HP2026 Satellite Workshop on Jets and Heavy Flavor Physics

27 Jun 2026, 08:45 → 28 Jun 2026, 20:30 US/Eastern

Georgia State University

The workshop will discuss interpretations of the latest jet and heavy-flavor results presented at the Hard Probes 2026 conference and strategies for future experimental measurements and theoretical directions using jet and heavy flavor probes to deepen our understanding of QCD phenomena. 

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Saturday 27 June

10:00 → 10:10 Introduction: Welcome

10:00 Welcome

Speaker: Megan Connors (Georgia State University)

10:05 Workshop introduction

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

10:10 → 10:40 Morning 1

10:10 Measurements of azimuthal anisotropy of jets in heavy ion collisions

Jets produced in collisions of heavy nuclei lose energy as they pass through the hot, dense nuclear medium known as the quark-gluon plasma produced in the collision. The azimuthal anisotropy of jet production in heavy ion collisions measures the correlations of jets and the initial geometry of the collision, giving insight into path-length dependent energy loss in the medium. This talk will present an overview of experimental results of these observables with a particular emphasis on comparing different experimental techniques used in the measurements. I will also discuss the feasibility and physics impact of performing such measurements at RHIC with the sPHENIX detector.

Speaker: Virginia Bailey (Georgia State University)

10:40 → 11:00 Coffee break

11:00 → 12:20 Morning 2

11:00 Study of jet substructure in p+p collisions with the sPHENIX detector

The sPHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) is designed to study the properties of the Quark-Gluon Plasma (QGP) using high-energy jets as calibrated hard probes. With high-resolution calorimetry and tracking, sPHENIX enables precision measurements of jet substructure observables that are sensitive to medium-induced modifications of parton showers. Jet substructure observables such as the subjet opening angle $\theta_{sj}$ and momentum sharing fraction $z_{sj}$ probe the angular and momentum scales at which the QGP resolves partonic radiation, providing sensitivity to color coherence effects and the medium coherence length, $\lambda_{\perp}$. Systematic measurements across multiple jet radii allow differential access to collinear and wide-angle radiation within jets.

In this work, we present feasibility studies of calorimeter-based measurements of $R_{g}$ in $\sqrt{s}$ = 200 GeV p+p collisions. Jets are reconstructed using the anti-$k_T$ algorithm by 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 via the SoftDrop algorithm. Detector-level distributions are corrected for jet energy scale and resolution effects and unfolded to particle level using multidimensional response matrices constructed from Monte Carlo simulation. Comparisons between unfolded reconstructed MC and generator-level predictions are presented.

Speaker: Jennifer James (Vanderbilt University)

11:30 Fragmentation Function of Charged Pions in Jets using JetScape

The study of jets and jet fragmentation plays a large role in understanding parton evolution within the Quark-Gluon Plasma (QGP). In QCD emissions from jets, photons can fragment from quarks, but these fragmentation photons have not been thoroughly investigated in the context of Heavy-ion Collisions. They could offer insight for investigating jet energy loss mechanisms in the QGP medium. This work utilizes the JETSCAPE framework to select particles inside jets, extracting their momentum fraction z=pTπ/pTjet and angular separation ΔR relative to the jet axis. The main goal is to investigate jet energy loss by analyzing modifications in the fragmentation function and jet shape, specifically for Au+Au collision simulations at 200 GeV (RHIC energies). The analysis first focuses on charged pions, and then extends to photons, within a jet cone radius of 0.4, and restricts all particles to the pseudorapidity range ∣η∣<1.1. Simulation results from the charged pion fragmentation function could provide valuable information on what to look for if there are any signatures of energy loss from fragmentation photons. This study aims to prepare for medium-modified fragmentation function measurements using sPHENIX data from Run2025, offering an opportunity for experimental validation.

Speaker: McKenna Sleeth (Vanderbilt University)

12:00 Discussion

12:20 → 13:30 Lunch

13:30 → 14:00 Afternoon 1

13:30 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.

Speaker: Ritoban Datta (Wayne State University)

14:00 → 14:30 Coffee break

14:30 → 16:30 Afternoon 2

14:30 New Insights into QCD Dynamics in p+Au Collisions from the Multiplicity Dependence of Charmonium Production at \sqrt{s}=200 GeV with PHENIX

We will present new PHENIX measurements of charmonium production in
p+Au collisions at \sqrt{s}=200 GeV and discuss their implications for
QCD dynamics in small collision systems. These results probe the
possible roles of multi-parton interactions, long-range partonic correlations, and novel final-state effects in asymmetric p+Au
collisions at RHIC energies, while carefully accounting for potential
auto-correlation biases identified in previous p+p studies. PHENIX
offers a unique experimental configuration with spectrometers spanning
forward, mid-, and backward rapidities. In particular, the muon arm
spectrometers enable studies of multiplicity dependence in both small-
and large-Bjorken-x regions of p+Au collisions. Using this broad
rapidity coverage, we study the local event-activity dependence of
J/\psi production with a rapidity separation between the charmonium
signal and the event-activity estimator. This approach suppresses
auto-correlation effects and provides a cleaner handle on the
interplay between hard and soft QCD processes in p+Au collisions. The
observed trends offer new insight into the mechanisms governing
charmonium production and event activity in cold/hot nuclear matter at RHIC.

Speaker: Dr Ming Liu (Los Alamos)

15:00 Partonic effects on the charm azimuthal correlations in relativistic p + p collisions

Measurements of heavy flavor quark correlations in heavy-ion collisions are crucial to understand the flavor dependence of quark energy loss mechanisms in hot and dense QCD matter. In addition to the heavy-ion collisions, experimental measurements of heavy flavor correlations in $p+p$ collisions can provide insights into the contributions of perturbative and non-perturbative QCD processes to the correlation functions and further help in interpreting correlation measurements in heavy-ion collisions. In this study, we investigate charm quark and $D$-meson correlations using PYTHIA Event Generator and a multiphase transport model (AMPT). By introducing a transport model approach with partonic rescatterings connecting to the initial conditions provided by PYTHIA event generator, effects of the partonic collisions on the charm azimuthal correlations in relativistic $p+p$ collisions are investigated. It is found that the partonic collisions during the lifetime of the partons enhance the away-side correlation and suppress the near-side correlation, whereas hadronization and final state hadronic interactions bring tiny effect to the azimuthal correlations. These findings indicate that partonic effect plays an important role in the azimuthal correlations of heavy flavor particles in relativistic $p+p$ collisions. Our study offers insights into the future experimental measurements of heavy quark correlation at RHIC and LHC energies.

Speaker: Xiaozhou Yu (Fudan University)

15:30 Discussion

18:00 → 20:30 Workshop dinner

Sunday 28 June

09:00 → 10:30 Morning 1

09:00 Study of Energy-energy correlators in heavy-ion collisions

The energy-energy correlator (EEC) inside jets is a sensitive observable for studying jet modification in the quark-gluon plasma (QGP). we employ an updated CoLBT-hydro framework in which a medium scale QM = 2.0 GeV is introduced to separate the vacuum and in-medium stages of the parton shower, enabling a more self-consistent treatment of jet evolution. Using a theoretical background subtraction within the model, the resulting simulation reproduces the recent CMS measurement of the in-jet EEC, and through a decomposition of different contributions, highlights the impact of medium modification on the observable. To further validate the experimental procedure, we also implement the CMS mixed-event background-subtraction method directly in the simulation and find the results are consistent with that obtained with the theoretical background subtraction. Finally, we discuss the effect of jet-flow coupling on EEC.

Speaker: Zhong Yang (affiliate@vanderbilt.edu;member@vanderbilt.edu;employee@vanderbilt.edu;staff@vanderbilt.edu)

09:30 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 copious studies in recent years, namely in the exploration of the Quark-Gluon Plasma (QGP). EECs have been originally proposed to display a clear-cut 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 Madureira (LIP/IST)

10:00 Generalized background subtraction of N-point energy correlator in Heavy Ion Collisions

Energy-Energy Correlators (EEC) probe the dynamics of the quark gluon plasma (QGP) by mapping the final-state energy by mapping the angular distribution of final-state energy. At the Relativistic Heavy Ion Collider (RHIC), $\sqrt{s_{NN}} = 200$ GeV collisions provide a complementary kinematic regime to the LHC, but jet substructure measurements are challenged by lower jet energies and a large soft background. The Whole Event Energy Correlator (wEEC) extends EEC measurements to the full dijet system, capturing both small- and large-angle correlations.
In this talk, we present a Monte Carlo feasibility study of the wEEC and single jet EEC measurement at RHIC energies focusing on background subtraction methodology. We use PYTHIA embedded in a hydrodynamic background to model the heavy-ion environment. By incorporating jet quenching, we study how medium-induced modifications affect the performance of background subtraction and the reconstruction of correlators. These studies explore subtraction and reconstruction methods providing a foundation for future wEEC measurements at RHIC.

Speaker: Laurynette Griffin

10:30 → 11:00 Coffee break

11:00 → 12:20 Morning 2

11:00 Study of Correlation Functions in Archival LEP Data

Correlation functions of the asymptotic energy and charge flux connect the macroscopic structure of collider events to the underlying microscopic dynamics of the Standard Model. This talk presents measurements of the track energy-energy correlator and the one-point charge correlator in DELPHI Open Data in e+e- collisions. The measured energy-energy correlator is 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 measured one-point charge correlator exhibits a clear modulation, in agreement with both the PYTHIA 8.3 Monte Carlo prediction and theory calculation at N3LO in QCD, representing the first direct observation of the differential asymmetry shape in data. This talk also presents phenomenological studies of the correlation functions, motivating future precision physics programs, whether at the FCC-ee or through further analysis of archival LEP data.

Speaker: Jingyu Zhang (Vanderbilt University)

11:30 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 at $\sqrt{s}=91.2\,\mathrm{GeV}$ in $e^+e^-$ collisions, providing a precision vacuum reference and a controlled bridge to possible QGP-like collectivity in heavy-ion collisions. Using archived 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, with the E-scheme axis, defined by the vector sum of the four-momenta of in-jet constituents, to quantify the sensitivity of the measured harmonics to soft jet constituents and recoil effects. The results are compared to multiple modern event generators to test the modeling of vacuum jet substructure.

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 in $V_n$. We further discuss related in-jet azimuthal structures observed in PbPb collisions and examine how the $e^+e^-$ vacuum baseline can help separate vacuum fragmentation, medium response, and possible flow-driven contributions. Future prospects and possible extensions of this study will also be discussed.

Speaker: Kuan Lu (Vanderbilt University)

12:00 Discussion

12:20 → 13:30 Lunch

13:30 → 14:30 Afternoon 1

13:30 Oxygen–Oxygen Collisions: A New Window on the System-Size Evolution of QCD Matter at RHIC and the LHC

Oxygen–Oxygen collisions have recently opened a new avenue for studying the system-size dependence of QCD matter in relativistic nuclear collisions. Positioned between small systems such as pp and pA and large heavy-ion systems such as AuAu and PbPb, OO collisions provide a unique opportunity to investigate how collective phenomena and medium effects evolve with the size and density of the produced system. Recent measurements from RHIC and the LHC indicate that OO collisions exhibit many features previously associated with heavy-ion collisions, including collective flow, multiparticle correlations, and characteristic patterns of identified-particle production, while offering new constraints on the onset of medium-induced effects. This talk presents a brief overview of recent OO results from RHIC and LHC, covering particle production, soft QCD dynamics of small system (azimuthal anisotropy, multiparticle correlations), heavy-flavor and quarkonium observables, strangeness and baryon-to-meson production, and hard probes sensitive to parton energy loss. The status of ongoing analyses and future measurements will also be discussed, emphasizing the emerging role of OO collisions in understanding the limits and properties of strongly interacting QCD matter.

Speaker: Uttam Acharya (Vanderbilt University)

14:00 Jet Charge with Global Event Shapes at the EIC

We combine the tools of global event shapes and jet electric charge into a unified factorization framework to probe quark flavor dynamics in the nucleon and the hadronization process. As a concrete example, we study jet charge measurements with the 1-Jettiness global event shape for Deep Inelastic Scattering (DIS) as a quark flavor probe of unpolarized or polarized parton distribution functions (PDFs) and final state hadronization. We present simulation studies to demonstrate the sensitivity of the 1-Jettiness jet charge observable to quark flavor dynamics. This observable is well-suited for existing HERA data and the future Electron-Ion Collider (EIC).

Speaker: Sonny Mantry (University of North Georgia)

14:30 → 15:00 Coffee break

15:00 → 16:30 Afternoon 2

15:00 Target Fragmentation and Fracture Function Observables at the Electron-Ion Collider

Target fragmentation provides a unique window into the correlation between the struck parton and the remnant system in semi-inclusive deep-inelastic scattering. While current and past studies of nucleon structure have largely focused on current fragmentation observables, the Electron-Ion Collider will enable precision measurements in the target-fragmentation region through its high luminosity, wide kinematic reach, and dedicated forward detection capabilities. These measurements can access fracture functions, which describe the probability of finding the parton in the target while observing a specific hadron produced directly from the target remnant.
In this talk, we discuss key fracture-function observables at the EIC, including leading baryon production, identified hadrons at large rapidity, transverse-momentum correlations, and flavor- and spin-dependent target-fragmentation channels.

Speaker: Wenliang Li (Stony Brook University CFNS)

15:30 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)

16:00 Discussion

16:30 → 17:00 Conclusion