeV and $\sqrt{s_{\text{NN}}} = 5.02$ TeV will be presented. These include a precise measurement of the direct-photon excess ratio $R_\gamma$ down to low $p_\text{T}$, as well as the extracted direct-photon HBT correlation radii $R_\text{inv}$ and $R_\text{out}$. All measurements are compared to state-of-the-art theoretical calculations incorporating all relevant photon sources.
Furthermore, the current status of analyses based on LHC Run 3 data will be discussed. The enhanced statistics of these data, in comparison to those of LHC Run 2, offer a unique opportunity to investigate the three-dimensional direct-photon HBT correlation function for the first time.

Speaker: Joshua Leon Konig (Goethe University Frankfurt (DE))

Poster_Joshua_Koenig_HP26.pdf

19:40 Massively Scaling Up Jet Modification Analysis: Global Curated Data, Analysis Infrastructure, and Tools

The path toward a definitive characterization of the Quark-Gluon Plasma (QGP) requires a simultaneous, global analysis of all available jet modification data. The JETSCAPE Collaboration presents a landmark, curated dataset, the most comprehensive to date, that unifies the entirety of available jet and high transverse momentum hadron measurements from the LHC and RHIC programs into a common format. Consisting of over 90 observables and thousands of data points, this dataset represents a foundational effort to centralize experimental results for an unbiased global fit. To enable rigorous theory-to-data comparisons, we introduce a user-friendly and extensible Bayesian inference framework powered by a machine-learning-enhanced pipeline. This infrastructure enables the rigorous treatment of systematic uncertainties, specifically addressing the complex correlations of similar measurements within and across different experimental collaborations. We demonstrate the capabilities of this framework with a new global extraction of the jet transport coefficient, $\hat{q}$, including jet-substructure observables for the first time. This framework promises unprecedented constraints on $\hat{q}$ by incorporating all available data. It serves as a new benchmark for the field and establishes a common analysis infrastructure for future high-precision QGP studies, enabling the rigorous extraction of fundamental QCD parameters and transport coefficients across diverse theoretical frameworks.

Speaker: Jingyu Zhang (Vanderbilt University)

19:40 Measurement of $\psi$(2S) production at midrapidity in Pb--Pb Collisions at $\sqrt{s_{\rm NN}} = 5.36$ TeV with ALICE

Quarkonium is a sensitive probe of the quark–gluon plasma (QGP) created in ultra-relativistic heavy-ion collisions. In the QGP, color screening leads to the suppression of all charmonium states. However, the large charm production cross-section at LHC energies can also cause enhanced charmonium production at the phase boundary or (re-)generation throughout the QGP evolution. The interplay between suppression and (re-)generation mechanisms reflects the underlying charm-quark dynamics in the QGP and during hadronization. Studying the $\psi$(2S) is particularly interesting because of its weaker binding energy, larger spatial size, and smaller feed-down contribution compared to the J/$\psi$. Previous measurements have shown a stronger suppression of $\psi$(2S) relative to J/$\psi$ and are compatible with both statistical hadronization at the phase boundary as well as a model with continuous breakup and formation in the QGP. To clarify the situation, data at low transverse momentum and midrapidity are necessary. In this contribution, we present the first results of inclusive $\psi$(2S) production at midrapidity in Pb–Pb collisions at $\sqrt{s_{\rm NN}} = 5.36$ TeV with the ALICE detector, together with the corresponding J/$\psi$ measurements.

Speaker: Jinjoo Seo (Heidelberg University (DE))

HP2026_jj_ver3.pdf

19:40 Measurement of $\Xi_{\mathrm{c}}^{+}$-baryon production in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.36~\mathrm{TeV}$ with ALICE

The ALICE experiment is designed to study the quark--gluon plasma (QGP) created in ultrarelativistic heavy-ion collisions. Heavy quarks, like charm and beauty, are produced in primary hard-scattering processes in the early stages of the collisions, and they experience the full space--time evolution of the system. Thus, they are unique probes to study the properties of the QGP. In addition, the ALICE Collaboration has measured the $\Lambda^{+}_{\mathrm{c}}$-baryon production across different collision systems, including pp, p--Pb, and Pb--Pb collisions. These measurements provide valuable input to the study of charm-quark hadronization. Extending this investigation to charm strange baryons such as the $\Xi^{0,+}_{\mathrm{c}}$ offers additional insight into the hadronization mechanism. The larger data samples being collected during Run~3 at the LHC, together with the improved detector resolution as a result of the ALICE upgrade, allow precise measurements of charm–strange hadron production in Pb--Pb collisions.
In this contribution, the final results from the recent measurement of $\Xi_{\mathrm{c}}^{0}$-baryon production in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02~\mathrm{TeV}$ are presented. Furthermore, the status of the measurement of $\Xi_{\mathrm{c}}^{+}$-baryon production reconstruction via the hadronic decay channel $\Xi_{\mathrm{c}}^{+} \rightarrow \Xi^{-}\pi^{+}\pi^{+}$ in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.36~\mathrm{TeV}$ is reported.

Speaker: Giyeong Kim (Inha University (KR))

Giyeong_Xic_PbPb_HP_ver4.1.pdf

19:40 Measurement of $\Xi_{\mathrm{c}}^{+}$-baryon production via hadronic decay channel in pp collisions with ALICE

Measurements of charm-hadron production provide a fundamental test of perturbative quantum chromodynamics (pQCD) calculations.
The theoretical framework has been developed based on the QCD factorisation approach, where results from $\mathrm{e}^{+}\mathrm{e}^{-}$ or $\mathrm{e}^{-}$p collision systems were used to tune the calculations.
However, comprehensive investigations of charm-hadron production, such as $\mathrm{D^0}$, $\mathrm{D^+}$, $\mathrm{D_{\mathrm{s}}^+}$ and $\Lambda_{\mathrm{c}}^{+}$, $\Xi_{\mathrm{c}}^{0,+}$ and $\Omega_{\mathrm{c}}^0$, in proton-proton (pp) collisions at the LHC raise the question of whether charm hadronisation is independent of the collision system.
These measurements show enhanced charm baryon-to-meson ratios compared to those observed in leptonic collision systems, indicating that theoretical models need to be modified to describe charm-baryon production in pp collisions.
Strange charm baryons, such as $\Xi_{\mathrm{c}}^{0,+}$ and $\Omega_{\mathrm{c}}^0$, have the potential to provide constraints on hadronisation models, since current calculations do not accurately reproduce the experimental measurements.
To achieve a better understanding of charm hadronisation in pp collisions, various measurements such as studies of charm-baryon production as a function of charged-particle multiplicity, are essential.
Furthermore, improving the precision of current experimental measurements is also crucial in order to provide valuable constraints on theoretical models.

In this contribution, the final results of the measurement of $\Xi_{\mathrm{c}}^{0,+}$-baryon production in different charged-particle multiplicity classes in pp collisions at $\sqrt{\it{s}}$ = 13 TeV, collected with the ALICE detector during LHC Run 2 data-taking period, are presented. In addition, a new measurement of the $\Xi_{\mathrm{c}}^{+}$-baryon production in pp collisions at $\sqrt{\it{s}}$ = 13.6 TeV is presented. In both measurements, the $\Xi_{\mathrm{c}}^{+}$ baryon is reconstructed via its hadronic decay channel, $\Xi_{\mathrm{c}}^{+}\rightarrow\Xi^-\pi^+\pi^+$.

Speaker: Jaeyoon Cho (Inha University (KR))

19:40 Measurement of b-jet cross section in pp collisions using graph neural networks with ALICE

The measurement of beauty-jet (b-jet) production in proton–proton (pp) collisions provides a stringent test of perturbative Quantum Chromodynamics (pQCD), owing to the large mass of the beauty quark, and serves as an essential baseline for b-jet studies in heavy-ion collisions. In particular, the excellent tracking and vertexing capabilities of the ALICE detector enable access to the low transverse-momentum ($p_\mathrm{T}$) region of b-jet production, where non-perturbative QCD effects become significant and theoretical uncertainties are large. Furthermore, the study of b-jet quenching in the low-$p_\mathrm{T}$ region of heavy-ion collisions is crucial for investigating the mass dependence of energy-loss mechanisms in the hot and dense QCD medium.

However, in heavy-ion collisions, the large combinatorial background significantly degrades the performance of conventional b-jet tagging methods based on impact-parameter or secondary-vertex reconstruction. The Graph Neural Network (GNN)-based b-jet tagging method shows a substantially superior performance compared to conventional methods in pp collisions and is expected to outperform the classical approaches also in heavy-ion collisions, despite any degradation due to background. Consequently, the implementation of a GNN-based method in ALICE is expected to enable low-$p_\mathrm{T}$ b-jet measurements in heavy-ion collisions with improved precision.

This poster presents a measurement of the b-jet cross section in pp collisions at $\sqrt{s}=13.6~\mathrm{TeV}$ using the GNN-based tagging method. The improved tagging performance of the GNN approach is discussed, together with future prospects for b-jet analyses in ALICE based on this method.

Speaker: Changhwan Choi (Pusan National University (KR))

CHChoi_HardProbes2026_poster.pdf

19:40 Measurement of direct-photon HBT with the photon conversion method in ALICE in Pb--Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.36 TeV

Direct photons provide a unique probe of the quark–gluon plasma (QGP), as they are emitted throughout all stages of the collision and escape the medium without strong final-state interactions. Correlations of direct photons with low transverse momentum enable access to the spatio-temporal evolution of the emitting source via Hanbury Brown–Twiss (HBT) interferometry.

In this contribution, the measurement of direct-photon HBT with ALICE is investigated using the Photon Conversion Method (PCM). In this method photons are reconstructed from electron–positron pairs originating from conversions in the detector material, allowing for an excellent momentum resolution at low transverse momentum. Together with the increased data-taking rate thanks to the ALICE Run 3 detector upgrade, this enables such a measurement for the first time with the PCM technique and opens the prospect of three-dimensional direct-photon HBT measurements.

This poster presents the current status of the analysis with a focus on the correlated background of the direct-photon HBT analysis in Pb--Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.36 TeV with ALICE in Run 3.

Speaker: Stefanie Mrozinski

Direct-Photon-HBT-Final.pdf

19:40 Measurement of jet invariant mass with semi-inclusive hadron+jet distributions in Zr+Zr and Ru+Ru collisions at $\sqrt{s_{\text{NN}}} = 200$ GeV with STAR

In relativistic heavy-ion collisions, jet quenching is a crucial phenomenon for understanding the interaction between hard-scattered partons and the hot, dense QCD medium known as the Quark–Gluon Plasma (QGP).
Jet observables, which serve as sensitive tools to test both perturbative and non-perturbative QCD, are significantly modified in the presence of the QGP. In particular, the jet mass ($M_{\text{jet}}$) is strongly correlated with the parton virtuality and its final-state radiation patterns. Therefore, measuring $M_{\text{jet}}$ in heavy-ion collisions provides a powerful probe of modifications to the evolution of parton virtuality induced by jet quenching.

In this poster, we present the $M_{\text{jet}}^2$ distributions corresponding to various jet transverse momentum ($p_{\text{T,jet}}$) ranges in Zr+Zr and Ru+Ru collisions at $\sqrt{s_{\text{NN}}} = 200$ GeV using the STAR detector and introduce a novel semi-inclusive hadron-triggered jet mass measurement methodology as a function of $(p_{\text{T,jet}}, M_{\text{jet}}^2)$. Jets, reconstructed by the anti-$k_{\text{T}}$ algorithm with various jet resolution parameters ($R = 0.2, 0.4$) are selected in the recoil region ($|\pi-\Delta \phi|< \pi/4$) with respect to trigger hadrons with $7 < p_{\text{T}} < 25 \,\text{GeV}/c$. As a method for uncorrelated background correction, the event-mixing technique is utilized, and yield-corrected distributions for different centrality classes $(0–10\%$, $60–80\%)$ are compared.
Fully corrected $M_{\text{jet}}^2$ distributions are also compared with the STAR-tuned PYTHIA6 at $\sqrt{s} = 200$ GeV to investigate medium-induced shifts and suppression of $M_{\text{jet}}^2$ distributions.

Speaker: jeongmyung kang (Sejong University)

19:40 Measurement of Jet Mass in $p+p$ Collisions at $\sqrt{s}=200$ GeV with the sPHENIX Experiment

Jet substructure measurements are powerful tools for studying the fragmentation and hadronization processes in vacuum, as well as for quantifying jet quenching effects due to the quark gluon plasma in heavy ion collisions. In particular, jet mass is sensitive to virtuality of the initial hard scattering and has been used for quark- and gluon-initiated jet separation. Measurements of jet mass in $p + p$ collisions also serve as the baseline for future studies in $Au+Au$ collisions and input to angularity measurements. The sPHENIX detector was designed to enable jet structure measurements with precision tracking and calorimetry. This poster presents the measurement of ungroomed ($m/p_{_T}$) in $p+p$ collisions at $\sqrt{s}=200$ GeV, using the sPHENIX calorimeters. The performance of this measurement is assessed by determining the mass energy scale and resolution. This work is an important step toward future sPHENIX jet substructure measurements in $Au+Au$ collisions and that incorporate tracking data.

Speaker: Mr Muhammad Ibrahim Abdulhamid (Georgia State University)

19:40 Measurement of Jet Nuclear Modification in heavy ion collisions for large jet area extending to Run3 with CMS detector.

Jet measurement in heavy ion collision is an important probe of Quark Gluon Plasma. Measurement of the jet nuclear modification in PbPb compared to PbPb collision can provide the insight into the jet quenching effect in Quark gluon plasma. In addition, the measurement of the jet spectra reconstructed using different distance parameter are of great interest to study the sensitivity of hadronization effect compared to the observables involving individual final state hadrons enabling to study the underlying jet quenching mechanism and the QGP properties. The nuclear modification factor in PbPb collision at 5.02 TeV was measured previously using CMS data (JHEP 05 (2021) 284) and the strong suppression was observed in the central collision for all jet area. Although the measurements were consistent with different theoretical model, systematic uncertainties were very large in previous measurements. In this talk, we will present the result for inclusive jet nuclear modification factor for PbPb extending the measurement to Run3 with CMS detector with larger data sets.

Speaker: Uttam Acharya (Vanderbilt University (US))

HP2026_UA_Poster.pdf

19:40 Measurement of the J/$\psi$ Fragmentation Function in pp Collisions at $\sqrt{s} = 13.6$ TeV with ALICE

In this study, jets containing a J/$\psi$ among their constituents are identified, and  the fragmentation function is defined as the longitudinal jet momentum fraction carried by the J/$\psi$ with respect to the jet. Measuring it provides insights into both quarkonium production and parton-shower dynamics, as well as the relation between these phenomena.
    The substantial upgrades of the ALICE detector in Run 3, most notably the implementation of a continuous readout mode, delivers a major increase of statistics for J/$\psi$ analyses at midrapidity. This leads to a strong reduction of uncertainties and, as a consequence, measurements of the fragmentation function can be performed with better granularity and extended kinematic reach, providing valuable input for further theoretical development. Proton–proton collisions provide a clean environment, constituting a crucial baseline for heavy-ion and QGP studies, areas for which ALICE is optimized and where phenomena that are not yet fully understood, such as J/$\psi$ suppression and charm-quark recombination, can be further investigated. 
    The measured observable will be presented separately for prompt and non-prompt J/$\psi$ mesons decaying into an electron-positron pair. The jets are reconstructed using the anti-k$_{\mathrm{T}}$ algorithm over a wide range of jet transverse momentum. The results will be compared to predictions by PYTHIA, as well as other state-of-the-art theoretical models.

Speaker: Lucas Ferrandi (University of Münster & University of São Paulo)

HP26Poster_v4.pdf

19:40 Measurement of the Lund jet plane in $pp$ collisions at $\sqrt{s}$ = 200 GeV with STAR

The Lund jet plane (LJP) is an experimental observable that maps the emission pattern of a jet onto a phase space representation of QCD radiation. Selecting on specific regions of the LJP allows one to isolate perturbative and non-perturbative contributions to the multi-scale evolution of a jet, making the LJP a powerful tool for precision jet substructure measurements. The primary LJP is constructed by stepping backward through the clustering tree following the hardest prong, or primary emitter, at each splitting. Emissions are characterized according to their splitting angle $\Delta R$, hardness $k_t$, and momentum-sharing fraction $z$ relative to the primary emitter.

We present our work toward the first measurement of the primary LJP at RHIC using $\sqrt{s} = 200$ GeV $pp$ collisions collected by the STAR experiment. Jets with resolution parameter $R = 0.4$ and transverse momenta $p_{T,jet} > 15$ GeV/$c$ are reconstructed from tracks and calorimeter towers in pseudorapidity $|\eta| < 1$. We include progress on Bayesian unfolding to correct for detector effects, and show PYTHIA predictions for comparison to the fully corrected data.

Speaker: Emily Pottebaum (Yale University (US))

HP2026poster_LJPatSTAR_pottebaum.pdf

19:40 Measurements of $D^{0}$ and $D^{*}$ production in p+p collisions at $\sqrt{s}$ = 510 GeV in the STAR experiment

Measurements of heavy flavor production in proton-proton ($p+p$) collisions are critical for testing perturbative QCD (pQCD) calculations and serve as an essential baseline for studying nuclear matter effects in heavy-ion collisions. In this presentation, we will report on the production of $D^0$ and $D^*$ mesons in $p+p$ collisions at a center-of-mass energy of $\sqrt{s} = 510$ GeV, utilizing the data collected by the STAR experiment at RHIC in 2017.

These charmed mesons are reconstructed via their hadronic decay channels, specifically $D^0 \rightarrow K^-\pi^+$ and $D^{*+} \rightarrow D^0\pi^+ \rightarrow K^-\pi^+\pi^+$ (and their charge conjugates). The signals have been extracted over a broad kinematic range, extending down to very low transverse momentum ($p_T$) with $0 < p_T < 2.1$ GeV/$c$ for $D^0$ and $2.0 < p_T < 6.0$ GeV/$c$ for $D^*$.

We will present the invariant cross-sections as a function of $p_T$, corrected for detector acceptance, reconstruction efficiency, and trigger biases. These measurements of the charm production cross-section will be compared with pQCD calculations to test the validity of the theoretical framework at this presented collision energy. The results will provide essential constraints on the energy dependence of charm production cross-sections, bridging the kinematic gap between RHIC and LHC energies and refining the theoretical baseline for heavy-ion studies.

Speaker: Subhadip Pal (Czech Technical University in Prague)

HP2026_poster_spal_final.pdf

19:40 Measurements of Energy Correlators from low to high multiplicity events in archived $e^{+}e^{-}$ ALEPH data

Measurements of hard probes in $e^{+}e^{-}$ collision data are essential components of parallel studies of hard probes in proton-proton and heavy-ion collisions as $e^{+}e^{-}$ collisions offer a true reference for such systems free from any hadronic initial state effects. Recently, a measurement of the two-point energy correlator using archived ALEPH e+e- data allowed the collinear and Sudakov limits of QCD to be studied simultaneously with the highest precision ever performed. In this talk, this recent measurement will be discussed and compared to a state of the art theoretical description, at NNLL accuracy in the collinear limit and NNNNLL accuracy in the back-to-back limit, achieving percent-level agreement. In addition, the event multiplicity dependence of these results, which is highly related to the understanding of EEC from small to large systems, will be shown for the first time. These results further investigate the presence of experimental signatures commonly attributed to collective phenomena in high-multiplicity $e^{+}e^{-}$ collisions, serving as an important baseline for measurements of these signatures in larger collision systems.

Speaker: Christopher Mc Ginn (Massachusetts Inst. of Technology (US))

hp2026_EPAEEC_CMcGinn_20260623_v4.pdf

19:40 Measuring thermal dimuons at high baryochemical potential with the NA60+/DiCE experiment at the CERN SPS

The high-intensity beams from the CERN SPS, available across a wide energy range, provide a unique opportunity to explore the QCD phase diagram at high baryochemical potential $\mu_B$. The NA60+/DiCE experiment, proposed to collect data from heavy-ion collisions at the SPS starting in 2030, has strong potential to investigate this diagram via precision measurements of electromagnetic probes in a beam-energy scan of Pb-Pb and p-A collisions at $\sqrt{s_{NN}} = 6-17$ GeV.

This talk will describe the NA60+/DiCE physics program for thermal dimuons. A precision measurement of the $\rho$ yield will enable a precise determination of the fireball lifetime and a search for anomalous behavior versus $\sqrt{s_{NN}}$ that could signal a first-order phase transition.
The experiment will also probe the $\rho$--$a_1$ chiral mixing mechanism, accessing $a_1$ properties via the thermal dimuon spectrum in the $1 < M < 1.4$ GeV range.
For masses above 1.5 GeV, the source temperature can be extracted directly by spectral fitting. NA60+/DiCE aims to determine, for the first time, a caloric curve (temperature vs. beam energy), focusing on $\sqrt{s_{NN}}<10$ GeV—a key region for mapping the phase transition at high $\mu_B$.

Finally, the competitiveness and complementarity of NA60+/DiCE in the landscape of future experiments will be discussed.

Speaker: Gianluca Usai (Universita e INFN, Cagliari (IT))

19:40 Modular Energy Loss Treatment (MELT) of high-momentum particles in a quark-gluon plasma

Recent efforts at the Large Hadron Collider have opened up new possibilities in studying jet modification and how jets lose energy in different system sizes. From $^{208}Pb$ to $^{16}O$, we observe varying jet energy loss based on the system size. This work presents a modular energy loss treatment (MELT) [1] in the NuclearConfectionery, tuned to central $^{208}Pb$ data. In $PbPb$ collisions, we are able to obtain a reasonable fit to $R_{AA}$ of all charged particles using both a linear and quadratic path-length dependence of energy loss. Using this tuned parameter set we then make predictions for $^{16}O$ and $^{20}Ne$ systems (including nuclear deformation effects in the initial state). We are able to reproduce the $R_{AA}$ in smaller systems and then make predictions for $v_2\{m\}$-$v_4\{m\}$ where $m=2,4$. We also explore new multi-particle cumulant observables with 2+ particles of interest.

[1] Kevin P. Pala et al. NuclearConfectionery: Multi-stage Simulation Framework for Modeling Relativistic Heavy-ion Collisions.
11 2025.

Speaker: Isaac Long (University of Illinois Urbana-Champaign)

Hard_Probes_2026_Poster.pdf

19:40 Non-Equilibrium Dynamics in QCD and Holography

The plasma generated in heavy ion collisions goes through different phases in its time evolution. While early times right after the collision are governed by far-from equilibrium dynamics, later times are believed to be well described by near-equilibrium dynamics. While the regimes of non-equilibrium are prohibitively complicated to describe within QCD, effective descriptions such as hydrodynamics provide a viable approach. In addition, holographic descriptions allow access to the full non-equilibrium dynamics at strong coupling. In this presentation, we review three examples of such hydrodynamic approaches and corresponding holographic descriptions: 1) propagation of non-equilibrium sound waves, 2) the non-equilibrium chiral magnetic effect, and 3) non-equilibrium shear viscosity.

Speaker: Matthias Kaminski

Kaminski_NonequilibriumDynamics_Poster_HP26.pdf

19:40 Observable sensitivity to evolution of charm quark in the early phases of relativistic heavy-ion collisions

Heavy quarks are predominantly produced in the initial hard scatterings of relativistic heavy-ion collisions and therefore have direct access to the early stages of the collision event. We study the sensitivity of open heavy-flavor observables to the pre-equilibrium stage of the medium evolution in Pb+Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV. The space-time evolution of the bulk medium is modeled using the IP-Glasma+MUSIC+UrQMD framework, which provides a realistic description from the earliest times through the hadronic phase. Charm quarks are initialized using PYTHIA and their in-medium propagation is simulated via Langevin dynamics implemented within the MARTINI framework [1]. While substantial momentum broadening of charm quarks is observed during the earliest stages of the collision, we find that the resulting D-meson $R_{AA}$, $v_2$ and angular correlations exhibit only a weak sensitivity to pre-equilibrium interactions. Our results suggest that the late-time medium effects dominate the observed heavy-flavor suppression and anisotropic flow. We review the elements that lead us to this conclusion.

1. M. Singh, M. Kurian, B. Schenke, S. Jeon, and C. Gale, arXiv:2509.18647

Speaker: Mayank Singh (Vanderbilt University)

HP_2026_poster.pdf

19:40 Open charm production in fixed-target mode at LHCb

The LHCb experiment has pioneered a unique fixed-target program at the LHC, which has been upgraded for Run 3 with the new SMOG2 system. This device provides improved confinement of the gaseous target, resulting in a substantial increase in fixed-target luminosity. In addition, SMOG2 introduces for the first time the possibility to inject non-noble gases, thereby expanding the range of accessible collision systems. These upgrades enable high-statistics studies of open charm production in proton–nucleus collisions. Charm production measurements in this environment provide unique insights into cold nuclear matter effects-such as nuclear PDF modifications, parton energy loss, and intrinsic-charm contributions—across small and large collision systems at the same center-of-mass energy per nucleon pair. In this talk, we will present recent measurements of open-charm production in proton–nucleus fixed-target collisions with the LHCb experiment.

Speaker: Sharelle Habah Yazzie (LANL)

19:40 Operation and performance of the sPHENIX vertex detector

The Monolithic Active Pixel Vertex Detector (MVTX) is the innermost tracking detector of the sPHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) and essential for reconstructing short-lived charm and beauty hadrons. It consists of three concentric layers of detector material, utilizing the ALICE Pixel Detector (ALPIDE) ASIC. The detector covers a radial range from 2.5 cm to 4.5 cm from the beam line and provides precise measurements of primary and secondary vertices. These layers provide high spatial resolution and strong tracking performance. Each sensor is 50 μm thick and features pixels of size 29 × 27 μm arranged in a matrix of 1024 × 512. The sensors are fabricated using 180 nm CMOS technology and achieve a hit resolution better than 6 μm. The sensing elements and readout electronics are integrated on a single silicon chip. Across its three layers, the MVTX comprises 48 staves and 432 ALPIDE sensors, resulting in over 226 million pixels that provide complete and robust tracking coverage. Each pixel chip performs signal amplification, digitization, and zero suppression directly on chip, which reduces data volume and improves readout efficiency. The MVTX has operated in triggered heavy ion collisions and streamed proton-proton collisions. We will show the MVTX's vertexing performance and its relation to the rest of the sPHENIX system to unlock sPHENIX's full heavy flavor potential.

Speaker: Iftekhar Ahmed (University of Tennessee, Knoxville)

19:40 Photon Production, Photon Enhancement and Photon Absorption in a Monte Carlo Framework

We have modified the X-SCAPE framework to create a Monte Carlo event generator which allows the computation of direct photon production in A+A collisions, and is well-tuned to the hadronic sector of nuclear collisions [1]. State-of-the-art rates for photon production from QGP and hadron matter have been implemented. Beyond that, our focus has been on the testing of two paradigms. One, argued over the past decade, is a postulated “critical enhancement” of photon rates around the critical temperature [2]. The other, which is usually taken for granted, is Thoma’s prediction of an effectively infinitely large mean-free path, ~500 fm, for photons in nuclear collision systems [3]. We argue that with modern photon rates the mean-free path can be much smaller. Hence, photon reabsorption could become a non-negligible effect in large systems. We discuss these paradigms and present calculations exploring the different possible scenarios. We will also address if these ideas can help improve the theoretical description of direct photon data from RHIC and LHC.

[1] Multisystem Bayesian constraints on the transport coefficients of QCD matter, D. Everett et al. [JETSCAPE Collaboration], Phys.Rev.C 103 (2021) 5, 054904.
[2] Pseudo-critical enhancement of thermal photons in relativistic heavy-ion collisions, H. van Hees, M. He, and R. Rapp, Nuclear Physics A 933 (2015), 256–271.
[3] Damping rate of a hard photon in a relativistic plasma, M. H. Thoma, Phys. Rev. D 51 (1995), 862–865.

Speaker: Rainer Fries (Texas A&M University)

HP2026_Photons_Parker.pdf

19:40 Probing Jet Quenching Dynamics with Higher-Point Energy Correlators

Energy correlators have emerged as powerful jet substructure observables due to their ability to disentangle physics across scales, suppress soft contamination, and connect cleanly to underlying theory. While two-point correlators have received a lot of attention, higher-point correlators remain largely unexplored, in part because their evaluation is very computationally expensive in the high-multiplicity environment of heavy-ion collisions. We recently introduced a parametrization of higher-point correlators (Phys. Rev. Lett. 134 (2025) 23, 231902) that enables the rapid computation of projected higher-point correlators, retaining overall scale information while integrating out shape dependence, with the computational cost comparable to the two-point case.

Building on this framework, we introduce resolved energy correlators that are sensitive to detailed jet radiation patterns by retaining some of the shape information, while maintaining computational efficiency. We show their potential for studying aspects of jet-medium interactions, including medium response (the wake) and the quasi-particle nature of the medium (Molière scattering). Because a single jet already yields a non-trivial distribution for the energy correlator, we develop new statistical tools designed to capture subtle intra-event correlations to robustly quantify medium-modification effects.

Speaker: Arjun Srinivasan Kudinoor (Massachusetts Institute of Technology)

Arjun_Kudinoor_HP2026_Poster.pdf

19:40 Probing nuclear geometry with flow measurements in fixed-target collisions at LHCb

In heavy-ion collisions, collective flow is thought to arise from the geometric overlap of the colliding nuclei, which generates pressure gradients within the medium. Thanks to the diverse fixed-target data samples collected by the LHCb experiment, it is possible to study the influence of nuclear geometry on final-state particle correlations by comparing targets with different shapes. This contribution presents recent results on collective flow measurements in heavy-ion fixed-target collisions, including PbNe and PbAr, showing a strong influence of the nuclear geometry, predicted by the latest theoretical calculations.

Speaker: Haley Delgarito (LANL)

19:40 Probing the Dead Cone Effect with $D^0$-tagged Jet Energy Correlators in STAR

Perturbative QCD calculations indicate that asymptotically free heavy quarks are less likely than lighter flavors to emit gluonic radiation at small angles, a phenomenon called the Dead Cone Effect (DCE). $D^0$-tagged jets at RHIC collider energies offer a near ideal regime to probe this effect, due to the kinematic suppression of gluon jets energetic enough to produce charm pairs--which are likely to be misreconstructed with net charm. Measurements of DCE at the LHC must contend with this challenging "charm-subjet" contribution in abundance, making a low-energy RHIC measurement essential to gain clear perspective on the mass dependence of gluonic radiation in QCD.

This poster presents the early stages of a DCE measurement at STAR using Energy-Energy Correlators (EECs), including simulation studies with PYTHIA and $D^0$-tagged jet reconstruction in $pp$ collisions at $\sqrt{s}=200$ GeV. EECs, energy-weighted angular correlations between hadrons in a jet, are infrared/collinear (IRC)-safe observables shown to be sensitive to DCE.$^1$ The persistence of EEC signals across the IRC divergences of QCD enable the direct comparison of EEC measurements to theoretical pQCD predictions. Through feasibility studies and initial results, we see compelling promise of this EEC measurement to reveal the Dead Cone at RHIC.

[1] E. Craft, K. Lee, B. Meçaj, and I. Moult, Beautiful and Charming Energy Correlators, (2022), arXiv:2210.09311 [hep-ph].

Speaker: Ryan James Hamilton (Yale University (US))

Hamilton_HP2026_CharmEEC_Poster_Draft3.5.pdf

19:40 Production of \psi(2S) in jets using Fragmenting Jet Function framework

Recent LHCb measurements (2410.18018) of the transverse momentum distribution of prompt $\psi$(2S) production in jets from $pp$ collision at the centre-of-mass energy of 13 TeV cannot be explained by fixed order NRQCD followed by naive PYTHIA shower. We use two different frameworks: Fragmenting Jet Functions + NRQCD and Gluon Fragmentation Improved PYTHIA to study the production of $\psi$(2S). Both these approaches provide a much better description of the data in the $\eta_{\text{jet}}=2.5-4.0$ and different $p_T$ bins in the $15-60$ GeV/c range. These frameworks shed light on the production mechanism of the $\psi$(2S) at the LHC and can be used to extract the nonperturbative NRQCD long distance matrix elements.

Speaker: Yu Fu (Duke university)

Psi(2S)_HP2026.pdf

19:40 Properties of open heavy-flavor probes from lattice QCD

In this talk, I will discuss heavy-flavor probes from lattice QCD, focusing on the heavy-quark diffusion coefficient, the temperature-dependent heavy-quark (charm and bottom) masses, and the mean thermal velocity squared $\langle v^2\rangle$ of heavy-flavor degrees of freedom in the QGP.

The heavy-quark diffusion coefficient is obtained from lattice-QCD calculations inspired by Heavy Quark Effective Theory, in which we compute chromo-electric and chromo-magnetic correlators on fine lattices with temporal extent $N_{\tau}=16-28$. We determine the diffusion coefficient for both charm and bottom quarks over a wide temperature range, from 160 MeV to 1000 MeV.

In addition, we compute generalized charm and bottom susceptibilities over a broad range of temperatures. We find that these results are well described by a quasi-particle description, which allows us to extract an effective, temperature-dependent heavy-quark mass and the mean thermal velocity squared $\langle v^2\rangle$ for charm and bottom degrees of freedom in the QGP.

Speaker: Jorge Luis Dasilva Golan (Brookhaven National Laboratory)

19:40 Quantifying chaos and instabilities in Glasma via Lyapunov exponents

The initial state in ultrarelativistic heavy-ion collisions is described by the Color-Glass Condensate (CGC) framework, where the collision of two colored glass sheets produces strong, coherent gluon fields known as the Glasma. The subsequent evolution of these classical colored fields is governed by the Classical Yang-Mills (CYM) equations. We study the growth of instabilities in expanding Glasma fields by introducing controlled spectral perturbations to the electric fields and gauge links. We employ Fast Fourier Transforms to implement various filters in momentum space, including Gaussian, power-law, and narrow-band forms, allowing us to excite and isolate specific momentum modes. By tracking the difference between two initially close gauge-field configurations via the measures $\mathrm{Tr}(\delta E_\eta)^2$ and $\mathrm{Tr}(\delta B_\eta)^2$, where $E_\eta$ and $B_\eta$ are the longitudinal colored electric and magnetic fields, we observe an exponential growth of unstable modes following the functional form $e^{\lambda \sqrt{g^2 \mu \tau}}$, where $\tau$ is proper time, $g$ is the coupling constant, and $g^2\mu \sim Q_s$ with $Q_s$ being the saturation scale. Remarkably, for all perturbation kernels and strengths studied, we find a consistent Lyapunov exponent $\lambda \sim 0.4$, indicating a robust chaotic amplification that is largely insensitive to the spectral details of the initial perturbation. Moreover, we extend this chaotic analysis to the transport of hard probes, studying the trajectories of heavy quarks propagating through the evolving non-Abelian fields via Wong's equations.

Speaker: Ms Pooja - (University of Jyväskylä)

Pooja (Hard probes 2026 Poster).pdf

19:40 Quantifying vacuum-like jets in heavy-ion collisions: a Machine Learning study

The modification of jets by interaction with the Quark Gluon Plasma has been extensively established through the comparison of observables computed for samples of jets produced in nucleus-nucleus collisions and proton-proton collisions. The presence of vacuum-like jets, jets that experienced little interaction with the Quark Gluon Plasma, in the nucleus-nucleus samples dilutes the overall observed modification hindering the detailed study of the underlying physical mechanisms. The ability to ascertain on a jet-by-jet basis the degree of modification of a jet would be an invaluable step in overcoming this limitation. We consider a Transformer classifier, trained on a low-level representation of jets given by the 4-momenta of all its constituents. We show that the Transformer is able to capture discriminating information not accessible to other architectures which use high-level physical observables as input. The Transformer allows us to identify, in the experimentally relevant case where both medium response and underlying event contamination are accounted for, a class of jets that have been unequivocally modified. Further, we perform a robust estimate of the upper bound for the fraction of jets in nucleus-nucleus collisions that are, for all purposes, indistinguishable from those produced in proton-proton collisions.

https://inspirehep.net/literature/2872254

Speaker: João A. Gonçalves (LIP - IST)

HP2026_Poster.pdf

19:40 Quarkonium suppression with QTRAJ 1.1 beyond the dipole

The Open Quantum System (OQS) framework offers a method for calculating quarkonium observables during and after its propagation through a medium, under a fully quantum description. The QTRAJ code efficiently simulates the propagation of quarkonium in a medium when the latter sees quarkonium as a small color dipole $rT \ll 1$. While this limit is accurate for $\Upsilon(1S)$, its applicability to other quarkonium states is unclear. In this talk, we present a generalization of this code that incorporates the regime where $rT \sim 1$ in the one-gluon exchange approximation. We will outline the updates in the algorithm required to go from QTRAJ 1.0 to 1.1 and then we will show predictions for observables such as the nuclear modification factor as a function of $N_{part}$ or $p_T$.

Speaker: Mr Jorge Manuel Martínez Vera (Università di Torino & Universitat de Barcelona)

HP2026.pdf

19:40 Radius Dependence of Jet Quenching in Central Pb+Pb Collisions at $\sqrt{s_{NN}}=5.02~\mathrm{TeV}$ with $R_{AA}^{R/0.2}$ and $S_{\mathrm{loss}}$

The jet-radius dependence of the nuclear modification factor $R_{AA}$ probes how energy lost by partons in the quark-gluon plasma is redistributed in angle. Its interpretation, however, is entangled with the steeply falling jet spectrum and selection biases. This poster presents a comparative, data-driven study of radius-differential jet quenching in central (0-10%) Pb+Pb collisions at $\sqrt{s_{NN}}=5.02~\mathrm{TeV}$. We analyze published ATLAS measurements for inclusive, photon-tagged, and dijet selections, together with ALICE charged-jet results using two complementary observables: the $R_{AA}$ double ratio $R_{AA}^{R/0.2}\equiv R_{AA}(R)/R_{AA}(0.2)$ and the fractional energy loss $S_{\mathrm{loss}}$. We observe strong selection- and measurement-dependent differences: ATLAS dijet double ratios exceed unity at larger $R$, while ALICE charged-jet double ratios are below unity. By exploiting $S_{\mathrm{loss}}$ to mitigate spectral bias, we observe an ordering of the extracted energy loss across selections in the kinematic range studied, with sub-leading dijets exhibiting the largest shifts and $\gamma$-tagged jets the smallest. These results underscore the competing roles of out-of-cone energy transport and selection bias, and provide radius-resolved, data-driven constraints for models of jet quenching.

Speaker: Rafet Kavak (Univ. Illinois at Urbana Champaign (US))

rafet_kavak_HP2026_poster.pdf

19:40 Reconstructing γ→e+e- with the sPHENIX detector at RHIC

A photon encountering high density matter will probabilistically undergo pair production, resulting in a lepton-antilepton pair that can be detected to reconstruct the incident photon. This analysis uses proton-proton data collected by the sPHENIX detector to reconstruct conversion photons via the dielectron channel. Tracks are fitted to data collected by sPHENIX’s Time Projection Chamber (TPC). Electron and positron candidates are identified using an invariant mass analysis. Tracks identified as daughter candidates are matched to energy clusters in the Electromagnetic Calorimeter (EMCal), and momenta are extracted from the track curvature. The purity of the daughter candidates is verified using the energy to momentum ratio, E / p. This analysis sets the ground work for searches for higher mass resonances reconstructed using the dielectron channel, enabling the reconstruction of charmonia and bottomonia, a vital component of sPHENIX’s heavy-flavor program.

This work is funded by DOE grant # DE-SC0023491, as well as the Dr. Hyo Sang Lee Graduate Fellowship from the College of Arts and Sciences at Lehigh University.

Speaker: Valerie Wolfe (Lehigh University)

VW_POSTER_HP.pdf

19:40 Riders on the Flow: A New and Efficient Method to Compute Jet Wakes

The interaction of jets with a droplet of QGP leads not only to modifications of the parton shower but also to modifications of the droplet itself, with both effects contributing to modifications of jets seen in a detector. Empirical determination of how the medium responds to the passage of a jet will add to what we know about the jet-medium interaction and will provide a unique window into the process of hydrodynamization.

As part (or even the whole) of a jet melts into the flowing medium, details about the orientation of the jet with respect to that of radial flow, or the time it takes for the excited hydrodynamic modes to reach the freezeout hypersurface, have a measurable effect on the distribution of the hadrons-after-freezeout that originate from the wake. Addressing the vast landscape of possible configurations of jets in medium (variation in jet fragmentation and substructure, point of origin in the flowing fluid, jet direction relative to fluid flow) in realistic models is not only necessary for a meaningful phenomenology, but also an arduously expensive computing task. In practice, one needs to compute a full 3+1D hydrodynamic evolution that includes the source terms due to the deposition of energy and momentum by the jet, with a sufficiently fine grid which captures the subtle features of the wake in the flowing fluid, for each jet.

In this talk we present a new semi-analytic method with which to reduce the computation of the wake profiles at the hypersurface to almost zero computational time after an initial investment in creating templates. It relies on a Green’s function approach where the profiles obtained for wakes evolving in pure Bjorken flow are mapped into a realistic evolution possessing radial flow by means of the appropriate set of coordinate transformations. We demonstrate that our method correctly describes the dynamics arising from any type of source configuration via explicit benchmark comparisons to full 3+1D hydrodynamics with the same source terms. This new method provides a tractable way to include realistic medium response physics in the Hybrid strong/weak coupling model, which will improve predictions for essentially every ungroomed jet-related observable, and many groomed observables, due to the overall hardening and narrowing of the distribution of hadrons from the wake as compared to that coming from a wake which does not couple to the background radial flow.

Speaker: Xiaojun Yao (University of Washington)

19:40 Search for Diffusion Wake Signatures in Dijet Systems via Rapidity Asymmetry of Jet-Hadron Correlations in $\sqrt{s_{NN}}=200$ GeV Au+Au Collisions at STAR

Jet-medium interactions in heavy-ion collisions are expected to generate a characteristic hydrodynamic response consisting of a forward wake front and a backward diffusion wake. Direct observation of the depletion of soft hadrons behind the jet characteristic of the diffusion wake has proven difficult due to background and overlapping jet induced structures. Recent theory suggests that dijets with a finite pseudorapidity separation provide a clean handle: the diffusion wake of the recoiling jet is shifted in rapidity, allowing for the measurement of the corresponding depletion in soft hadrons via asymmetry in jet-hadron correlations [1]
.
We present a novel search for this signal in $\sqrt{s_{NN}}=200$ GeV Au+Au collisions at STAR, compared against dijets from $\sqrt{s}=200$~GeV $p$+$p$ collisions, where QGP is not expected to form. Jets are reconstructed with the anti-$k_{T}$ algorithm and dijet events are grouped by rapidity gap between the leading and subleading jet axes. By comparing per-dijet associated jet-hadron correlations for large and small gap dijets, we construct a rapidity asymmetry observable using soft hadrons that suppresses contributions from the underlying event and radial flow. The distribution of associated hadrons $\Delta N_{AA}$, defined as

$\Delta N_{AA} = \int d\Delta\phi \left[\frac{dN_{AA}}{d\Delta\phi d\Delta\eta} - \frac{dN_{pp}}{d\Delta\phi d\Delta\eta} \right]$,

is constructed for dijet events with and without a finite rapidity gap. The difference is taken between $\Delta N_{AA}$ for dijets with a rapidity gap and dijets without a rapidity gap to arrive at the final observable. A track $p_{\rm{T}}$ range of $1.0$ GeV/$c < p_{\rm{T}}< 2.0$ GeV/$c$ is applied to suppress contribution to the signal from radial flow. We report preliminary results and assess sensitivity to diffusion wake driven depletion structures, providing new constraints on jet induced medium response at RHIC.

[1] Z.~Yang and X.-N.~Wang, Rapidity Asymmetry of Jet--Hadron Correlation as a Robust Signal of Diffusion Wake Induced by Dijets in High-Energy Heavy-Ion Collisions, Phys. Rev. Lett. 135, 072302 (2025).

Speaker: Gabriel Dale-Gau (Czech Technical University in Prague)

HP2026_Poster_GDG_v5.pdf

19:40 Soft-dielectron measurement in pp collisions at $\sqrt{s}$=13.6 TeV with ALICE in Run 3

Low-mass dielectrons present an exceptional tool to deepen our understanding of the particle production in hadronic collisions. As they are produced during all stages and are unaffected by the strong interaction, they keep the information of their original production mechanism. This allows dielectrons to probe the soft regime of QCD which is often inaccessable otherwise.\
At the Intersecting Storage Rings (ISR) at CERN, an excess of dielectron pairs over the expectation from know dielectron sources had been measured by the AFS experiment at low invariant mass and small pair momenta in pp collisions at $\sqrt{s} = $ 63 GeV. A similar kinematic regime can be accessed with ALICE by reducing the magnetic field of the central barrel solenoid. First results from Run 2 indicate an excess also at LHC energies, but the limited precision of the data did not allow for a final conclusion. With the upgrade of the ALICE detector for Run 3 much higher data-taking rates can be achieved increasing the event statistics by a factor of about 400 compared to Run 2.\
In this poster, a first look at pp collisions at $\sqrt{s}=$ 13.6 TeV taken with reduced magnetic field of $B=0.2$ T will be presented and their potential to address the excess observed in Run 2 and at the ISR will be discussed.

Speaker: Belana Lubinski (Goethe University Frankfurt (DE))

Poster_HP2026_lowB.pdf

19:40 Solving the Boltzmann equation for heavy quarks using heavy quark phonon effective theory ($\phi$-EFT)

An excellent probe for the thermalization of the QGP and its dynamics are heavy quarks, since they are created during the initial stages of the collision. If given enough time, these heavy quarks will thermalize with the QGP medium and follow its collective dynamics. The precise thermalization dynamics is hard to describe from first principles, especially at low momenta, since it is governed by non-perturbative QCD in this regime. An alternative way of describing this strongly coupled regime is via an effective field theory (EFT), based on the interaction of the heavy quarks with the collective modes of the QGP (phonons, arXiv:2510.13942). In this work we use this EFT and its description of the interactions between phonons and heavy quarks to calculate the collision kernel appearing in the Boltzmann equation. Then, we solve the Boltzmann equation for the heavy quark distribution and examine its thermalization in the QGP via soft phonon interactions. Finally, we compare the thermalization process and rate via phonon exchange with that obtained from collision kernels based on perturbative QCD calculations.

Speaker: Noah Koliadko

Poster.pdf

19:40 sPHENIX Calorimeter Jet Substructure Measurements with Jet Reclustering

The sPHENIX detector at Brookhaven National Laboratory’s Relativistic Heavy Ion Collider (RHIC) is a state-of-the-art jet and heavy flavor physics detector that includes hadronic calorimetry at mid-rapidity for the first time at RHIC. During the p+p $\sqrt{s}$ = 200 GeV run in 2024, 107 pb$^{−1}$ of pp collisions were sampled using high $p_T$ jet triggers. The presence of the Quark Gluon Plasma (QGP) in heavy ion collisions impacts jet substructure, giving insight into the nature of the QGP itself. Measurements of jets and jet structure in p+p collisions provide an important baseline for these measurements in heavy ion collisions. This poster will discuss initial jet substructure measurements using only calorimetric information by first clustering calorimeter towers into Anti-$k_T$ R = 0.2 ”constituent” jets before reclustering them into Anti-$𝑘_𝑇$ R = 0.4 jets for substructure study through use of the soft-drop algorithm. We will show the current status of this study, in both simulation and p+p data.

Speaker: Noah Applegate (Iowa State University)

19:40 sPHENIX foundation model development for reconstruction and analysis

Foundation models are a generalized type of large language model (LLM) that are trained on large, diverse, unlabeled datasets and can perform a variety of downstream tasks. The success of LLMs in industry has motivated research into their application in scientific domains. High energy nuclear and particle physics experiments, such as sPHENIX, produce vast amounts of sparse, low-level data that could be trained to perform reconstruction tasks. In this talk we will discuss recent work on the application of a foundational model to sPHENIX Time Projection Chamber (TPC) data [arXiv:2508.14087] and its performance with several TPC-related downstream tasks. The implications of Foundation Models, including additional challenges that they could address, will be highlighted.

Speaker: Mariia Mitrankova

sPHENIX_HP26_foundation_model_Mitrankova_v2.pdf

19:40 sPHENIX novel use of generative AI for physics measurements

Generative artificial intelligence (AI) has been transforming industry and science. sPHENIX, a new experiment at RHIC, has been at the cutting edge in adopting innovative generative AI to accelerate simulation, reconstruction, and analysis in a robust manner. In this talk we will highlight two recent works on diffusion-model-based, full-detector simulations of full-event heavy ion collisions [DOI: 10.1103/PhysRevC.110.034912 ] and heavy ion background subtraction on calorimeter jets using unsupervised generative learning [arXiv:2510.23717]. The implications of these new technologies for the sPHENIX QGP physics program will be highlighted, including for strange and heavy flavor and strange probes of the medium.

Speaker: Cameron Dean (Massachusetts Inst. of Technology (US))

GenAI_CDean_20260623.pdf

19:40 sPHENIX probes of multiparton interaction and QCD radiation in jet events in p+p collisions

Soft particle production accompanying a hard scattering in proton-proton (p+p) collisions arises from a variety of sources, including multiple parton interactions, initial- and final-state radiation, and the color neutralization of the beam remnant. Quantifying the underlying event associated with a high energy jet provides sensitivity to these contributions and their interplay with the hard process. In this talk, we present a new measurement of the transverse energy in the region transverse in azimuth to the leading jet using the large p+p data set collected in 2024 with the sPHENIX detector at RHIC. The underlying event activity is reported as a function of leading jet kinematics, including the highest jet p$_T$ regions where the partitioning of the collision energy between the hard scattering and the underlying event is of particular interest. Comparisons to event generators such as PYTHIA and HERWIG are shown to assess model sensitivity to multiple parton interactions and QCD radiation at RHIC energies. We also discuss comparisons with underlying event measurements at other center-of-mass energies, from RHIC to LHC scales, to evaluate the evolution of these contributions with collision energy and hard scattering process.

Speaker: Benjamin Kimelman (Vanderbilt University)

pp_UE_poster_HP26_final.pdf

19:40 sPHENIX streaming readout of tracking detectors for novel measurements in high-rate, unbiased p+p data

The sPHENIX experiment is a next-generation collider detector at RHIC that completed data taking in early 2026, collecting large data sets in 200 GeV p+p and Au+Au collisions. sPHENIX is designed to study rare jet and heavy flavor probes of the Quark-Gluon Plasma using full calorimetry and tracking. In addition to calorimeter-triggered events, a unique hybrid and 100% streaming readout scheme for the tracking system allows unbiased p+p tracking data to be recorded at rates of up to 800 kHz. The resulting data sample is very large and unbiased, and provides access to open heavy flavor decays that cannot be conventionally triggered on, opening up significantly new physics capabilities in p+p collisions at RHIC. In this talk we will describe the streaming readout of the tracking detectors, the reconstruction approach, and the evaluated performance.

Speaker: Hao-Ren Jheng (Massachusetts Inst. of Technology (US))

Poster_HP26_HRJheng.pdf

19:40 Strangeness production at LHCb

The production of strange hadrons in high-energy collisions offers valuable insight into hadronization, parton fragmentation, and nuclear effects. While strangeness enhancement has been associated to quark-gluon plasma formation in heavy-ion collisions, recent observations in small systems challenge conventional hadronization models. In this context, proton–nucleus collisions offer a valuable testing ground to study cold nuclear matter effects and nuclear modifications. To shed light on this complex scenario, the LHCb detector, with its unique forward acceptance and excellent particle identification, enables detailed studies of strangeness production in both collider and fixed-target modes over a unique kinematic range. New results on strange hadron production will be presented, providing new constraints on hadronization dynamics and nuclear effects in small systems.

Speaker: Cesar Luiz Da Silva (Los Alamos National Laboratory (US))

19:40 Studies of $\phi$-meson production at LHCb

The $\phi$ meson provides a unique probe of strange-quark dynamics in high-energy nuclear collisions. Its mass lies at the boundary between perturbative and nonperturbative QCD, making $\phi$-mseson production sensitive to both regimes. In heavy-ion collisions, $\phi$-meson production is particularly senstive to strange-quark coalescence in quark-gluon plasma. Owing to its zero net strangeness, measurements of $\phi$-meson production help disentangle the physical mechanisms behind strangeness enhancement in high-energy hadron and nuclear collisions. The excellent hadron identification capabilities of the LHCb detector enable precise studies of $\phi$-meson production in nuclear collisions. Furthermore, the SMOG system allows LHCb to investigate $\phi$ production in fixed-target collisions. New measurements of $\phi$-meson production in both collider and fixed-target configurations are presented.

Speaker: Jiazhao Lin (Indiana University (US))

20260621_HP_v2.pdf

19:40 Studying properties of baryon-dominated matter with dileptons

The High Acceptance Di-Electron Spectrometer (HADES) experiment has measured virtual photons in heavy-ion collisions as well as in protonand ion-induced reactions in the energy range of a few GeV. Thanks to the penetrating nature of electromagnetic probes, this allows to study thermal and microscopic properties of hadronic matter in the high netbaryon density and moderate temperature region of the QCD phase diagram.

In this contribution, we focus on multi-differential spectra and collective azimuthal flow patterns of dilepton sources in Au+Au collisions at $\sqrt{s_{NN}} = 2.42$ GeV and Ag+Ag collisions at $\sqrt{s_{NN}} = 2.55$ and 2.42 GeV in comparison with hadronic probes sensitive to the freeze-out stage. It is now accompanied by the measurements in p+p reactions at $\sqrt{s_{NN}} = 2.55$ and 3.46 GeV serves as a baseline for dilepton studies in heavy-ion collisions at HADES and facilities, including FAIR.

Very soft dileptons are predicted to be sensitive to electrical conductivity of the medium and to precursor phenomena in the vicinity of the transition to color-superconducting phases. This motivated dedicated runs at HADES with magnetic fields strength reduced to 5% of the maximum value and increased acceptance for low-momentum leptons. We will discuss the essential steps towards the study of such soft dileptons.

We also give an outlook to the analysis of new HADES data at even lower beam energies that further extend excitation functions of dilepton observables

Speaker: Sukyung Kim (HADES)

19:40 System-size dependence of charged-particle $R_{\mathrm{AA}}$

Jet quenching phenomena in ultrarelativistic nucleus–nucleus collisions arise from the energy loss of high-energy partons propagating through the quark–gluon plasma, leading to a suppression of high-$p_{\mathrm{T}}$ particle yields. While strong suppression has been observed in heavy-ion collisions, its dependence on the size of the nuclear system has not yet been systematically measured. We present a comparative study of high-$p_{\mathrm{T}}$ charged-particle nuclear modification factors across four collision systems, based on measurements performed by the CMS experiment at the LHC. Existing results in oxygen–oxygen, xenon–xenon, and lead–lead collisions are recast using a common $p_{\mathrm{T}}$ binning and extended with the first measurement of charged-particle $R_{\mathrm{AA}}$ in neon–neon collisions at $\sqrt{s_{\mathrm{NN}}}=5.36$ TeV. By presenting the suppression patterns as functions of $p_{\mathrm{T}}$ and the nuclear mass number $A$, this study provides new experimental leverage on the system-size dependence of parton energy loss and constrains the path-length and medium-density dependence of jet quenching in QCD matter.

Speaker: Abraham Thomas Holtermann (Massachusetts Inst. of Technology (US))

SystemSizev3.pdf

19:40 Systematic effects in resonance signal extraction with the ALICE detector

Resonance measurements in high-energy nuclear collisions require reliable extraction of signal yields in the presence of large combinatorial backgrounds (e.g. Event Mixing, Like-Sign). Both the background estimation technique and the invariant-mass fitting strategy can significantly influence the stability of the extracted signal and contribute to systematic uncertainties across a broad transverse-momentum range.

This poster presents a comparative study of commonly used combinatorial background subtraction methods together with different invariant-mass fitting approaches, including a direct comparison of implementations in the ROOT and RooFit frameworks. The impact of these methodological choices on fit stability, convergence behavior, parameter correlations, and relative variations of the extracted resonance signal is evaluated as a function of transverse momentum.

The analysis focuses on methodological robustness rather than final physics results, providing guidance for systematic uncertainty estimation in resonance analyses performed with the ALICE detector. The presented techniques are broadly applicable to studies using modern collider detectors and are particularly relevant for high-momentum hadron and correlation measurements in environments with large combinatorial backgrounds.

Speaker: Veronika Barbasova (Pavol Jozef Safarik University (SK))

Poster_HP2026_v4.pdf

19:40 Time-Based Reclustering for Identifying Early Jet Splittings in pp Collisions with ALICE

Jets are formed in the initial hard scattering of a collision and thus experience multiple scales of QCD processes. In proton-proton collisions, we may study how colored partons radiate and fragment using differential jet substructure, made possible by the ALICE detector’s low-momentum reach and high-precision tracking. More specifically, by de-clustering the jet fragmentation history splitting-by-splitting, we seek to access the earliest stages of jet evolution.

This de-clustering is commonly performed using the Cambridge-Aachen (C/A) algorithm, which invokes angular-ordering of QCD emissions to arrange the splittings from widest to narrowest. In this work, we instead present results of groomed jet substructure for jets de-clustered using the τ algorithm, which orders splittings based on the formation time (τ_form). In comparing these two algorithms in the vacuum conditions of pp collisions, we find differences that highlight sensitivity to the underlying ordering variable and are important for extending MC generators to higher orders.

These results also establish a baseline in pp collisions and motivate future applications in Pb-Pb collisions at 5.36 TeV, where the medium-induced emissions may not respect angular-ordering, and where an ordering on formation time may help tune the degree of quenching. Reliably de-clustering jets in Pb-Pb collisions will allow for investigation into modifications to jet substructure made by the medium.

Speaker: Morgan Bailey Knuesel (Yale University (US))

Time-Based Reclustering for Identifying Early Jet Splittings in pp Collisions with ALICE (final).pdf

19:40 Toward a Complete Description of Partonic Interactions in JETSCAPE

Partonic interactions play a crucial role in understanding the space–time evolution of the quark–gluon plasma (QGP) formed in high-energy nuclear collisions. Early efforts to model these dynamics were pioneered by the Parton Cascade Model (PCM) [1, 2], which provided a microscopic description of -parton transport through pQCD derived hard scatterings. Since the PCM does not capture soft non-perturbative interactions relevant for bulk dynamics, its application to the description of RHIC and LHC data has been limited. Most contemporary jet–medium interaction models primarily emphasize hard–soft and soft–soft interactions, while direct hard–hard partonic scatterings described by the PCM type models are typically neglected.
In this work, we develop a new implementation of the PCM as an additional component within the JETSCAPE framework to describe interactions among hard partons and provide a more complete description of partonic dynamics. Multijet production is initialized using TRENTO initial conditions, and the subsequent jet evolution is coupled to the SMASH Boltzmann transport model. To describe partonic interactions, the SMASH model is extended to incorporate partonic scattering cross sections. This setup enables the simultaneous treatment of hard–hard scatterings alongside medium-induced radiation and hard–soft and soft–soft interactions already present in the multistage energy-loss framework. We discuss the impact of including hard–hard and multijet interactions on jet quenching observables and outline prospects for systematically improving the description of early-time partonic dynamics.
[1] K. Geiger. Space-time description of ultrarelativistic nuclear collisions in the QCD parton picture. Phys. Rept., 258:237–376, 1995.
[2] Klaus Geiger and Berndt Muller. Dynamics of parton cascades in highly relativistic nuclear collisions. Nucl. Phys. B, 369:600–654, 1992.

Speaker: Chathuranga Sirimanna

PartonCascadePoster.pdf

19:40 Two-particle correlations in p+p collisions with sPHENIX

Collective effects have been observed in a variety of small collision systems; however, their physical origin remains an open question. Extending such studies to lower collision energies than those explored at the LHC is essential for discriminating among competing theoretical explanations. This work presents the first measurement of two-particle correlation functions in proton--proton collisions at $\sqrt{s} = 200$~GeV. The correlation function is measured as a function of relative pseudorapidity and azimuthal angle using electromagnetic calorimeter and silicon tracking data collected by the sPHENIX experiment. Fourier coefficients of the correlation functions are extracted and studied relative to their values in the lowest event-activity class to investigate their evolution with event activity and harmonic order. The data are compared to Pythia simulations, which do not include collective effects. These measurements aim to assess the extent to which the observed correlation patterns can be described by non-collective processes and to test the applicability of non-flow subtraction methods at RHIC energies.

Speaker: Milan Stojanovic (Wayne State University)

MStojanovic_Poster_HP26_v3.pdf

19:40 ϕ Meson Production in Ultra-Peripheral Au+Au Collisions at √sNN = 200 GeV at RHIC

Speaker: Xihe Han

Wednesday 24 June

08:30 → 10:10 Parallels: AI/ML

Convener: Prof. Rithya Kunnawalkam Elayavalli (Vanderbilt University)

08:30 Machine Unlearning and Jet Quenching Physics

The broad spectrum of jet-quenching observables provides a pathway to constraining the microscopic structure of the quark–gluon plasma (QGP) and disentangling the characteristic time and length scales probed by hard partons. Sensitivity to these scales may be essential for understanding the apparent presence of jet quenching in O+O collisions and its absence in p+A systems. Recent studies have increasingly employed machine-learning (ML) techniques to mitigate underlying-event fluctuations and extend jet-quenching measurements to lower transverse momentum. These approaches often report substantial improvements in jet energy estimation prior to full detector response and unfolding.
In this work, we critically examine the physical origin of these reported gains. We propose a targeted suite of closure tests designed to isolate the specific assumptions and correlations exploited by ML-based estimators. Using controlled Monte Carlo studies with PYTHIA and JEWEL, we directly test and falsify several commonly asserted explanations for ML-driven performance improvements. Our results demonstrate that many of the observed gains can be traced to implicit and unvalidated modeling assumptions, rather than to enhanced sensitivity to medium-induced modifications of jets. Furthermore, we show that earlier, analytically motivated background-reduction techniques achieve comparable performance with greater interpretability and robustness, albeit without the same perceived novelty or resource investment.

Speaker: James Lawrence Nagle (University of Colorado Boulder)

nagle_hp_machine_2026_split.pdf

08:50 Identifying Quenched Jets in CMS Using Machine Learning

Jet quenching is a phenomenon in heavy-ion collisions arising from interactions between jets and the quark–gluon plasma (QGP). Modifications of jet-quenching observables result from multiple physical processes, while underlying-event backgrounds and detector effects can significantly influence these observables and must be properly accounted for when identifying quenched jets. We develop a Long Short-Term Memory (LSTM) neural network trained on jet substructure observables, incorporating parton shower history, to predict jet-by-jet quenching levels. Using CMS photon–jet samples, we demonstrate that the LSTM predictions strongly correlate with jet energy loss. This validates the use of LSTM neural network for identifying features sensitive to jet–QGP interactions under realistic experimental conditions, highlighting the potential of sequence-based machine learning approaches for jet-quenching studies.

Speaker: Yilun Wu (Vanderbilt University)

HardProbes2026_v7.pdf

09:10 Apples to Apples in Jet Quenching

Progress in the theoretical understanding of parton branching dynamics within an expanding Quark Gluon Plasma relies on detailed and fair comparisons with experimental data for reconstructed jets. Such comparisons are only meaningful when the computed jet, be it analytically or via event generation, accounts for the complexity of jets reconstructed in the challenging environment of heavy-ion collisions. Jet reconstruction in heavy ion collisions involves a necessarily imperfect subtraction of the large and fluctuating underlying event: reconstructed jets always include underlying event contamination. To identify true jet quenching effects, modifications due to the interaction of the branching partonic system with the Quark Gluon Plasma, we establish a baseline that accounts for possible background contamination on unmodified jets. In practical terms, jet quenching effects are only those not present in jets produced in proton-proton collisions that have been embedded in a realistic heavy-ion background and where subtraction has been carried out analogously to that in the heavy ion case. With this setup, we assess the sensitivity to underlying event of commonly discussed jet quenching observables and its impact on the robustness of Machine Learning studies, aimed at classifying jets according to their degree of modification by the Quark Gluon Plasma, that rely on those observables. We find the discrimination power of a simple Boosted Decision Tree to be robust in the realistic scenario where both medium response and underlying event are present, giving support to portability to the experimental context.

https://doi.org/10.1007/JHEP09(2025)028

Speaker: João A. Gonçalves (LIP - IST)

HP2026.pdf

09:30 Generative ML for heavy-ion mixed-events

The mixed-event techniques are widely used in heavy-ion measurements to estimate uncorrelated backgrounds and instrumental effects for various observables. However, producing large mixed-event samples with sufficient kinematic coverage that require a complete event record (preserving event features as well as particle distributions and their correlations) is computationally expensive, especially as analyses move towards higher precision and more differential measurements with high-luminosity LHC data.

We present a machine-learning approach for mixed-event generation, in which a conditional model learns to produce complete heavy-ion events, from global event features to particle kinematics. The approach adopts and extends Omnilearn, a transformer-based, score-driven foundation model. We demonstrate the model's performance for both O-O collisions (relatively small multiplicity) and central Pb-Pb collisions at the LHC using Argantyr MC simulated events. We benchmark the generator with a broad set of closure checks, including the agreement of event- and particle-level observables such as elliptic flow and two-particle correlations, as well as a suite of key jet and substructure observables. Furthermore, we demonstrate a classifier-based estimator to quantify the fidelity of the generated events. The results show that a compact generative model can produce realistic heavy-ion events, even those with the largest multiplicity, at a fidelity level that makes low-cost mixed-event generation at the LHC a practical goal and a most desired tool. Moreover, it can be used within both purely MC studies and experimental data analysis independent of detector setup.

Speaker: Rita Sadek (Lawrence Berkeley National Lab. (US))

HP2026_rsadek.pdf

09:50 Physics-Informed Symbolic Regression for Quantum Evolution

With the rapid deployment of new machine learning (ML) tools in physics and other fields, the need for physics-informed ML techniques has only grown. Already powerful ML tools can be further optimized for physics applications by incorporating physical symmetries and constraints into the architecture of the ML itself, helping guide the ML toward physically realistic solutions. One such powerful ML tool is symbolic regression (SR), which uses genetic algorithms to evolve symbolic expressions to minimize a loss function. SR is a powerful new tool which has been applied to the study of nonperturbative matrix elements like parton distributions and generalized parton distributions.

We extend this work by demonstrating the application of SR to study not just the parton distributions themselves, but their quantum evolution kernels. We construct a custom loss function for SR which implements the structural form of the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) equations, with an arbitrary expression for the anomalous dimension. Starting from an initial parton distribution function at a fixed scale $Q^2$ as training data, we show that SR can correctly reconstruct the leading-order anomalous dimensions in a closure test. We further demonstrate that a fixed-coupling form of the loss function describes well data generated by fixed-coupling evolution, but not running coupling (and vice versa). This shows that our SR framework provides a systematic test of the predicted DGLAP structure of the data. We further apply this framework directly to HERA reduced cross section data as a proof of principle for the extraction of kernels like the anomalous dimension from experimental data.

Finally, we apply this methodology to study the vacuum DGLAP evolution of jet functions with varying jet radius R. Jets and their interactions with the quark-gluon plasma provide a fertile testing ground, with jet production in vacuum serving as the known DGLAP benchmark. Then SR can be used to extract the form of the medium-modified splitting functions (or equivalent quantities). These results highlight symbolic regression as an interpretable and effective tool for analyzing QCD evolution equations with the potential to both benchmark known theoretical results and experimentally constrain quantities such as the medium modification.

Speaker: Mr Nadeem Altamimi (New Mexico State University)

Physics-Informed Symbolic Regression for Quantum Evolution.pdf

08:30 → 10:10 Parallels: HF and Quarkonia

Convener: Cameron Dean (Massachusetts Inst. of Technology (US))

08:30 Inclusive heavy quarkonium production in lepton-hadron scattering in a joint QED and QCD factorization approach

The Electron–Ion Collider (EIC) will provide an opportunity for precision studies of heavy quarkonium production in electron–proton (ep) and electron-nucleus (eA) collisions. Comparing the production in ep and eA collisions offers a clean and well-controlled experimental environment to study the interactions between a heavy quark pair and nuclear matter and the formation of quarkonia in a nuclear medium. In this talk, we will present the first calculation of heavy quarkonium production in both ep and eA collisions at the EIC energies within a joint QCD and QED factorization framework to treat the collision-induced QCD and QED radiation equally and discuss the role of nuclear medium in exploring how a physical quarkonium is emerged from a produced heavy quark pair. We also systematically extend our calculation to include next-to-leading power contributions in the inverse power expansion of quarkonium transverse momentum, and discuss the matching of our calculations to the fixed order calculations in the NRQCD approach.

Speaker: Jia-Yue Zhang (Jefferson Lab)

ZJY_HP2026.pdf

08:50 Coupled charm and charmonium transport in a strongly coupled quark-gluon plasma

We present a coupled open-charm--charmonium transport framework for the strongly coupled quark--gluon plasma (sQGP) based on a nonperturbative $T$-matrix approach with recent constraints from Wilson-line correlators (WLCs) computed in lattice QCD. For the first time, the same underlying heavy--light interaction and off-shell in-medium spectral functions are used to self-consistently determine both the charm-quark transport coefficients and the charmonium reaction rates. In particular, the charmonium equilibrium limit, a critical transport parameter for regeneration, is evaluated in the presence of broad spectral functions. Charm-quark diffusion is simulated via Langevin dynamics and coupled to a Boltzmann equation describing charmonia kinetics. We demonstrate that this framework recovers the equilibrium limit of the statistical model once charm quarks thermalize, while simultaneously providing a realistic description of off-equilibrium regeneration throughout the fireball evolution. Preliminary results for charmonium yields in Pb--Pb collisions at $\sqrt{s_{\rm NN}} = 5.02~\mathrm{TeV}$ capture the measured centrality and momentum dependence reasonably well. Our work provides a baseline formulation for future quarkonium transport studies in the sQGP.

Speaker: Kaiyu Fu

Hardprobe_2026_KF.pdf

09:10 Quarkonia collectivity in proton-proton, Pb-Pb collisions with ALICE

Quarkonia are key probes of the quark–gluon plasma (QGP). Their azimuthal anisotropies, quantified by flow coefficients, provide insight into the collective behavior and degree of thermalization of heavy quarks in the medium. In particular, the elliptic flow $v_2$ of the $\mathrm{J}/\psi$ meson in Pb–Pb collisions at the LHC has revealed significant collectivity, supporting scenarios of charm-quark thermalization and (re)generation at low transverse momentum. Complementary measurements of the $\Upsilon(1S)$ elliptic flow provide information on the response of beauty quarks, which are expected to couple less strongly with the medium than charm quarks, due to their larger mass. In addition, the observation of collective-like effects in high-multiplicity pp and p-Pb collisions raises questions about the origin of collectivity and the minimal conditions needed for QGP formation.

In this contribution, measurements of quarkonium elliptic flow from small (pp) to large (Pb-Pb) collision systems carried out by ALICE using Run 3 data will be presented. Elliptic flow of $J/\psi$ in Pb-Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.36 TeV using the event-plane, scalar product, and multi-particle cumulants will be discussed, as well as the $v_2$ of $\Upsilon(1S).$ These results will be compared with theoretical models. Finally, new results on $J/\psi$ flow in pp collisions at $\sqrt{s}$ = 13.6 TeV at midrapidity will be presented, further investigating the emergence of collective behavior in high-energy collisions.

Speaker: Magnus Thoegersen (University of Oslo (NO))

MT_HP26_Talk.pdf

MT_HP26_Talk.pptx

09:30 Universal Lindblad equation for in-QGP quarkonium dynamical evolution

Accurate modeling and understanding of quarkonium production in AA collisions requires a formalism that preserves the quantum properties of a microscopic $\bar{Q}Q$ systems while treating the interaction of such pairs with the QGP. The open quantum system approach has recently emerged as one of the most fruitful schemes to meet such requirements. However, the quantum master equations (QME) obtained so far in this approach and currently used to make predictions for the upsilon suppression at RHIC and LHC are derived assuming a strict ordering between the QGP temperature $T$ and the energy gaps ($\Delta E$) of the upsilon bound states. This limits their predictive power as the QGP cooling interpolates between the quantum Brownian regime (QBM), $ T \gtrsim \Delta E $, and the quantum optical regime (QOR), $ \Delta E\gtrsim T$.
In our contribution, we present the limitations affecting the present strategies and next derive a more general non-abelian quantum master equation of the Lindblad type, which does not suffer from these limitations and thus allows to faithfully describe the quantum evolution of the $Q\bar{Q}$ pairs during the whole QGP evolution. This general quantum master equation will be illustrated by various observables pertaining to the quarkonium evolution, such as dissociation rates and spectral densities --- that will be illustrated and shown to smoothly interpolate between the QOR and the QBM regimes --- as well as by specific numerical solutions.

Speaker: Pol-Bernard GOSSIAUX

HP Gossiaux 1609.pdf

09:50 Quarkonia production and flow in light-ions collisions with ALICE

Quarkonium production has long been considered one of the golden probes to study the quark-gluon plasma (QGP). In fact, the early production of heavy quarks ($c\bar{c}$ and $b\bar{b}$) makes quarkonia an ideal tool to investigate the evolution of the hot and dense medium produced in ultra-relativistic heavy-ion collisions. Moreover, at LHC energies the recombination of uncorrelated charm-quark pairs, namely (re)generation, was found to significantly affect charmonium observables, in contrast to the well-known suppression mechanism. On the other hand, measurements in smaller collision systems such as p-Pb have highlighted the possibility to observe QGP-like effects, for instance the larger relative suppression of the $\psi(2\mathrm{S})$ with respect to the $\mathrm{J}/\psi$. In this context, the study of charmonium production in intermediate collision systems, such as light-ion collisions, becomes increasingly interesting, representing an ideal test ground for state-of-the-art theoretical models.

In this contribution, new measurements of charmonium production and elliptic flow are presented using data collected for the first time at the LHC in 2025 in light-ion collisions (oxygen-oxygen, proton-oxygen, and neon-neon). The results are shown exploiting the full ALICE rapidity coverage at mid-rapidity ($|y| < 0.8$) and forward rapidity ($2.5 < y < 4$). Finally, the measurements are compared with existing theoretical models.

Speaker: Liang Dong (University of Science and Technology of China (CN))

HP20260624_Jinjoo_Liang.pdf

08:30 → 10:10 Parallels: Jet

Convener: Mateusz Ploskon (Lawrence Berkeley National Lab. (US))

08:30 Jet Modification in a 3+1D Medium Using the JETSCAPE Framework

We present an extensive study of jet-related observables within the JETSCAPE framework, employing a fully 3+1-dimensional hydrodynamic medium. Event-by-event simulations are performed at LHC and RHIC energies, where longitudinal dynamics and rapidity dependent medium evolution are incorporated to provide the most realistic background for jet propagation. Jet and charged-hadron nuclear modification factors, azimuthal anisotropies and a variety of substructure observables are analyzed using the MATTER and LBT modules embedded in the medium evolution, including initial-state effects such as nuclear shadowing. Medium response is effectuated using the recoil hole formalism. The 3+1D aspect of the simulations allow for realistic extensions of this study beyond Pb-Pb collisions to smaller systems such as O-O and Ne-Ne (and to lower energies), leading to an exploration of how jet observables depend on system size, lifetime, and longitudinal structure. In these smaller and more peripheral systems, where the hadronic phase constitutes a larger fraction of the medium evolution, we investigate the role of partonic energy loss in the hadronic phase. This is carried out by modeling the excited hadrons in the hot hadronic gas with reduced effective parton distributions. These studies assess the sensitivity of jet observables to medium evolution as well as to initial-state and final-state effects across different collision systems, providing a baseline for future experimental comparisons.

Speaker: Yasuki Tachibana (Akita International University)

tachibana_hp2026.pdf

08:50 Bridging soft and hard Bayesian inference in heavy-ion collisions

Bayesian analyses of relativistic heavy-ion collisions have traditionally followed two separate paths: one constraining bulk medium properties via soft-sector observables, and another calibrating jet-quenching parameters using hard probes with a fixed medium. This separation neglects mutual constraints between the two sectors and does not allow a consistent quantification of uncertainties across momentum scales. In this work, the JETSCAPE Collaboration presents a new approach to joint soft–hard Bayesian inference by simultaneously varying parameters from both sectors within a reduced parameter space and focusing on hard-sector observables. By comparing this joint inference with conventional factorized approaches in which soft-sector parameters are fixed, we quantify how neglecting soft-sector uncertainties leads to an underestimation of the total uncertainty in hard-sector parameter extraction. We further demonstrate that hard-sector observables can provide reciprocal constraints on selected bulk medium parameters, illustrating the potential for information flow from hard probes back to the soft sector. The present reduced joint analysis can be combined with projected posteriors from existing soft-only Bayesian calibrations previously performed within the JETSCAPE Collaboration to define a sequential Bayesian inference in a reduced parameter space. Machine-learning-based tools, including emulator techniques and density estimation methods, play a key role in efficiently representing likelihoods and posterior distributions in this setting. This study serves as a proof of concept for a unified framework, establishing a foundation for a fully integrated soft–hard Bayesian calibration in heavy-ion collisions.

Speaker: Lipei Du (UC Berkeley / LBNL)

HP 2026 - L Du.pdf

09:10 Effect of Hadronic Matter on Parton Energy Loss

Jet transport coefficients computed in Hard-Thermal-Loop (HTL) effective theory are applicable at high temperature, while the medium created in heavy-ion collisions, at RHIC and LHC, predominantly samples the region near the QCD transition temperature. The dimensionless transport coefficient $\hat{q}/T^3$, calculated in leading order HTL theory, shows a monotonic rise with decreasing temperature, in spite of all scaled thermodynamic quantities ( $s/T^3 , \varepsilon/T^4$ ) dropping with temperature, and is thus invalid at temperatures near the transition.
We introduce a simple temperature-dependent modification of the in-medium parton distribution through a multiplicative $(1+a/T)$ correction in the dispersion relation, which leads to a transport coefficient $\hat{q}/T^3$ exhibiting a plateau near the transition and a suppression at lower temperatures, consistent with lattice QCD calculations. At high-temperatures, the distribution asymptotically approaches the HTL limit. At lower temperatures, the correction functions as a fugacity, gradually reducing parton populations from the Boltzmann limit. Implemented within the multi-stage MATTER+LBT generators of the JETSCAPE framework, this correction allows the energy loss simulations to be extended beyond the transition temperature, and into the hadronic phase. In this way, we include partonic energy loss in the hadronic phase, where hard partons from the jet, scatter off partons within the excited hadrons of the hadronic phase. The form of the correction, automatically diminishes $\hat{q}/T^3$ at lower temperatures.
The modified distribution increases the contribution from late-time, low-temperature interactions, allowing partonic energy loss to be extended deep into the hadronic phase. When combined with initial state shadowing effects, this framework provides the first simultaneous description of the nuclear modification factor and elliptic anisotropy of jets and leading hadrons over a wide range of centralities from top RHIC to LHC energies, highlighting the role of low-temperature dynamics in hard-probe observables.

[1] R. Datta and A. Majumder, arXiv:2512.23692 [hep-ph].

Speaker: Ritoban Datta (Wayne State University)

RitobanDattaHardProbes2026.pdf

09:30 Jet UE Subtraction and Performance in Au+Au With sPHENIX

The path-length dependence of partonic energy loss is a fundamental property of the Quark-Gluon Plasma that provides critical insights into its transport coefficients and the underlying geometry of the evolving system. Measurements of azimuthal anisotropies for reconstructed jets, characterized by the Fourier coefficients vn, serve as powerful probes of this mechanism. While the second-order coefficient (v$_2$) reflects the average elliptic geometry of the collision, higher-order harmonics such as v$_3$ are sensitive to the path-length variations in the jet trajectories arising from initial-state fluctuations. This talk presents new measurements of jet v$_n$ coefficients using 6.5/nb of Au+Au data at 200 GeV collected in 2025 with the sPHENIX detector at RHIC. These measurements require a detailed understanding of the azimuthally-varying underlying event pedestal as it manifests in the calorimeter system, which must also be characterized and its effects algorithmically removed.

Speaker: Mr Apurva Narde (University of Illinois Urbana-Champaign)

Hard-Probes-26-Talk-Apurva-Narde-v6.pdf

09:50 Investigating the origins of jet quenching with precision measurements of inclusive and semi-inclusive jet modifications with ALICE

Jets are excellent probes to study the properties of the quark-gluon plasma (QGP) produced in heavy-ion collisions, where their modification provides key insights into the medium’s transport properties and dissipation mechanisms. In this talk, we report the measurement of inclusive charged-particle jet suppression and jet azimuthal anisotropy, $v_2$, in Pb–Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.36 TeV. In addition, we also present new measurements of hadron-jet acoplanarity and axes differences in pp collisions at $\sqrt{s}$ = 13.6 TeV and Pb–Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.36 TeV with ALICE. The resulting distributions of nuclear modification factor and $v_2$ probe jet quenching and its path-length dependence. The higher statistical reach of Run 3 data enables high-precision measurements, and comparisons to theoretical calculations provide new insights into the mechanisms underlying jet quenching, including the origin of the acoplanarity broadening observed in hadron-jet distributions measured by ALICE and STAR.

Speaker: Aimeric Landou (University of Liverpool (GB))

20260623_Hard_Probe_JetSuppression_PbPbAndOO_AIMERIC_LANDOU.pdf

08:30 → 10:10 Parallels: nPDF/Saturation/Early

Convener: Alexander Milov (Weizmann Institute of Science (IL))

08:30 Exclusive four pion photoproduction in ultraperipheral Pb-Pb collisions with ALICE

Ultraperipheral collisions (UPCs), where the impact parameter is larger than the sum of radii of two nuclei, provide a clean environment for rare multi-hadron resonances studies. The excited states of $\rho$ meson are predicted by theory, however purely known. The ALICE Collaboration has measured exclusive four-pion photoproduction cross section times branching ratio in UPCs of Pb-Pb at $\sqrt{s_{\rm NN}} = 5.02$~TeV, where single and double resonance structure were considered. However, data suggest two resonance hypothesis.
The upgraded ALICE detector has a new possibility of observing not only four-, but also six-pion states, including decay products of charmonia in Run 3. The data allow for more detailed study of the interplay of resonant and non-resonant contributions in hadronic systems. The invariant mass of these systems is large enough to be considered as a hard probe, while keeping the mass small, hence giving a better sensitivity to phenomenon such as saturation than for example charmonia probes.
In this talk, the newly published result of exclusive four-pion final state from Run 2 will be shown, as well as the ongoing studies of multi-hadron final states from Run 3.

Speaker: Andrea Giovanni Riffero (Creighton University (US))

hp-4pions-agr.pdf

08:50 Measurement of $\gamma \gamma \rightarrow \pi^+ \pi^-$ in Au+Au collisions at STAR using the Entanglement Enabled Spin Interference effect

In ultraperipheral collisions, the invariant mass spectrum of $\pi^+ \pi^-$ pairs is very complex due to the numerous production channels and intermediate states. The most dominant component of this spectrum is $\gamma A \rightarrow \rho^0 (770) \rightarrow \pi^+ \pi^-$ production, and the invariant mass region surrounding the $\rho^0 (770)$ is well-described with the inclusion of photonuclear ($\gamma A$) continuum and $\omega$ meson production. Two-photon processes, like those seen in electron-positron collisions, are also present in ultraperipheral collisions, but the $\gamma \gamma \rightarrow \pi^+ \pi^-$ process has not yet been measured in a nuclear environment due to its low cross section relative to the photonuclear channel. Wavefunction-level interference between the $\gamma \gamma $ and $\gamma A$ channels, referred to as Entanglement Enable Spin Interference (EESI), is expected to produce $A_{1\Delta \phi}$ and $A_{3\Delta \phi}$ signals. This represents a unique method to access the $\gamma \gamma \rightarrow \pi^+ \pi^-$ process in the complex environment of ultraperipheral collisions.

In this talk, the first measurement of EESI between photonuclear and light-by-light production of $\pi^+ \pi^-$ pairs, including the strong EESI signal associated with the $f_2(1270)$ resonance, will be presented. The EESI observables are then used to isolate $\gamma \gamma \rightarrow \pi^+ \pi^-$ in ultraperipheral $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}} = 200$ GeV.

Speaker: Samuel Corey (Ohio State University)

scorey_HP2026_slides_v3.pdf

09:10 Constraining low-x gluon densities with low-p T D0 meson production in ultraperipheral lead-lead collisions at 5.36 TeV with CMS

Speakers: Christopher Mc Ginn (Massachusetts Inst. of Technology (US)), Christopher McGinn (Massachusetts Institute of Technology)

hp2026_CMSUPCD0_CMcGinn_20260624_vFinal.pdf

09:30 Signatures of Initial-State Charge Geometry in Heavy-Ion Collisions

The soft sector of heavy-ion collisions is well described by relativistic hydrodynamics, with the final-state anisotropic flow coefficients $v_n$ arising from quasi-linear response to the initial-state eccentricities $\varepsilon_n$. Based on the principles of long-wavelength dominance in hydrodynamics and rotational symmetry, the initial-state eccentricities serve as “estimators” which predict the response of inclusive particle production to the initial conditions of hydrodynamics. Recently, this initial-state estimator paradigm was extended to the C-odd sector, with the event-by-event flow of net charged particles such as $v_n^{\pi^+} – v_n^{\pi^-}$, produced by quasi-linear response to C-odd measures of the initial-state geometry. In this way, C-odd measures of flow in the soft sector can provide new constraints on the initial-state geometry of conserved charges.

In this work, we generalize the flexible initial-state model TRENTO to deposit charge as well as energy from the colliding nuclei and explore the phenomenology of how different charge geometries influence final-state C-odd flow. We characterize various signatures of the C-odd charge geometry as distinct from the C-even geometry, including both the generation of anisotropy and the reduction of anisotropy due to the charge density. This work contributes to the development of new soft-sector observables sensitive to charge transport, expanding the highly successful C-even paradigm of the initial state to the C-odd sector. By distinguishing between the role of energy versus charge, it can also help to differentiate between quark-initiated and gluon-initiated jets.

Speaker: Matthew Sievert (New Mexico State University)

Sievert_Hard_Probes_2026.pdf

Sievert_Hard_Probes_2026.pptx

10:10 → 10:40 Coffee break

10:40 → 12:00 Parallels: E&M

Conveners: Prof. Charles Gale, Prof. Charles Gale

10:40 Direct Photon Production from Concurrent Minijet-Hydrodynamics Evolution

We study direct photon production within a hybrid minijet-hydrodynamics framework that incorporates initial-state fluctuations and minijet-medium interactions. Using the IP-Glasma + MUSIC + UrQMD framework, and a dedicated photon emission module, we perform a comprehensive analysis of direct photon production. By including minijet effects in the hydrodynamic evolution, we examine the sensitivity of photon yields and elliptic flow to the dynamics of the quark-gluon plasma. Our results demonstrate the significant impact of minijet-medium interactions on the hydrodynamic evolution and on photon production.

Speaker: Mayank Singh (Vanderbilt University)

HP2026_slides_v3.pdf

11:00 Thermal photon production in massless boost-invariant gases

Photons emitted in ultrarelativistic heavy-ion collisions provide penetrating probes of the early-time quark–gluon plasma (QGP), as they interact only weakly with the medium and escape with minimal final-state rescattering. While most measured photons originate from hadronic decays, the direct-photon spectrum cannot be accounted for by prompt production alone and requires a sizable thermal component [1]. In phenomenological applications, thermal photon emission from the QGP is commonly evaluated assuming near-equilibrium dynamics or viscous corrections based on the 14-moment approximation [2]. However, recent kinetic-theory studies demonstrate that, although the energy–momentum tensor is accurately reproduced by fluid dynamics, the underlying single-particle distribution can remain far from equilibrium due to nonhydrodynamic (transient) contributions not constrained by conserved currents [3]. In this work, we quantify how such nonhydrodynamic contributions modify thermal photon production in the QGP within the Forward Scattering Approximation. By comparing photon emission rates obtained from the full kinetic distribution with those computed using 14-moment viscous corrections, we assess the bias induced by standard hydrodynamic truncations and identify the kinematic regimes where early-time photon observables become sensitive to far-from-equilibrium dynamics.

[1] J.-F. Paquet, C. Shen, G. S. Denicol, M. Luzum, B. Schenke, S. Jeon, and C. Gale, Phys. Rev. C 93, 044906 (2016).
[2] C. Shen, J.-F. Paquet, U. Heinz, and C. Gale, Phys. Rev. C 91, 014908 (2015).
[3] C. V. P. de Brito, D. Wagner, G. S. Denicol and D. H. Rischke, arXiv:2411:06267 [nucl-th].

Speaker: Caio Brito (University of Jyväskylä)

deBrito-HP26.pdf

11:20 Direct Photon Yield and Thermal Dielectron Flow in Isobar Collisions at STAR

Thermal dileptons, produced throughout the entire evolution of relativistic heavy-ion collisions, are unique penetrating probes of the hot and dense medium as they escape without being subject to strong interactions. By measuring the transverse momentum distribution of direct virtual photons and elliptic flow ($v_2$) of dileptons emitted from the hot QCD medium, one can extract key properties of the Quark-Gluon Plasma (QGP), such as its temperature and collective expansion, while gaining insights into the mechanisms of thermal radiation.

In this talk, we will present the first measurement of thermal dielectron elliptic flow in isobar collisions (Ru+Ru and Zr+Zr) at $\sqrt{s_{\text{NN}}}$ = 200 GeV, by STAR. Additionally, we extract the direct photon invariant yield via internal conversion method. The presented results will cover direct photon invariant yields and thermal dielectron $v_2$ as a function of mass in different $p_T$ regions. Furthermore, the physics implications of direct virtual photon yield and thermal dielectron $v_2$ will be discussed.

Speaker: xianwen bao

HP2026_Xianwen_Dielectronv2_Final.pdf

11:40 Low $p_T$ direct photon results with PHENIX and their bearing on the direct photon puzzle

Despite decades of theoretical and experimental achievements, a unified description of the space–time evolution of relativistic heavy-ion collisions remains elusive, particularly in the non-perturbative regime of QCD. As penetrating probes, photons provide direct access to all stages of the collision. In particular, the combination of low-transverse-momentum ($p_T$) direct-photon yields and their azimuthally asymmetric emission (flow) provides important constraints on theoretical models. Simultaneous observation of large yields and significant, nearly hadron-like collective flow of low $p_T$ direct photons in Au+Au collisions—often referred to as the “direct photon puzzle”—still lacks a coherent explanation. Closely related is the apparent universality of photon production, that depends only on charged particle multiplicity, but not on the size of the colliding ions, except for the most asymmetric systems. In this talk, we present new measurements of direct-photon flow in Au+Au collisions and of direct-photon yields in Au+Au, Cu+Au, and $^3$He+Au collisions at low $p_T$. Also, we will discuss their impact on our current understanding of the various phases of heavy-ion collisions.

Speaker: Tongzhou Guo

CuAu_photon_Tongzhou.pdf

10:40 → 12:00 Parallels: HF and Quarkonia

Convener: Pol-Bernard GOSSIAUX

10:40 Measurement of production and suppression of $J/\psi$ in correlation with jet activity in $pp$ and Pb+Pb collisions using ATLAS detector

High-energy heavy-ion collisions create conditions under which strongly interacting matter transitions into the deconfined phase of quantum chromodynamics, the quark–gluon plasma (QGP). Yields of charmonia, are observed to be strongly suppressed in heavy-ion collisions relative to proton–proton collisions as a result of their interaction with the QGP. Understanding the mechanisms responsible for this suppression requires a detailed understanding of charmonia production. They may be produced directly in the initial hard scattering and subsequently evolve in the medium, or they may form during parton-shower evolution. To constrain these production mechanisms, it is essential to quantify how charmonia production correlates with jet activity. In this talk, we present a new measurement of $J/\psi$ production for inclusive, jet-isolated, and jet non-isolated $J/\psi$ candidates. The measurement is performed using Pb+Pb and $pp$ collisions at $\sqrt{s_\mathrm{NN}} = 5.02$~TeV recorded by the ATLAS experiment at the LHC, corresponding to integrated luminosities of $1.88$~nb$^{-1}$ and $25$~pb$^{-1}$, respectively. Isolation of charmonia is defined by matching $J/\psi$ candidates to anti-$k_T$ jets with $R = 0.2$ and $p_\mathrm{T} > 20$~GeV, reconstructed without muon signals, allowing the quantification of hard particle activity accompanying the production of $J/\psi$. The $J/\psi$ yields in Pb+Pb, cross sections in pp, and nuclear modification factors are measured for isolated, non-isolated, and inclusive $J/\psi$ up to transverse momenta of $p_\mathrm{T} = 60$~GeV. Non-isolated fractions and non-prompt fractions are reported in both pp and Pb+Pb collisions. Strong $J/\psi$ suppression is observed to persist up to the highest measured $p_\mathrm{T}$, with differences observed between isolated, non-isolated, and inclusive $J/\psi$. These new results provide important constraints on charmonia production mechanisms and their in-medium suppression.

Speakers: Pavel Vana (Charles University (CZ)), Pavel Váňa (Charles University)

Vana_HP26.pdf

11:00 Testing production mechanism of exotic hadrons in nuclear collisions via system size scan

Studies of heavy flavor exotic hadrons such as the χ_c1 (3872) and Tcc states provide crucial insights into the fundamental strong interaction dynamics. An emerging frontier for deciphering their intrinsic structures is to investigate their production in high energy nuclear collisions where a partonic medium is present. The latest experimental measurements from the Large Hadron Collider show an intriguing evolution pattern of the χ_c1 (3872)-to-ψ(2S) yield ratio from proton-proton collisions with increasing multiplicities toward proton-lead and lead-lead collisions. This talk presents a new mechanism of medium-assisted enhancement for the χ_c1 (3872) production, which is deeply rooted in their exotic nature with four constituent quarks/anti-quarks. Using quantitative simulations, this enhancement is shown to compete with the more conventional absorption-induced suppression and result in a highly nontrivial dependence on the size of the colliding systems. Calculations of this provide a quantitative description of all existing data from pp to pA and AA collisions. Predictions are made for the centrality dependence of their production in PbPb collisions. Furthermore, a system size scan is suggested as a crucial test of exotic hadron production mechanism, with model predictions for systems from OO and ArAr to NeNe and XeXe in comparison with PbPb collisions. The talk ends with a discussion on how such measurements may help separate different scenarios for their internal structures.

Speaker: Jinfeng Liao

LIAO_HP2026.pdf

11:20 Enhanced high-$p_T$ $X(3872)$ Production via Correlated $c\bar{c}$ Color-Octet Pairs from Jet Fragmentation

We study the production of the exotic hadron $X(3872)$ in high-energy heavy ion collisions, assuming it to be a $D\bar{D}^{*}$ molecular state.
Motivated by the dominance of the $[q\bar{q}]_{S=1}^{C=8}\otimes[c\bar{c}]_{S=1}^{C=8}$ component in the molecular configuration, we compute the $X(3872)/\psi(2S)$ ratio in pp collisions at $\sqrt{s}=7$ TeV and Pb--Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV, combining a coalescence calculation for the $X(3872)$ spectrum with the experimentally measured $\psi(2S)$ spectrum.
The $c\bar{c}$ color-octet spectrum entering the coalescence calculation is taken as an external input from a pNRQCD calculation, which provides a good description of the experimentally measured $\psi(2S)$ transverse momentum spectrum.
We find that the $X(3872)$ yield obtained in the octet-octet picture is much larger than that from $D\otimes\bar{D}^{*}$ coalescence.
This suggests that the intermediate $c\bar{c}$ color-octet structure can play a more important role in $X(3872)$ production than the mechanism based on independent charm and anticharm quarks.

Speaker: Mr HyeongOck Yun (Yonsei University)

HP2026_HyeongOck_Yun.pdf

11:40 Quarkonia production in heavy-ion collisions with ALICE

Quarkonium production is a direct probe of deconfinement in heavy-ion collisions. For the J/$\psi$, a bound state of a $\rm{c\bar{c}}$ quark pair, (re)generation has been found to be an important production mechanism at LHC energies, providing a clean testing ground to study quarkonium formation and dynamics among various competing production processes. Moreover, the measurement of the quarkonia polarization could provide further insight into the production mechanism and the medium properties from a different perspective.

In this talk, measurements of J/$\psi$ and $\psi(2S)$ production and the spin alignment of the J/$\psi$ as functions of centrality and transverse momentum ($p_{\rm{T}}$) in Pb–Pb collisions at $\sqrt{s_{\rm{NN}}}$= 5.02 TeV will be presented. Furthermore, new preliminary results on the J/$\psi$-to-$\psi(2S)$ production ratio at $\sqrt{s_{\rm{NN}}}$ = 5.36 TeV, obtained with the upgraded ALICE Run 3 detector, will also be shown. All results will be compared with model calculations, and their physics implications will be discussed.

Speaker: Sara Garetti (Université Paris-Saclay (FR))

quarkoniumProd_Garetti.pdf

10:40 → 12:00 Parallels: Jet

Convener: Yeonju Go (Brookhaven National Laboratory (US))

10:40 Probing QGP transport from hydrodynamic attractors to jet wakes

The rapid longitudinal expansion in relativistic heavy-ion collisions drives the quark–gluon plasma toward a universal hydrodynamic attractor at very early times. Assuming approximate boost invariance, we incorporate transverse dynamics and parton evolution by linearizing the Mueller–Israel–Stewart theory around this attractor, leading to a coupled system of ordinary differential equations that describes hydrodynamic perturbations sourced by parton energy loss. The late-time behavior of these perturbations is governed by a nonperturbative transseries, supplemented by jet-induced power-law contributions that dominate asymptotically at late times, with different decay rates in weakly and strongly coupled systems as well as for light and heavy quarks. We demonstrate, via transverse anisotropy, that the jet-induced wake may drive the system away from equilibrium. The transverse structure of the QGP can be analyzed analytically using Green’s functions, a response to the external source whose poles determine the wake modes, including subsonic Kelvin wakes and supersonic shock waves. We show that nonhydrodynamic modes modify Mach-cone formation, and find a lower threshold of the Mach cone formation in the vector (vorticity) channel than in the scalar (temperature) channel. Using vorticity as a proxy for local spin polarization, we predict a nonanalytic behavior of the proposed measurable ''ring observable'' as a function of parton energy. Our findings suggest a new approach to measuring transport coefficients and understanding the thermalization of quark–gluon plasma created in heavy-ion collisions.

Speaker: Xin An (Ghent University)

260624_HP.pdf

11:00 Evidence of medium response in PbPb and the first Z-hadron correlation measurement in pPb collisions

Hard-scattered partons produced in the initial interaction of heavy-ion collisions interact strongly with the QGP through various effects, including jet broadening, medium response, and medium recoil. The production of a Z boson provides a bias-free way to control the energy scale of these hard processes, offering a powerful probe of parton energy loss and the medium response. In this talk, we present measurements of charged-hadron pseudorapidity and azimuthal-angle distributions relative to Z bosons in both PbPb and pPb collisions using CMS. Electroweak bosons do not interact strongly with the medium before decaying. Therefore, reconstructing the Z via its dimuon decay channel and measuring the event-wide hadron angular distribution relative to the Z boson presents a clean method to study medium response away from the outgoing parton.

In PbPb collisions at 5.02 TeV, comparing the hadron distributions to a pp reference and to theoretical models at low transverse momentum reveals the first evidence for medium recoil and hole effects caused by a hard probe. We then extend this approach to pPb collisions at 8.16 TeV. In this smaller collision system, the Z boson probe allows us to access down to unexplored low quark momenta, reducing sensitivity to nPDF effects. We compare the correlations of Z bosons and charged hadrons in pPb to a pp baseline and to the analogous quantities in PbPb. This comparison reveals, for the first time, nuclear modification of the jet and hadronization process in pPb collisions.

Speaker: Kyle Devereaux (Massachusetts Inst. of Technology (US))

Z_Hadron_pPb_HardProbes2026.pdf

11:20 Interferometry probe of the space-time structure of jet-induced medium response

The response of the quark-gluon plasma (QGP) to the energy loss of fast partons is a unique consequence of jet quenching. If this response is hydrodynamic in nature, it generates characteristic space-time structures such as Mach cones and diffusion wakes. However, most existing observables---such as charged-hadron-jet correlations---primarily exploit momentum-space information in inferring the presence of such medium disturbance.

We propose particle interferometry as a direct probe of the space-time structure of the medium response. In particular, we use Hanbury-Brown-Twiss (HBT) correlations of identical particles to access the distortion of the matter distribution at freeze-out induced by jet-medium interactions. Using $\gamma$-jet events in O-O collisions simulated with the CoLBT-hydro model, we compute $\pi^\pm\pi^\pm$ correlation functions following an experimentally established analysis procedure and compare them to a no-jet baseline. We find a clear medium-response signal in the HBT correlation function relative to the baseline, with modifications peaking at finite relative momentum around 0.06 GeV, reflecting its characteristic space-time inhomogeneity. This observable provides an experimentally viable and conceptually direct handle on the space-time structure of the QGP medium response in heavy-ion collisions, thereby opening a new avenue for characterizing the real-time evolution of jet-medium interactions in heavy-ion collisions.

Speaker: Dr Dexing Zhu (Central China Normal University)

HBT-HP2026_dxzhu.pdf

11:40 First observation of the jet-induced diffusion wake in PbPb dijet events

Jet-medium interactions are expected to form a diffusion wake, a medium response to the energy-momentum deposited by a hard-scattered parton, leading to a depletion of particles behind the jet in the quark-gluon plasma. In this talk, we present an experimental study that applies a novel analysis technique to search for a jet-induced diffusion wake using dijet events from PbPb collisions. The effect is quantified via dijet-hadron correlations for different dijet pseudorapidity separations, revealing a clear jet-induced depletion of soft-particle yields opposite to the jet direction. Theoretical models that do not include jet-medium interactions fail to reproduce this behavior. These measurements provide the first unambiguous observation of a jet-induced diffusion wake, offering new insights into jet-medium interactions and the properties of quark-gluon plasma.

Speaker: Mr Raghunath Pradhan (University of Illinois Chicago (US))

Raghunath_HardProbes2026_Final.pdf

10:40 → 12:00 Parallels: nPDF/Saturation/Early

Convener: Dr Gian Michele Innocenti (Massachusetts Inst. of Technology (US))

10:40 Recent results in Ultra-Peripheral collisions at LHCb

Ultra-peripheral collisions offer a unique environment to study pomeron- and photon-induced reactions with heavy nuclei. Such interactions give access to a broad spectrum of final states, from light vector mesons to heavy quarkonia, and probe potentially exotic phenomena. Thanks to its fast and flexible data acquisition system, comprehensive particle identification, and excellent capability to reconstruct very low-$p_T$ particles, LHCb is uniquely well suited to study final states containing leptons, hadrons, or photons. In addition, the HeRSCheL detector enables the detection of far-forward activity, allowing to tag events with nuclear break-up. This contribution presents recent LHCb results from ultra-peripheral heavy-ion collisions and discusses their implications for our understanding of exotic phenomena, the partonic structure of nuclei and hadronization in small systems.

Speaker: James Daniel Brandenburg (Ohio State University (US))

HP2026_jdb_LHCb_UPC_june24.pdf

11:00 J/𝜓 photoproduction and polarization in peripheral Pb-Pb collisions with ALICE

Ultrarelativistic heavy ions generate intense electromagnetic fields that act as a prolific source of high-energy photons, inducing photonuclear reactions. While these processes are typically studied in ultraperipheral collisions (UPCs), where hadronic interactions are suppressed, an unexpected excess of $\mathrm{J}/\psi$ yield at very low transverse momentum ($p_{\mathrm{T}}$) has been observed in peripheral Pb-Pb collisions. This signal is attributed to coherent $\mathrm{J}/\psi$ photoproduction occurring within the nucleus-nucleus (AA) overlap region. This process serves as a unique probe to investigate the interaction between photoproduced states and the fast-expanding quark-gluon plasma (QGP), potentially unveiling new properties of the medium while simultaneously providing a clean experimental signature to constrain the nuclear gluon distribution at low Bjorken-$x$, where gluon saturation effects are expected to emerge. In order to confirm the photoproduction origin of this low-$p_{\mathrm{T}}$ excess, polarization measurements are essential. Based on $s$-channel helicity conservation, the photoproduced quarkonium is expected to retain the transverse polarization of the incoming photon, providing a clear experimental signature to distinguish it from hadronic production.

In this contribution, we present centrality-dependent measurements of coherent $\mathrm{J}/\psi$ photoproduction in peripheral Pb-Pb collisions at both mid- and forward rapidity. Furthermore, we report the first measurement of $\mathrm{J}/\psi$ polarization at forward rapidity. These results are discussed in the context of various theoretical models.

Speaker: Adam Matyja (Polish Academy of Sciences (PL))

HP2026_AMatyja_v2a.pdf

11:20 Probing Gluon Saturation with $J/\psi$ Spin Interference in Photoproduction at STAR

Heavy vector-meson photoproduction is a premier tool for imaging nuclear gluon distributions, traditionally via the momentum-transfer ($t$) dependence of exclusive cross sections. We show that in ultra-peripheral heavy-ion collisions (UPCs) the $J/\psi$ spin/decay angular structure provides a complementary handle for gluon tomography, enabled by the UPC ''two-source'' interferometer and linearly polarized photons.

We present the first evidence of spin-dependent interference in exclusive $J/\psi \to e^+e^-$ photoproduction in ultraperipheral Au+Au ($\sqrt{s_{NN}}=200$ GeV) and isobar (Ru+Ru, Zr+Zr, $\sqrt{s_{NN}}=200$ GeV) collisions at the STAR experiment. A significant negative $\cos(2\phi)$ modulation is observed for the $J/\psi$ at $p_T < 100$ MeV/$c$ with a combined significance exceeding $3\sigma$. Crucially, this sign is opposite to the positive modulation previously observed in $\rho^0 \to \pi^+\pi^-$ photoproduction. This result definitively resolves the ambiguity regarding the interference mechanism, demonstrating that the modulation sign is driven by the specific spin properties of the decay daughters (spin-1/2 fermions vs. spin-0 bosons).

Unlike the soft $\rho^0$ meson, the heavy $J/\psi$ mass scale ($M_{J/\psi} \gg \Lambda_{\mathrm{QCD}}$) allows us to probe the gluon spatial distribution at perturbative scales. We compare the measured modulation strength to Color Glass Condensate (CGC) calculations, showing that the data favor models incorporating linear photon polarization while ruling out scenarios dominated by soft-photon radiation. These findings establish $J/\psi$ spin interference as a novel, hard-scale probe of nuclear gluon structure, providing a critical baseline for future measurements at the EIC.

Speaker: Prithwish Tribedy (Brookhaven National Lab)

prithwish_hp2026_v2.pdf

11:40 Measurements of $J/\psi$ and impact of coincident photon induced processes in ultra-peripheral Pb+Pb collisions at $\sqrt{s_\mathrm{NN}}=5.36$ TeV with the ATLAS detector

In ultra-relativistic heavy-ion collisions, the Lorentz-contracted electromagnetic fields of the ions generate intense quasi-real photon fluxes. These can interact with photons emitted by the oncoming nucleus, or with the nucleus itself, either directly in inelastic processes or diffractively via pomeron exchange. Diffractive photo-nuclear processes can produce exclusive vector mesons that are uniquely sensitive to the spatial and momentum structure of the nuclear parton distribution functions, as well as spatial fluctuations (hot spots). In Run 3, the ATLAS experiment utilized a low-multiplicity track trigger in heavy ions for the first time, allowing the collection of a large sample of events with a few low momentum tracks. A substantial fraction of these are sensitive to di-lepton decays of vector mesons like the $J/\psi$. First results on $J/\psi$ yields, in association with various topologies of forward neutron emission will be presented using the widest continuous rapidity range available at the LHC. The high photon flux also enables the occurrence of multiple photon-induced processes in a single collision. This talk also presents the first measurement of coincident production of $\gamma\gamma \rightarrow \mu^{+}\mu^{-}$ and a $\rho$ meson in UPC Pb+Pb collisions at 5.02 TeV and 5.36 TeV with ATLAS. Scaling of the coincidence $\rho$ meson production rate with neutron topologies di-muon system's properties, such as its mass, are also presented. These results provide tighter constraints on photon fluxes and nuclear charge form factors, as well as insights into nuclear gluon PDFs, beyond those from inclusive $\rho$ meson photo-production.

Speaker: Pawel Rybczynski (AGH University of Krakow (PL))

rybczynski_jpsi_coincident_proc.pdf

12:00 → 13:30 Lunch break

13:30 → 14:50 Parallels: E&M

Convener: Prof. Rithya Kunnawalkam Elayavalli (Vanderbilt University)

13:30 EM-field fluctuations in event-by-event magnetohydrodynamics and their impact on direct-photon yield and flow

We have used our event-by-event relativistic resistive MHD (ebe-RRMHD) framework to uniquely approach the photon $v_2$ puzzle. That puzzle is, no model can reproduce both the photon yield and elliptic flow even with realistic dynamics. Using a realistic electromagnetic (EM) background from our ebe-RRMHD model, we report the EM field impacts on the photon $v_2$ puzzle.

The spectator-generated magnetic field $B_y$ has been proposed by others as a solution to the photon $v_2$ puzzle. We scrutinize that proposal using our RRMHD model [1] that now includes the initial EM field fluctuations. Those fluctuations have two effects: 1) Creation of electric fields with a strength similar to the magnetic. 2) Misalignment between the EM field directional vectors and participant plane. We find that, even under those realistic conditions, the EM fields increase the photon yield and elliptic flow. This suggests that the EM field contributions are necessary to resolve the photon $v_2$ puzzle.

[1] "Investigating effects of the electrical conductivity of QCD matter on charge-dependent directed flow" Phys.Rev.C 112 (2025) 2, 024911; e-Print: 2502.04611 [nucl-th]

Speaker: Nicholas Benoit (Hiroshima University)

HP2026_Benoit.pdf

13:50 Early EM fields in PbPb collisions via their effect on dimuon decays of Z bosons with CMS

In non-central ultrarelativistic heavy-ion collisions, the generation of immense electromagnetic fields has garnered significant interest, particularly regarding their potential effects during the quark-gluon plasma (QGP) phase. Despite extensive studies, the time evolution of these fields within the QGP remains an open question. The Z boson has a very short lifetime and can decay to dimuon final states that can be precisely measured. These properties make it a valuable probe for studying the initial state of heavy ion collisions. It has been proposed that the momentum of muons resulting from a Z decay, and therefore the experimentally observed mass and width of the Z boson, may be modified by the presence of the immense initial-state electromagnetic fields that are thought to be created in heavy ion collisions. Using the CMS experiment, we report the first search for a modification of the observed Z boson mass and width in PbPb collisions at $\sqrt{s_{{\mathrm{NN}}}} = 5.02$ TeV relative to those observed in pp collisions. These measurements are compared to model-dependent theoretical predictions, offering new insights into the interaction between the residual electromagnetic field and the QGP, and helping to further constrain theoretical models.

Speaker: Zheng Huang (University of Illinois Chicago (US))

Zheng_HP2026_Z_EMfield_final_v2.pdf

14:10 Vector meson production and polarisation in pp and OO collisions with ALICE

Polarisation measurements of vector mesons such as $\phi$ and J/$\psi$ have always been of great interest to understand the particle production mechanisms in high-energy collisions. The presence of a large initial angular momentum in non-central heavy-ion collisions can polarise the vector mesons either due to spin-orbital-angular-momentum interaction or by hadronisation from polarised quarks. It has also been conjectured that in heavy-ion collisions vector mesons could be polarised by the strong magnetic field generated in the early phase of the evolution of the system. The $\phi$ and J/$\psi$ meson polarisation in pp collisions could be used as a reference for interpreting the results from light- and heavy-ion collisions.

This talk will present the results of the $\phi$ meson production in pp, OO and Pb--Pb collisions using high-statistics samples collected by ALICE during the LHC Run 3 period. The $\phi$ meson is reconstructed in the dimuon channel in forward rapidity using empirical functions to describe combinatorial background and signal. In addition, the first results on $\phi$ and J/$\psi$ polarisation measurements in pp collisions at $\sqrt{s} = 13.6$ TeV and in OO collisions at $\sqrt{s}_{\rm NN} = 5.36$ TeV will be presented and discussed. The results are compared to previous measurements and to the predictions from various Monte Carlo models.

Speaker: Masahiro Oida (Hiroshima University (JP))

HP26_masahiro_v10.pdf

14:30 Modification of jet shapes and energy-energy correlators in pp, OO, NeNe, and PbPb collisions

Measurements of charged-hadron nuclear modification factors in intermediate systems such as OO and NeNe indicate a moderate size of suppression. However, direct evidence for the complementary medium response has not been demonstrated in these systems. The production of a Z boson provides a bias-free way to control the energy scale of hard processes, offering a powerful probe of parton energy loss and medium-induced modifications of jet structure. This talk will discuss two complementary Z-tagged jet substructure measurements that utilize these clean probes, spanning pp, OO, NeNe, and PbPb collisions with CMS. First, we present the first measurement of the full-event energy-energy correlator (EEC) in PbPb collisions using events tagged with a Z boson. A significant modification of the EEC over a pp reference is observed not only at small to intermediate angular scales, but also in the phase space far from the typical range covered by jet-based EEC, providing new information on how energy is redistributed within and outside jets in the presence of a QGP.

Second, we present the first study of events tagged with an electroweak Z boson in intermediate OO and NeNe systems and examine the particle distribution relative to the Z boson as a Z-tagged jet-shape observable. As the Z boson and its leptonic decay products do not interact strongly, it can serve as a clean tag for the jets recoiling against the Z. Using CMS Run 3 heavy-ion data, we compare charged-particle yields and angular distributions relative to the Z direction in OO and NeNe collisions to pp baselines, and investigate the system-size dependence by comparing them to analogous results in PbPb. This approach minimizes biases from jet selection and provides a clean, system-size-dependent reference for medium modifications and jet quenching. Implication of these Z-tagged jet-shape and EEC studies are also discussed.

Speaker: Preston Crocker White (Vanderbilt University (US))

HP-submit-v2.pdf

13:30 → 14:50 Parallels: HF and Quarkonia

Convener: Dr Ivan Vitev

13:30 Bottomonium production & modification in small systems: disentangling cold and hot nuclear effects in $p+\mathrm{Pb}$ collisions

Measurements of bottomonium [$\Upsilon$(1S,2S,3S)] production in $p+\mathrm{Pb}$ collisions at the LHC show a pronounced state dependence that cannot be described by cold nuclear matter (CNM) effects alone. We present a unified study of $\Upsilon$($n$S) production in minimum-bias $p+\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=5.02$ and 8.16 TeV that incorporates both CNM and final-state hot medium effects. The CNM contributions are modeled through nuclear parton distribution functions (EPPS21), coherent energy loss, and transverse-momentum broadening. Final-state interactions are evaluated by propagating the bottomonia through a short-lived quark-gluon plasma where the space-time evolution is described by 3+1D quasiparticle anisotropic hydrodynamics. We assess bottomonium transport in the QGP using two complementary approaches implemented in the same hydrodynamic background. The first is an open quantum systems formulation based on a Lindblad equation derived in pNRQCD and solved using quantum trajectories. The second solves a semiclassical kinetic rate equation with dissociation and regeneration, employing both perturbative and lattice-QCD-constrained nonperturbative reaction rates. We compute the nuclear modification factors $R_{pA}(y,p_T)$ including feed-down contributions and compare to ALICE, ATLAS, CMS, and LHCb data.
The results quantify the relative importance of CNM effects, primordial suppression, and regeneration in small systems, and identify observables sensitive to genuine quantum effects in bottomonium transport.

Speaker: Mr Sabin Thapa

HardProbes2026_Sabin.pdf

HardProbes2026_Sabin.pdf

13:50 Charmonium production and modification in $p+\mathrm{Pb}$ and $d+\mathrm{Au}$ collisions

We present a systematic study of charmonium production in small collision systems, focusing on $p+{\rm Pb}$ collisions at $\sqrt{s_{NN}}=5.02$ and $8.16$~TeV and ${\rm d} +{\rm Au}$ collisions at $\sqrt{s_{NN}}=200$~GeV [1]. As in our previous work [2,3], we quantify the relative contributions of cold nuclear matter (CNM) effects and final-state hot QCD interactions with hot QCD matter in a unified framework. The CNM effects are described using the EPPS21 nuclear modifications of parton distribution functions with coherent energy loss and transverse momentum broadening. Final-state effects are evaluated within the space-time evolution of the medium obtained from $3{+}1$D viscous anisotropic hydrodynamics. The charmonium evolution in the medium is described by a semi-classical kinetic rate equation with temperature-dependent inelastic reaction rates evaluated along trajectories through the evolving background. The hot matter contribution incorporates both dissociation and regeneration. The nuclear modification factors are computed as functions of rapidity, transverse momentum, and centrality, including excited state feed down. The results are compared with measurements from RHIC and the LHC.

[1] S. Thapa, R. Vogt, B. Wu, and R. Rapp, (In Preparation).

[2] M. Strickland, S. Thapa, and R. Vogt, Phys. Rev. D 109, 096016 (2024), arXiv:2401.16704 [nucl-th].

[3] S. Thapa, B. Wu, R. Vogt, and R. Rapp, (2025), arXiv:2510.03456 [nucl-th].

This work was supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics through the Topical Collaboration in Nuclear Theory on Heavy-Flavor Theory (HEFTY) for QCD Matter under contract DE-SC0023547. R.V. was supported by the U.S. Department of Energy by LLNL under contract DE-AC52-07NA27344.

Speaker: Ramona Vogt

HP_RV_26.pdf

14:10 Evidence of sequential Y meson suppression in NeNe and OO collisions in CMS

Speakers: Austin Alan Baty (University of Illinois Chicago), Austin Baty (University of Illinois Chicago)

Baty_Upsilons_OO_NeNe_pPb_HardProbes2026_v2.pdf

14:30 Insights into Hard–Soft QCD Correlations from Multiplicity-Dependent Charmonium Production in p+Au Collisions at PHENIX

We present new PHENIX measurements of the event-activity dependence of
charmonium production in p+Au collisions at \sqrt{s_{NN}}=200 GeV. These
measurements provide a sensitive probe of the interplay between hard
production processes and the soft particle production that characterizes
the underlying event in small collision systems. In particular, they offer
constraints on possible contributions from multi-parton interactions,
long-range partonic correlations, nuclear-modified parton dynamics, and
final-state effects in asymmetric nuclear collisions at RHIC.

The PHENIX detector provides a unique experimental configuration for this
study, with spectrometer coverage at forward, mid-, and backward
pseudorapidities. The forward and backward muon arms enable measurements
of J/\psi production in different Bjorken-x regimes of the p+Au collision
system, while independent event-activity estimators at separated
pseudorapidities allow potential autocorrelation biases between the
charmonium signal and the multiplicity measurement to be reduced. This
approach builds on lessons from previous p+p studies and provides a
cleaner experimental handle on correlations between hard probes and global event
activity. We report the multiplicity dependence of J/\psi production across
rapidity and discuss the observed trends in the context of QCD dynamics in
small systems. The results provide new insight into the mechanisms
connecting charmonium production, event activity, and nuclear effects in
p+Au collisions at RHIC.

Speaker: Ming Xiong Liu (Los Alamos National Laboratory)

PHENIX-JPsi-Multiplicity-HP2026-Liu-final.pdf

13:30 → 14:50 Parallels: Jet

Convener: Krishna Rajagopal (Massachusetts Inst. of Technology (US))

13:30 QCD in-medium splitting kernels at full colour and exact kinematics

The building block of jet quenching calculations is the differential matrix-element to radiate a gluon off a highly-energetic parton in a dense QCD medium. Analytical expressions were presented more than 30 years ago in the pioneering work of BDMPS-Z. However, exact solutions have remained elusive, thus hampering the precision of jet quenching phenomenology.

We present the first calculation of QCD in-medium splitting kernels which accounts for the exact transverse kinematics of the partons, finite-$N_c$ corrections and a realistic medium potential, providing solutions across the entire phenomenologically relevant phase space. Building on [1], we formulate the problem as a set of tractable evolution equations and solve them using an efficient and stable numerical method based on the Faber expansion of the time-evolution propagator [2]. We analyse the applicability of the large-$N_c$ limit and demonstrate the breakdown of the commonly employed straight-line approximation. As a phenomenological application, we compute in-medium energy–energy correlators (EECs) at LHC kinematics and quantify the impact of full transverse dynamics and improved medium potentials in jet substructure observables.

[1] JHEP 09 (2023) 049
[2] Comput. Phys. 216 (2006) 391-402

Speaker: Marco Leitão (IPhT-Saclay & LIP-Lisbon)

presentation.pdf

13:50 Hamiltonian real-time quantum evolution of particles in the Glasma

We present a new formalism to compute the quantum evolution of a high-energy quark inside the Glasma phase of a heavy-ion collision. We employ a basis representation to describe the quark state and evolve it by solving the Schrödinger equation within the formalism of light front quantum field theory. We show that, by neglecting quantum corrections like the emission or absorption of gluons by the quark, our formalism reduces to the results obtained by considering the quark as a classical probe particle. We obtain results for the momentum broadening of the particle, and compare the physical gauge-invariant kinetic momentum of the particle and the gauge-dependent canonical momentum, conjugated to coordinate space. We also pay attention to the anisotropies in momentum broadening between the longitudinal and transverse directions with respect to the beam. This framework provides a path to investigating quantum effects in the pre-equilibrium stage, in particular the size of energy loss.

Speaker: Carlos Lamas (IGFAE-USC)

Slides_HP_Nashvile.pdf

14:10 How the nonequilibrium initial stages influence medium-induced radiation

One of the central open questions in heavy-ion collisions is how the initially far-from-equilibrium plasma of deconfined quarks and gluons evolves toward local thermal equilibrium, a process known as hydrodynamization. Despite its importance, direct experimental signatures of this early pre-equilibrium stage remain elusive. Hard probes, such as jets, produced at very early times, offer a promising window into these dynamics. In this talk, I present results for the medium-induced gluon radiation from an energetic parton traversing the quark-gluon plasma, whose nonequilibrium time evolution is simulated within QCD kinetic theory. I show that the resulting radiation pattern deviates significantly from expectations based solely on thermal emission, providing new insights into the non-equilibrium nature of the medium. These differences can be linked to the underlying bottom-up equilibration process of the plasma, which consists of under- and overoccupied stages, and whose imprints are visible in the spectrum.

Speaker: Florian Lindenbauer (MIT Center for Theoretical Physics - a Leinweber Institute)

2026-06_Hard_Probes_Nashville.pdf

14:30 Causality of jets coupled to relativistic viscous hydrodynamic simulations

Jets produced in high-energy nuclear collisions interact with the medium, transferring energy and momentum into it, which generates a non-trivial hydrodynamic response. In this work, we investigate these jet–medium interactions using the newly developed NuclearConfectionery multi-stage simulation framework [1], with CCAKE 2.0 as its hydrodynamic core. Within this framework, CCAKE 2.0 provides a fully relativistic viscous hydrodynamic description of the medium, enabling 3+1-dimensional evolution with all conserved charges (baryon number, strangeness, and electric charge). Jet effects are incorporated through source terms in the conservation equations, allowing us to study the impact of jets on the medium’s dynamical evolution. Here we study how jets with different initial energies, as well as different types of energy loss model,s affect the causality constraints. We discuss implications for diffusion wake simulations.

[1] Pala et al, 2511.22852 [nucl-th]

Speaker: Kevin P. Pala

hardprobes_kp.key

hardprobes_kp.pdf

hardprobes_kp.pptx

13:30 → 14:50 Parallels: nPDF/Saturation/Early

Conveners: Sangyong Jeon, Sangyong Jeon

13:30 Unified description of longitudinal and transverse parton dynamics in cold nuclear matter

Precision tomography of nuclear matter requires a unified description of three-dimensional in-medium parton evolution, including both longitudinal momentum evolution and transverse-momentum broadening. Importantly, for reaction in a finite-size nuclei, transverse-momentum–dependent (TMD) dynamics and Landau–Pomeranchuk–Migdal interference must be treated consistently. Using SCET with Glauber gluons (SCET${}_{\rm G}$), we derive a medium-induced 3D evolution equation in cold nuclear matter. We show that a BFKL-type rapidity-renormalization-group improvement of the collision kernel, together with an RG evolution of impact-parameter-dependent energy loss, is essential for a simultaneous description of both longitudinal and TMD observables using a consistent set of cold-nuclear-matter parameters. We apply this framework to semi-inclusive DIS and Drell–Yan on nuclear targets. Based on Ref. [1] and new results for SIDIS on nuclei, we present predictions for EIC and EicC kinematics, demonstrating the role of combined collinear and TMD measurements as precision probes of cold nuclear matter.

[1] Weiyao Ke, John Terry, Ivan Vitev JHEP02(2025)102 and works in preparation.

Speaker: Prof. Weiyao Ke (Central China Normal University)

Weiyao-Ke-HP26-v3.pdf

13:50 Revealing the Cronin effect through Drell Yan in p-A collisions

An enhancement in the transverse momentum distribution of Drell-Yan pairs was recently observed in $p$-$Au$ collisions, in the proton going direction, by the PHENIX experiment at RHIC. This observation, along with the absence of any enhancement in the nucleus going direction is consistent with the Cronin effect, and with the observed enhancement in a series of fixed target experiments at Fermilab, carried out over several decades (R209, E288, E537, E605, E615, E772, E866, NuSea etc.). Hard partons from the proton undergo pre-scattering in a large nucleus, prior to the hard process where a dilepton pair with mass $Q$ and transverse momentum $q_T$ is formed. While earlier studies focussed on the angular distribution, the energy loss of low $q_T$ Drell-Yan pairs, as well as the $q_T$ distribution in the collinear limit [1], we specifically focus on large transverse momentum pairs, where $q_T \sim Q$, using factorized Transverse Momentum Dependent Parton Distribution Functions (TMDPDFs). From the hundreds of Feynman diagrams contributing at Next-to-Leading Order and Next-to-Leading-Twist (NLO-NLT), for the case of arbitrary $q_T$, we show that only about 24 diagrams dominate in the limit where $q_T \gg \Lambda_{QCD}$. None of these diagrams involve off-forward distributions, allowing for a constrained evaluation using known parameterizations of TMDPDFs. Evaluating these diagrams, we illustrate the dependence of the differential spectrum, as a function of $q_T$, on the excess transverse momentum imparted by the pre-scattering. Comparing numerical results to data, we illustrate, for the first time, the possibility of momentum fraction ($x$) and intrinsic transverse momentum ($k_T$) dependence in nuclear shadowing. These contributions are also present in hadron and jet production in $p$-$A$ collisions, where convolution with final state interactions obfuscates the actual effect of initial state scattering.

Speaker: Abhijit Majumder (Wayne State University)

Majumder_Drell_Yan.pdf

14:10 Towards a Unified Picture of Nuclear QCD: Mapping the Transition from High-Twist to Color Glass Condensate Dynamics

The exploration of the high-energy nuclear landscape necessitates complementary theoretical frameworks to describe the transition from dilute to dense partonic systems. Two established paradigms for perturbative QCD multiple scatterings in nuclei are the Color Glass Condensate (CGC) effective theory, applicable in the high-density regime, and the collinear factorization-based high-twist (HT) expansion, which is valid when parton densities are comparatively dilute. While their domains of validity are distinct, a unified description of their interplay remains an outstanding question.

In this work (PRL 135, 032301 (2025) and PRD 112, 014029 (2025)), we establish, for the first time at the level of a physical observable, the precise correspondence and matching between the CGC and HT formalisms in their overlapping kinematic region. Using direct photon production in proton-nucleus collisions as a concrete and calculable example, we demonstrate that a consistent matching requires the CGC calculation to be performed beyond the standard eikonal (shock-wave) approximation. Crucially, the inclusion of the sub-eikonal longitudinal momentum phase—which encodes the Landau-Pomeranchuk-Migdal interference effect and mediates the transition between coherent and incoherent scatterings—is shown to be essential. The techniques developed here can be extended to other processes in electron-nucleus and proton-nucleus collisions, paving the way for mapping out a comprehensive phase diagram of parton density in nuclear media.

Speaker: Yu Fu (Duke university)

HP2026_HT_CGC_YuFu.pdf

14:30 Exploring Cold Nuclear Matter through Forward $\pi^{0}$ Production in $p+$A Collisions at STAR

The community is motivated by intriguing indications of parton saturation observed at RHIC and LHC, as well as by the large uncertainties in nuclear parton distribution functions (nPDFs) at small parton momentum fractions ($x$) and low-to-moderate $Q^{2}$. The unique photon detection capabilities of the STAR Forward Meson Spectrometer (FMS), covering the pseudorapidity range $2.6 < \eta < 4$, make forward neutral pion ($\pi^{0}$) production an effective probe of partonic dynamics at small $x$ and moderate energies in proton--nucleus ($p+$A) collisions.

In this talk, we present the first measurement of the forward $\pi^{0}$ nuclear modification factor, $R_{\text{pA}}$, where the $\pi^{0}$ transverse momentum spectra measured in proton--gold ($p+$Au) and proton--aluminum ($p+$Al) collisions are compared to those in proton--proton ($p$$+$$p$) collisions. The analysis is performed using data recorded by the STAR experiment in 2015 at $\sqrt{s_{\text{NN}}} = 200~\text{GeV}$. This measurement will provide valuable constraints on nPDFs, offer insight into the onset of gluon saturation, and serve as a critical reference for understanding parton dynamics in nuclei.

Speaker: Dener De Souza Lemos (UNESP - Universidade Estadual Paulista (BR))

DSLemos_HardProbes2026_Pi0RpA-v4.pdf

14:50 → 15:20 Coffee break

15:20 → 16:20 Parallels: E&M

Convener: Chun Shen (Wayne State University)

15:20 Photon production in medium-modified jets: phenomenology and precision

Photons and electroweak probes are an important class of observables for quantifying hard processes in the quark-gluon plasma. While previous efforts have used prompt photons to perform jet coincidence measurements, here we suggest a strategy of identifying photons within jets and compute relevant observables. Direct photos emitted within QCD jets are a unique tool for studying the space-time evolution and the perturbative structure of the parton shower in both pp collisions [1,2] and in heavy-ions [3,4]. Since photons do not interact with the QGP, they provide us with a clean picture of the fragmentation process.

In this talk we will present the results for the leading-order, fully differential photon spectrum in the presence of a medium [4], computed within the opacity and improved opacity expansions [5], and highlight the role of photon isolation criteria to being sensitive to two distinct medium-induced processes: a) the broadening of quarks in the shower, and b) genuine, medium-induced emissions of hard photons in the QGP. Additionally, we will discuss the advancements in computing 𝓞$(α_{EM} α_s )$ corrections to this spectrum [6] by allowing for photon emissions during the medium-induced turbulent cascade that leads to strong jet quenching effects [7]. Finally, we will present the potential challenges one has to face when going to higher-loop computations to achieve NLO precision when a background gauge field is present.

[1] E. Hall, and J. Thaler "Photon isolation and jet substructure", JHEP 09 (2018) 164; arXiv:1805.11622 [hep-ph]
[2] T. Becher, S. Favrod, and X. Xu "QCD anatomy of photon isolation", JHEP 01 (2023) 005; arXiv:2208.01554 [hep-ph]
[3] U.A. Wiedemann, and M. Gyulassy " Transverse momentum dependence of the Landau-Pomeranchuk-Migdal effect", Nucl. Phys. B 560 (1999) 345; arXiv:hep-ph/9906257 [hep-ph]
[4] A. Falcao, and K. Tywoniuk (in preparation)
[5] J. Barata, Y. Mehtar-Tani, A. Soto-Ontoso, and K. Tywoniuk " Medium-induced radiative kernel with the Improved Opacity Expansion" JHEP 09 (2021) 153; arXiv:2106.07402 [hep-ph]
[6] N. Neher, and K. Tywoniuk (in preparation)
[7] E. Blanco, K. Kutak, W. Placzek, M. Rohrmoser, and K. Tywoniuk "System of evolution equations for quark and gluon jet quenching with broadening", Eur. Phys. J. C 82 (2022) 4, 355; arXiv:2109.05918 [hep-ph]

Speaker: Narcis Neher

HP_Nashville_2026_Neher.pdf

15:40 Electromagnetic radiation from jet-medium interactions and the dynamical evolution of quark flavors in heavy-ion collisions

A comprehensive calculation of electromagnetic radiation from jet-medium interactions at $O(e^2g^2_s)$ and at next-to-leading twist is presented, incorporating both Glauber quark and Glauber gluon scatterings with the nuclear medium [1]. Two types of scattering kernels are computed giving the following final states: (i) a real photon and a real quark, as well as (ii) a real photon and a real gluon. Moreover, this calculation accounts for both transverse and longitudinal momentum exchanges with the nuclear medium and is directly sensitive to transverse-momentum-dependent quark and gluon parton distribution functions of nuclear matter. Together, the Glauber gluon and quark contributions to scattering-induced stimulated photon emission enables to use jet-medium photons to study how the medium in heavy-ion collisions transitions from the early-time Glasma dynamics to the QGP. As electromagnetic radiation is less affected by hadronization effects, photons have an increased sensitivity to flavor composition dynamics in heavy-ion collisions. Both the Glauber quark and gluon contributions to photon production in jets are being implemented within a new Monte Carlo event generator called JETSMITH (Jet and Electromagnetic Tomography in Strongly interacting Medium Inferred Through Higher-twist), and first results of this event generator will be presented at this conference. Finally, we will explore how to extend this calculation to include off-equilibrium effects, starting with shear viscous pressures present in a dissipative QGP fluid.

References:
[1] A. Kumar and G. Vujanovic, Phys. Rev. C 112, 025204 (2025)

Speaker: Prof. Gojko Vujanovic (University of Regina)

HP26_GV_v2.5.pdf

16:00 sPHENIX measurement of isolated prompt photon production in p+p collisions at 200 GeV

High transverse momentum (p$_T$) isolated prompt photons provide stringent tests of perturbative QCD and sensitivity to the gluon parton distribution function. During the 2024 data taking, sPHENIX at RHIC recorded 107/pb of p+p collisions at a center-of-mass energy of 200 GeV using efficient high-p$_T$ photon triggers. As a next-generation collider detector, sPHENIX combines large-acceptance electromagnetic (EMCal) and hadronic (HCal) calorimeters with full azimuthal coverage and more than two units in pseudorapidity, together with a high-rate trigger and data acquisition system. This talk presents the isolated prompt photon production cross section in p+p collisions. For the first time at RHIC, photon isolation is defined using the combined EMCal and HCal systems, enabling a full accounting of the energy deposited in the isolation cone. This measurement serves as a standard candle for sPHENIX calorimeter performance and establishes an essential pQCD baseline for isolated photon and photon+jet measurements in Au+Au and O+O collisions. The measured cross section is compared with Monte Carlo event generators and next-to-leading-order pQCD calculations, as well as previous measurements of photon production at RHIC.

Speaker: Justin Bennett (University of Illinois Urbana-Champaign)

HP26_EMsession_JustinBennett_6_24_26.pdf

15:20 → 16:20 Parallels: HF and Quarkonia

Convener: Anthony Frawley

15:20 Charm and beauty production in pp collisions with ALICE

Heavy quarks, namely charm and beauty, are predominantly produced in initial hard partonic scatterings and therefore provide a powerful probe to test perturbative quantum chromodynamics (pQCD). Owing to their large masses, their production can be calculated within the pQCD framework, while their hadronisation offers unique sensitivity to non-perturbative QCD dynamics. Measurements performed by the ALICE Collaboration in Run 2 have shown that charm-baryon production in proton–proton (pp) collisions cannot be described by a universal hadronisation mechanism, as evidenced by the enhanced charm baryon-to-meson ratios compared to expectations from fragmentation-based models. These observations motivate further studies with improved detector performance and significantly increased statistics.

In this contribution, new measurements based on ALICE Run 3 pp data at $\sqrt{s}=13.6$ TeV are presented. Updated measurements of non-strange D-meson production are shown. In addition, the charmed-strange-baryon $\Xi_{\mathrm{c}}^{+}$ is measured for the first time with ALICE via the $\mathrm{pK\pi}$ decay channel, enabled by the improved tracking and vertexing capabilities. Using ALICE Run 3 data, the role of event activity in charm hadronisation is further explored, and the multiplicity dependence of the $\Lambda_\mathrm{c}^{+}/\mathrm D^{0}$ ratio is presented.

The production of beauty hadrons is studied as a complementary probe of QCD dynamics at higher mass scales. The improved vertex resolution achieved in Run 3 enables the direct reconstruction of beauty hadrons, and the first measurement of the $\mathrm B^{0}$-meson production cross section with ALICE in pp collisions is presented.

Speaker: Jianhui Zhu (Fudan University)

20260624_HardProbes_JianhuiZhu_v6.pdf

15:40 Heavy flavour production from pp, light- and heavy-ion collisions at LHCb

Heavy quarks are powerful probes of both hot and cold nuclear effects in high-energy nuclear collisions. After their production in the collision initial stage, they experience QGP formation and interact with the produced medium through its evolution. The LHCb experiment is uniquely well-suited to studying heavy-flavor production in a variety of systems. During Run 3, LHCb collected its first samples of $p$O, OO, and NeNe collisions during the summer of 2025, and a sample of PbPb collisions with an extended centrality coverage and increased luminosity compared to that from Run 2. In this contribution, first results of open heavy-flavour production in these collisions systems will be presented.

Speaker: Jiazhao Lin (Indiana University (US))

HP2026_v3.pdf

16:00 Exploring System-Size and Energy Dependence of J/$\psi$ production with the STAR experiment

The suppression of quarkonium production in heavy-ion collisions has long been rec6 ognized as a key signature of QGP formation, reflecting the medium’s temperature and color-screening properties. However, interpreting the observed nuclear modification factor ($R_{AA}$) remains challenging due to the interplay between hot-medium effects (dissociation and regeneration) and cold nuclear matter effects. Systematic measurements across different collision systems and energies are therefore essential to disentangle these contributions and deepen our understanding of QGP properties. In this talk, we present measurements of the J/$\psi$ $R_{AA}$ as a function of centrality and transverse momentum in O+O collisions at $\sqrt{s_{NN}}$ = 200 GeV, and in Au+Au collisions at $\sqrt{s_{NN}}$ = 14.6–27 GeV collected during the RHIC BES-II program. The O+O data probes a unique regime in system size, bridging small (p+p, p+Au) and large (Au+Au, U+U) collisions. These measurements provide crucial insight into the onset of QGP formation and the nuclear properties across system size and energy. We further discuss the energy dependence of J/$\psi$ $R_{AA}$ from RHIC to LHC energies and compare the results with theoretical model calculations.

Speaker: Frank Geurts (Rice University (US))

HP2026_wei.pdf

15:20 → 16:20 Parallels: Jet

Convener: Christine Nattrass (University of Tennessee (US))

15:20 Probing medium properties with jet energy flow modification in heavy-ion collisions with ALICE

Jets serve as well calibrated, multi-scale probes of the quark–gluon plasma (QGP) produced in high-energy heavy-ion collisions. The jet energy flow, an infrared- and collinear-safe observable, characterizes how the energy inside a reconstructed jet is distributed as a function of angle (radius) from the jet axis and is directly sensitive to medium-induced modifications of parton shower evolution. These modifications arise from the interplay between medium-induced emissions which redistribute the energy to larger angles, and the larger suppression of wide jets due to color-coherence effects. The jet energy flow observable provides an event-by-event measure of these modifications.

The ALICE Collaboration presents the first measurement of jet energy flow in heavy-ion collisions. The measurement is performed for inclusive-charged jets in Pb--Pb collisions in the transverse-momentum interval $60–80~\mathrm{GeV}/c$, with a pp reference used to investigate medium-induced modifications. The results are compared to Monte-Carlo event generators and predictions, including JETSCAPE and the Hybrid Model, providing insight into QCD dynamics across different collision systems. These measurements place new constraints on models of jet–medium interactions and demonstrate the sensitivity of the jet energy flow observables to the microscopic mechanisms of parton energy loss in the QGP.

Speaker: Preeti Dhankher Lesser (Nikhef National institute for subatomic physics (NL))

PDhankher_JEF_HP26.pdf

15:40 Precise Measurement of the Jet Energy Scale Using In Situ Methods in p+p Collisions at √s=200 GeV at sPHENIX

The response of the sPHENIX calorimeter system to jets is calibrated using in situ techniques in p+p collisions at sqrt(s) = 200 GeV provided by the Relativistic Heavy Ion Collider. Events in which a jet recoils against a reference object with an independently-determined energy scale are studied, comprising photon-jet and multijet processes. The response in data is compared to that in Monte Carlo simulation. Data-to-Monte Carlo jet energy scale ratios are examined and final corrections are derived as a function of jet transverse momentum and jet radius parameter. The corrections are 1-2% with uncertainties ranging from 3-4% over the jet transverse momentum range 10-60 GeV. These constraints are critical for the precision sPHENIX jet physics program in p+p and heavy-ion collisions.

Speaker: Sam Liechty

HardProbes_insitu_JES

16:00 sPHENIX measurements of dijet correlations in p+p and Au+Au collisions at 200 GeV

Measurements of dijet kinematic correlations in heavy ion collisions have historically provided significant insights into the mechanisms of jet quenching in the Quark-Gluon Plasma. At RHIC energies, medium-induced modifications of the dijet $p_T$ asymmetries and angular decorrelations are expected to be enhanced compared to the LHC, due to the tighter initial kinematic correlations and much lower parton energies which are closer to QGP medium scales. This presentation details measurements of dijet momentum balance $x_J$ and azimuthal correlations in Au+Au and p+p collisions at 200 GeV, the first such measurements at RHIC using a full electromagnetic and hadronic calorimeter system. In p+p collisions, the measurement is performed for a variety of cone sizes and provides a critical benchmark of the Monte Carlo event generators used for the vacuum physics in many theoretical approaches. The dijet asymmetry in Au+Au collisions is observed to be strongly modified in a centrality-differential way and is compared to a variety of heavy-ion event generators and modern theoretical calculations.

Speaker: Daniel Lis

hp2026_dlis_finaldraft.pdf

15:20 → 16:20 Parallels: nPDF/Saturation/Early

Convener: Ramona Vogt

15:20 Probing nuclear structure at LHCb

With its unique forward geometry, the LHCb detector provides unprecedented access to very low Bjorken-$x$ inside the nucleon. Its excellent momentum resolution, vertex reconstruction, and particle identification enable precision measurements of charged and neutral light hadrons, as well as rarer probes such as heavy quarks, down to very low transverse momentum. These data provide unique constraints on nuclear parton distributions. This contribution will discuss recent LHCb measurements sensitive to the structure of nucleons, and discuss their impact on global analyses of nuclear parton distribution functions.

Speaker: Thomas Boettcher (Indiana University (US))

boettcher_HP2026_260624.pdf

15:40 Top quark and UPC jet probes of nuclear matter with ATLAS

Top quarks produced in heavy-ion collisions are expected to be attractive candidates for probing the quark-gluon plasma, developing new information about the time structure strongly interacting matter, and probing nuclear parton distribution functions (nPDFs). This talk presents the observation of top-quark production in lead–lead (Pb+Pb) collisions at 5.02 TeV with the ATLAS experiment at the LHC. The results include data collected in 2015 and 2018, with an integrated luminosity of $1.9~\mathrm{nb}^{-1}$. The cross-sections are compared to theoretical predictions based on various nPDF sets. Complementary to these measurements, jet production in ultra-peripheral Pb+Pb collisions at 5.02 TeV has been studied using ATLAS data. In these events, high-energy photons emitted by one nucleus interact with partons in the other, providing a clean electromagnetic probe of nuclear structure. By requiring no forward neutron emission, these events select two processes: peripheral photonuclear jet production and diffractive jet photoproduction. Measurements of the ratio of peripheral to inclusive jet photoproduction allow for the observation of impact parameter dependent nPDF modifications. Additionally, first measurements are performed of coherent diffractive jet photoproduction in photonuclear UPCs, which are sensitive to factorization-breaking effects and provide direct input for constraining existing models.

Speaker: Patrycja Anna Potepa (AGH University of Krakow (PL))

HP2026-Potepa.pdf

16:00 Measurement of Top quark pair production in Run3 PbPb collisions at 5.36 TeV with CMS

The production of top quarks in heavy ion collisions is a novel tool for investigating nuclear parton distribution functions at high Bjorken-x. Although a quark, the top has a short lifetime, decaying predominantly to a W boson and b quark pair, before hadronization. Leptonic final states from the subsequent W boson decay are thus effectively electroweak probes of the medium they traverse before reaching the detector. The CMS collaboration has reported evidence of top quark pair ($\mathrm{t\bar{t}}$) production using data from lead-lead (PbPb) collisions during Run 2. This talk will present the first measurement of $\mathrm{t\bar{t}}$ production utilizing $1.63~\mathrm{nb}^{-1}$ of PbPb data collected by CMS at 5.36 TeV in 2023 and derived using kinematic variables from leptons and jets.

Speaker: Dr Georgios Krintiras (The University of Kansas (US))

top_quarks_CMS.pdf

16:30 → 18:00 Committee Meetings: Committee Meeting

Thursday 25 June

09:00 → 10:15 Plenaries: Jets

Convener: Helen Caines (Yale University (US))

09:00 Experimental Overview of Jets in QCD matter

Speakers: Virginia Bailey, Virginia Bailey (Georgia State University)

VBailey_HPJetOverview.pdf

09:25 Jet interactions and medium response

Speaker: Zhong Yang (Vanderbilt University)

HP26_ZY.pdf

09:50 Experimental review of jet substructure and energy-energy correlators

Speaker: Laura Brittany Havener (Yale University (US))

HP2026_JSEEC_Havener.pdf

10:15 → 10:45 Coffee break

10:45 → 12:00 Plenaries: Jets and smaller systems

Convener: Barbara Jacak (University of California Berkeley (US))

10:45 What can we learn from energy-energy correlators and jet substructure?

Speaker: Joao Lourenco Henriques Barata

HP26_vfinal.pdf

11:10 System-size dependence of jet modifications

Speaker: William Horowitz (University of Cape Town)

260625(HP)Horowitz.pdf

260625(HP)Horowitz.pptx

11:35 Experimental overview of hard probes in small systems

Speaker: Cristian Baldenegro (Massachusetts Inst. of Technology (US))

HardProbesCBaldenegro_v11.pdf

12:00 → 14:00 Lunch break

14:00 → 15:40 Plenaries: Initial state, lQCD, pQCD and ML

Conveners: Berndt Mueller, Berndt Mueller (Duke University)

14:00 Initial state and early-time dynamics

Speaker: ∫ Dana Avramescu (University of Jyväskylä)

hp26_avramescu.pdf

14:25 Lattice QCD and non-perturbative approaches

Speaker: Jorge Luis Dasilva Golan (Brookhaven National Laboratory)

HP_26.pdf

14:50 Perturbative QCD foundations for hard probes

Speaker: Melissa Corona van Beekveld (Nikhef National institute for subatomic physics (NL))

HP2026_pQCD_developments_MvB.pdf

15:15 Machine learning and data science for hard probes

Speaker: Yeonju Go (Brookhaven National Laboratory (US))

20260625_HP2026_AIML_YeonjuGo.pdf

15:40 → 16:10 Coffee break

16:10 → 17:00 Plenaries: Electroweak

Convener: Harald Appelshaeuser (Goethe University Frankfurt (DE))

16:10 Electroweak probes: experiment

Speaker: Gianluca Usai (Universita e INFN, Cagliari (IT))

HP2026-Usai.pdf

16:35 Electroweak probes: theory

Speaker: Xiang-Yu Wu (McGill University)

HP2026_final_xyw.pdf

18:00 → 20:30 Conference Dinner

HP 2026 msueum banquet flyer.pdf

Friday 26 June

08:25 → 10:20 Plenaries: Future and highlights

Convener: Marco Van Leeuwen (Nikhef National institute for subatomic physics (NL))

08:25 Flash talks Announcement

08:30 Flash Talk 1 - Heavy Quark dynamics in QGP using effective field theory

Speakers: Jyotirmoy Roy, Jyotirmoy Roy

HP2026pdf.pdf

08:35 Flash Talk 2 - Bottomonium transport in a strongly coupled quark-gluon plasma

Speakers: Biaogang Wu (Cyclotron Institute, Texas A&M University), Biaogang Wu (Texas A&M University)

flash_talk_v2.pdf

08:40 Flash Talk 3 - Dijet momentum imbalance and azimuthal correlations in Au+Au collisions at sqrts 200 GeV with the sPHENIX detector

Speaker: Tanner Mengel (University of Colorado, Boulder)

tmengel_flash_hp26.pdf

08:45 Flash Talk 4 - Studying of Fragmentation Function and Jet Shapes at RHIC using JETSCAPE

Speaker: Mckenna Renee Sleeth (Vanderbilt University)

HP_Flash_Talk_Sleeth.pdf

08:50 Flash Talk 5 - Probing the Dead Cone Effect with D0-tagged Jet Energy Correlators in STAR

Speaker: Ryan James Hamilton (Yale University (US))

Hamilton_HP2026_FlashTalk_v4.pdf

08:55 Flash Talk 6 - Differential probes of jet evolution with charged energy-energy correlators at ALICE

Speakers: Tucker Hwang (University of California Berkeley (US)), Tucker Hwang

ceec_ft.pdf

09:00 Flash Talk 7 - Covariant Jet Momentum Broadening in QCD Effective Kinetic Theory

Speaker: Ms Isabella Danhoni

flash_talk_isabella.pdf

09:10 Future facilities: the Electron-Ion Collider

Speaker: Dr Xuan Li (Los Alamos National Laboratory)

HP2026_EIC_highlight_XuanLi_v4.pdf

09:35 Future opportunities with heavy ions

Speakers: Enrico Scomparin (INFN Torino (IT)), Enrico Scomparin (Universita e INFN (IT))

Enrico_HP26_v3.pdf

10:00 Conference highlights: initial state and early-time dynamics

Speaker: Benjamin Jacob Gilbert (Lawrence Livermore Nat. Laboratory (US))

HP26_InitialStages_Highlights_Gilbert_Final.pdf

10:20 → 10:55 Coffee break

10:55 → 12:30 Plenaries: Conference highlights

Convener: Jean-Francois Paquet (Vanderbilt University)

10:55 Conference highlights: jets

Speaker: Adam Takacs (CERN TH)

AdamTakacs_HP2026.pdf

AdamTakacs_HP2026.pdf

AdamTakacs_HP2026.pptx

11:25 Conference highlights: electroweak probes

Speakers: Dr Akihiko Monnai (Osaka Institute of Technology), Akihiko Monnai (The University of Tokyo)

hp26_monnai_v1.pdf

11:45 Conference highlights: heavy flavors

Speaker: Stefano Politano (CERN)

hf_summary_hp26_spolitan.pdf

12:05 Next HP and Conference Close-out

Speakers: Enrico Scomparin (INFN Torino (IT)), Roberta Arnaldi (Universita e INFN Torino (IT))

HP28_presentation_PlenaryHP26.pdf