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Welcome

• Zebo Tang (University of Science and Technology of China (CN))

Overview: Initial Stages and Pre-equilibrium of Heavy Ion Collisions

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

Measuring the spatio-temporal characteristics of meduim produced in heavy-ion collisions

• Egor Nedorezov (JINR)

Recently, a large amount of experimental data has been collected in high-energy physics to study the properties of nuclear matter. One of the main interests is to investigate the phase diagram and localize phase transitions from hadronic to quark-gluonic matter. Different techniques are employed to study the hot matter. One of these is femtoscopy, which uses two-particle correlations to extract spatio-temporal characteristics of the emission source. Another approach involves obtaining thermodynamic parameters from the momentum distributions of produced particles using various theoretical models. In this research, we refine our previous method for determining the spatio-temporal characteristics of the fireball by calculating its geometrical dimensions and lifetime using femtoscopy. Specifically, the system volume is calculated in a cylindrical coordinate system, taking into account the radial and longitudinal expansion of the medium within the framework of the Blast-Wave model. A comparative analysis is performed between femtoscopic volumes and those obtained using the Tsallis statistical fit to estimate the system size at kinetic freeze-out and its dependence on collision centrality and energy.

Probing initial geometry through collectivity in d+Au and O+O collisions at STAR

• Zaining Wang (Fudan University)

Probing initial geometry through collectivity in d+Au and O+O collisions at STAR Zaining Wang (for STAR Collaboration) A small system geometry scan provides critical insights into the initial conditions of quark-gluon plasma. The initial state conditions, influenced by structural effects such as the many-body properties of light nuclear shapes, also leave a distinct footprint in the correlations among final-state particles. In this talk, we present preliminary measurements of flow harmonics ($v_2$ and $v_3$) obtained from multi-particle correlations in d$+^{197}$Au, $^{3}$He+$^{197}$Au, and $^{16}$O+$^{16}$O collisions at 200 GeV, based on newly collected data from STAR. These measurements are compared to hydrodynamics with the state-of-the-art $ab$ $initio$ calculations, illustrating the features of initial geometry, sub-nucleon fluctuations, and nucleonic clustering features. This finding highlights a deeper understanding of initial conditions and collectivity in small system collisions.

Study of the 3D Geometry of the Glasma Using 3+1D Glasma Simulations

• Hidefumi Matsuda

In the early stages of heavy-ion collisions, the produced matter forms a high-density gluon system known as the glasma, which is simulated using classical fields based on the Color Glass Condensate (CGC) framework. Recently, significant progress has been reported by many groups in advancing glasma simulations, extending them to three-dimensional models that incorporate the longitudinal structure of the glasma, which had not been considered previously. In this study, we employ the 3+1D glasma simulation method that we recently developed to analyze the three-dimensional geometry of the glasma in Au-Au collisions at $\sqrt{s_{\rm NN}}=200$ GeV. The geometry is found to be sensitive to the impact parameter, and as a result, the intriguing impact-parameter dependence of various observables is observed. We show the 3D geometry of the glasma and an analysis of geometry-dependent observables such as eccentricity, angular momentum, and vorticity. An increase is observed in these observables with larger impact parameters. Interestingly, while angular momentum also grows with impact parameter, its production at mid-rapidity is significantly suppressed for all impact parameter values. We discuss this suppression by comparing it with experimental findings of global polarization (in press in Physical Review D).

Neural network study of the impact of nuclear structures in heavy ion collisions

• Abhisek Saha (Peking University)

Understanding the nuclear structure in heavy-ion collisions is essential, as it critically influences final state observables. However, characterizing the structure of heavy nuclei in high-energy collisions remains challenging. Current simulation methods for modeling final state events based on initial state data are highly reliant on model parameters, requiring extensive tuning and adjustment. To simplify nuclear structure estimation and minimize model parameter dependencies, we propose a novel approach that maps final state observables directly with initial nuclear structure characteristics. Specifically, we develop a regression model using a state-of-the-art neural network architecture, featuring several convolutional layers followed by batch normalization, max pooling, and fully connected dense layers. We train this model with $^{238}U+^{238}U$ ($\sqrt{s_{NN}}=193$ GeV) and $^{129}Xe+^{129}Xe$ ($\sqrt{s_{NN}}=5.44$ TeV) collision data to ensure model robustness across system sizes and collision energies. This allows us to extract quantitative information on nuclear deformation from event-by-event correlations of final state observables, effectively minimizing parameter influence. Our study leverages various three-particle and four-particle correlations, alongside their combinations, to train the models, analyze error distribution patterns, and identify the most effective observables for accurate and precise nuclear deformation estimation. We found that prediction accuracy strongly depends on the type of nuclear deformation used to train the models, with accuracy ranging from $90\%-100\%$, depending on the specific deformation parameters. The results also reveal that flow-transverse momentum correlation plays the leading role in this regard. The method developed in this study aims to advance our understanding of the initial state in heavy-ion collisions, potentially providing a robust framework for probing nuclear structure with reduced computational constraints.

Q&A

Thermalization and quark production in QCD expanding plasmas

• Sergio Barrera Cabodevila (Instituto Galego de Física de Altas Enerxías - Universidade de Santiago de Compostela)

The Boltzmann Equation in Diffusion Approximation (BEDA) can be used as a tool for exploring the thermalization/hydrodynamization of the quark-gluon plasma. In this talk, we address this issue extending the parametric estimates obtained for small coupling in the so-called bottom-up thermalization by Baier, Mueller, Shiff and Son by introducing quarks and antiquarks in the calculation. Then, we look for confirmation of these estimates with numerical solution of the BEDA. This simulation involves a brand new GPU code capable of solving the BEDA in an arbitrary tridimensional configuration in momentum space. A comparison with the widely used Effective Kinetic Theory will be also shown for different setups. We find an excellent agreement between the two approaches, indicating that the much less numerically expensive BEDA approach is an excellent alternative for more realistic implementations.

Rapidity-dependent QGP equilibration in QCD kinetic theory

• Luyao Fabian Zhou (ITP Heidelberg)

Weakly coupled QCD kinetic theory can well describe the non-equilibrium evolution of the Quark-Gluon Plasma in the early stages of high-energy nuclear collisions. Previous studies in homogeneous and boost invariant systems have shown rapid hydrodynamisation and entropy production during the first 1 fm/c. In this work, we relax the assumption of boost invariance and study the early time dynamics for realistic rapidity profiles of initial quark and gluon distributions. Using state-of-the-art 3D initial-state models, we study thermalisation, hydrodynamisation and chemical equilibration of the QGP as a function of rapidity. In addition, we look at the rapidity evolution of initial state perturbations and charge diffusion.

Q&A

Search for the Strange Dibaryons with Baryon Correlations in Isobar Collisions at STAR

• Kehao Zhang (Central China Normal University)

Dibaryons, exotic states composed of six quarks, have long been a subject of interest in understanding the strong interaction beyond conventional hadrons. Among these, strange dibaryons, which contain strange quarks, offer an important role of studying the hyperon-nucleon ($YN$) and hyperon-hyperon ($YY$) interactions . Of particular interest are the spin-0 $H$ ($S$ = -2) and the spin-2 $N\Omega$ ($S$ = -3) dibaryon state, which are considered promising candidates for the strange dibaryon bound state. In heavy-ion collisions, two-particle femtoscopy is a powerful and unique method for extracting information about the spatio-temporal properties of the source, characterising the final state interactions (FSI), and searching for the possible bound states. In this talk, we will present the measurements of baryon-baryon correlation functions, including $p$-$\Xi^{-}$, $\Lambda$-$\Lambda$ and $p$-$\Omega^{-}$ pairs, in Isobar collisions (Ru+Ru, Zr+Zr) at $\sqrt{s_\mathrm{NN}}$ = 200 GeV. The correlation functions are analyzed within the Lednicky-Lyuboshitz formalism. The extracted scattering length and effective range will be presented. Those measured parameters will be compared with recent Lattice QCD and effective theory model calculations. Most importantly, the physics implications for the formation of strange dibaryon ($S$ = -2 and $S$ = -3) bound state will be discussed.

$\Lambda$-n-n searches in ALICE

• Maria Paula Martins Palhares (Universidade de Sao Paulo (BR))

Hypernuclei are bound states formed between nucleons and hyperons. The measurement of their production in high-energy hadronic collisions provides a powerful probe for investigating the interaction forces that bind strange baryons to ordinary nucleons and for testing nucleosynthesis models. Among the light hypernuclei, the possible existance of the $\Lambda$-n-n remains an open question. After the first claim of observation in 2013, no other experimental evidence has been presented supporting its existence, whereas state-of-the-art model calculations do not expect it to be bound. This contribution presents the search for the $\Lambda$-n-n bound system in Pb-Pb collisions collected by ALICE during LHC Run 3 and discuss its consequences in the overall picture of hypernuclei production at the LHC.

Measurement of f_0(980) resonance with ALICE

• Yunseul Bae (Sungkyunkwan University (KR))

The study of exotic resonances provides insights into the non-perturbative regime of Quantum Chromodynamics (QCD). Short-lived resonances such as \( f_0(980) \), \( f_1(1285) \), and \( f_2(1270) \) have been extensively investigated to explore their internal structures, which remain uncertain with possibilities including tetraquark states or meson-meson molecular states. Among them, the \( f_0(980) \) resonance, with a lifetime of approximately 3--5 fm/\( c \) as reported by ALICE, is particularly sensitive to re-generation and re-scattering processes in the hadronic phase, making it highly suitable for such studies. This contribution reports results by ALICE on the \( f_0(980) \) resonance in pp and p-Pb collisions at LHC energy, reconstructing the resonance was reconstructed via its \( \pi^+ \pi^- \) decay channel. New measurements on \( f_0(980) \) resonance production, focusing on its invariant mass spectra and integrated yields were performed. Comparisons with theoretical models were conducted to further understand its internal structure and, the role of exotic resonances as effective probes of the hadronic phase. The increase in statistics provided by the high luminosity of ALICE Run 3 has enabled more precise measurements of exotic resonances, offering additional insights into their properties. Moreover, the production cross-section of \( f_0(980) \) and its ratio to stable hadron yields were studied to provide complementary insights to the Run 2 results, focusing on the feasibility and performance of the measurement with the current Run 3 data. This analysis provides the latest results on the production of \( f_0(980) \), serving as a valuable reference for understanding the characteristics of the hadronic phase.

Probing the structure of light exotic hadron $f_0(980)$ with elliptic flow in p-Pb collisions at the LHC

• Yili Wang (Peking University)

The study of exotic hadrons has long been a topic of great interest for the understanding of Quantum Chromodynamics (QCD). As one of the light exotic hadrons, the structure and constituent quark content of $f_0(980)$ have been debated for decades, with theories suggesting it could be a tetraquark state ($s\bar sq\bar q$) or a hadronic molecule ($K\bar K$). Recently, the CMS experiment has measured the elliptic flow anisotropy $v_2$ of $f_0(980)$ in p-Pb collisions and concluded that $f_0(980)$ is an ordinary $s\bar s$ meson, based on the number-of-constituent-quarks (NCQ) scaling of elliptic flow [1]. Assuming that loosely bound light exotic hadrons can only survive at the kinetic freeze-out of the expanding hadronic matter, we have implemented the first $K\bar K$ coalescence model to a hybrid viscous hydrodynamic and hadronic transport model to calculate the $p_T$-spectra and elliptic flow of $f_0(980)$ in p-Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV. Using the well tuned phase-space distributions of kaons in this collision, our coalescence model results agree well with the CMS flow measurements, providing thus a strong evidence for the $K\bar K$ molecular nature of $f_0(980)$. Our study also indicates that the CMS Collaboration may have unjustifiably ruled out the $K\bar K$ molecular state of $f_0(980)$ by not considering the different $v_2$ scalings in the coalescence of hadrons and the coalescence of quarks[2]. **References** [1] A. Hayrapetyan *et al*. (CMS), arXiv:2312.17092, 2023. [2] Y. Wang, W. Zhao, C. M. Ko, F. Guo, J. Xie, H. Song, in preparation.

Q&A

QCD equation of state in strong magnetic fields at nonzero density

• Arpith Kumar (Central China Normal University)

QCD equation of state (EoS) characterizes the equilibrium properties of strongly interacting hot and dense matter. External factors, especially strong magnetic fields reaching magnitudes comparable to the QCD scale, can significantly influence this characterization. Of particular interest is how such strong magnetic fields affect the changes in degrees of freedom and thermodynamic properties near the QCD transition. To this end, we have carried out lattice simulations of $(2+1)$-flavor QCD using highly improved staggered quarks at the physical pion mass on $32^3 \times 8$ and $48^3 \times 12$ lattices. With magnetic field strength ($eB$) ranging up to $45 m_{\pi}^2 \sim 0.8~{\rm GeV}^2$ and temperature ($T$) window focussed around $T_{pc}$, we observe intriguing non-monotonic behaviours in the $T$-$eB$ dependence of pressure and number density, which are absent at vanishing magnetic fields. We will also discuss how the HRG model and the magnetized ideal gas serve as references for low-$T$, weak-$eB$ and high-$T$, strong-$eB$ regimes, respectively. Furthermore, we present results for higher-order thermodynamic observables, energy and entropy density, highlighting the significant impact of magnetic fields.

Thermodynamics of a quark-meson plasma under external magnetic field

• min zhou (Xi'an Jiaotong University)

We investigate the thermodynamics of a quark-meson plasma under external magnetic field in frame of a two-flavor Nambu-Jona-Lasinio (NJL) model. We calculate the thermodynamic functions and the chiral restoration phase transition to order 1 /Nc in an expansion in the inverse number of colours, which is seen to include mesonic exchange. We discuss the magnetic field effect on the bound and resonant states meson and the associated scattering phase shifts. After that we compute their contribution to the behavior of the bulk thermodynamic quantities, such as thermodynamic potential, entropy and energy densities. Finally, we study the chiral restoration phase transitions beyond mean field level, which shows the inverse magnetic catalysis effect.

Probing Isospin Violation Under Strong Magnetic Fields via the Production of $K^{*0,\pm}$ Mesons in Heavy-Ion Collisions at RHIC

• Subhash Singha (Institute of Modern Physics CAS)

Neutral and charged vector mesons can be sensitive to isospin-violating effects induced by Landau level splitting in the presence of a strong magnetic field ($B$) within a QCD medium~\cite{meson_spiltting_njl}. One such example is the neutral $K^{*0}$ ($d\bar{s}$) and the charged $K^{*+}$ ($u\bar{s}$), which have similar masses and isospin. However, the magnetic moments of their constituent quarks differ significantly, by approximately a factor of five. The recent observation of isospin violation in neutral and charged kaons by NA61/SHINE challenges the assumption of isospin symmetry in QCD, though the cause remains unknown~\cite{na61_isospin}. A difference in $K^{*0,\pm}$ yields due to B-field can feeddown ($K^{*0} \rightarrow K^{\pm} + \pi^{\mp}$,$K^{*\pm} \rightarrow K_{S}^{0} +\pi^{\pm}$) into the inclusive neutral and charged kaon yields, and contribute to the above apparent isospin violation. In this talk, we will discuss the invariant mass peak position and its width, transverse momentum ($p_{T}$) spectra, yields ($dN/dy$), and $\langle p_{T} \rangle$ of $K^{*0,\pm}$ mesons near mid-rapidity, utilizing collisions involving isospin-asymmetric nuclei (Au+Au, Ru+Ru, Zr+Zr) and isospin-symmetric nuclei (O+O), as well as p+p collisions at $\sqrt{s_{NN}} = 200$ GeV. We report on particle ratios, including $K^{*\pm}/K^{*0}$ and $K^{\pm}/K_{S}^{0}$, as a function of $p_{T}$ and centrality in various heavy-ion collision systems. Results from p+p collisions, which are expected to have no B-field effect, serve as a good baseline. Additionally, results from BES-II Au+Au collisions ($\sqrt{s_{NN}} = 7.7 - 19.6$ GeV) will be presented to study the energy dependence of the above ratios. This study will provide comprehensive understanding of Landau levels, isospin violation, and late-stage B-fields in QCD medium.

Q&A

Overview: Collectivity/Polarisation

• Takafumi Niida (University of Tsukuba)

Measurements of Hyperons Global Polarization in Au+Au collisions at BES-II energies from RHIC-STAR

• Tong Fu (Shandong University)
• Xingrui Gou

The observation of hyperon global polarization along the system's angular momentum has revealed the existence of large vorticities in the medium created by heavy-ion collisions. Using the high-statistics data collected by the STAR experiment during the RHIC Beam Energy Scan II (BES-II) program with upgraded detector systems, we present the global polarization measurements for $\Lambda$, $\bar\Lambda$, $\Xi^{\pm}$ and $\Omega^{\pm}$ hyperons in Au+Au collisions at BES-II energies ($\sqrt{s_{\mathrm{NN}}} = 7.7, 9.2, 11.5, 14.6, 17.3, 19.6, 27$ GeV). Specifically, we focus on the possible differences in polarization between $\Lambda$ and $\bar\Lambda$, as well as the polarization behaviors observed in different hyperons ($\Xi^{\pm}$ and $\Omega^{\pm}$). These results provide new insights into the polarization mechanism and vorticity fields in heavy-ion collisions as well as additional constraints on the properties and dynamics of the hot and dense matter created in these collisions.

Measurements of $\Lambda$($\bar{\Lambda}$) hyperons' local spin polarization in Au+Au collisions from the RHIC Beam Energy Scan-II

• Qiang Hu

The second harmonic cosine and sine modulations of the local spin polarization of $\Lambda$ and $\bar{\Lambda}$ hyperons, along the out-of-plane direction ($\langle P_y \rangle$) and along the in-plane direction ($\langle P_z \rangle$), respectively denoted as $\langle P_{2y} \rangle$ and $\langle P_{2z} \rangle$, are newly proposed observables for probing the spin Hall effect (SHE) driven by the gradient of baryon chemical potential. $\langle P_{2y} \rangle$ and $\langle P_{2z} \rangle$ are measured in Au+Au collisions at $\sqrt{s_{NN}} = $ 7.7, 9.2, 11.5, 14.6, 17.3, 19.6 and 27 GeV from the RHIC Beam Energy Scan-II. A monotonic decrease of $\langle P_{2y} \rangle$ for $\Lambda$ with increasing collision energy, and smaller positive $\langle P_{2z} \rangle$ with hints of sign change at $\sqrt{s_{NN}} = 7.7$ GeV are observed. However, $\langle P_{2y} \rangle$ and $\langle P_{2z} \rangle$ for $\bar{\Lambda}$ show no significant energy dependence within the large statistical uncertainties. The local polarization components are influenced by thermal vorticity, shear-induced effects, and baryon chemical potential. The local components and their difference will be presented. These measurements provide valuable insights into the spin dynamics of QCD matter in high baryon density environments.

Observation of $\Lambda$ hyperon local polarization in pPb collisions at $\sqrt{s_{NN}}= 8.16$ TeV

• Chenyan Li (Shandong University (CN))

The observation of hyperon polarization along beam direction ($P_z$) in nucleus-nucleus collisions has opened a new way to study the complex vortical structures of the QGP. With the high-statistics data collected by the CMS experiment, we present the first $P_z$ results for $\Lambda$ and $\bar{\Lambda}$ particles in pPb collision at $\sqrt{s_{NN}}= 8.16$ TeV over a wide transverse momentum ($p_{T}$) and charged particle multiplicity ($N_\mathrm{trk}^\mathrm{offline}$) range. The $P_z$ values decrease as a function of $N_\mathrm{trk}^\mathrm{offline}$, but increase with $p_{T}$. A hydrodynamic model that describes the observed $P_z$ values in nucleus-nucleus collisions by introducing vorticity effects does not reproduce either the sign or the magnitude of the pPb results. These observations pose a challenge to the current theoretical implementation of spin polarization in heavy ion collisions and offer new insights into the origin of spin polarization in hadronic collisions at LHC energies.

Spin polarization of Λ hyperons in small systems using hydrodynamic approaches

• Cong Yi

Recently, CMS collaboration has measured the spin polarization of $\Lambda$ hyperons along the beam direction in p+Pb collision at $\sqrt{s_{NN}}=8.16$. The second Fourier sine coefficient of the spin polarization of $\Lambda$ hyperons along the beam direction decreases as multiplicity increases. This contrasts with the trend of v2 in the p+Pb collision. This finding challenges the picture that spin polarization along the beam direction is induced by anisotropic flow. We have implemented the 3+1 dimensional CLVisc hydrodynamics model with TRENTo-3D initial conditions to investigate the spin polarization of $\Lambda$ hyperons along the beam direction in p+Pb collisions. We have computed the second Fourier sine coefficients of spin polarization along the beam direction as functions of multiplicity, transverse momentum and pseudo-rapidity. We find that the spin polarization induced by thermal vorticity always provides an opposite contribution compared to the shear-induced polarization in p+Pb collisions. The total spin polarization computed by the current hydrodynamic model disagrees with the data measured by LHC-CMS experiments. Our findings imply that other new effects may play a crucial role in p+Pb collisions.

Q&A

Onset of hydrodynamics in a strongly coupled system based on quantum many-body calculation

• Haiyang Shao

Onset of hydrodynamics in the hot medium created in relativistic heavy-ion collisions is a crucial theoretical question. Addressing this problem in a first-principle manner, requires a **real-time**, **non-perturbative** simulation of **a large scale quantum system**, as hydrodynamic behavior emerges only when approaching the continuum limit. The exponentially large Hilbert space of quantum states prevents an exact simulation on classical hardwares. To overcome such a difficulty, we perform such a simulation using the Tensor Network method, which enables simulations of a reduced representation space of large scale quantum many-body systems by keeping only the most essential quantum states contributing to macroscopic quantities. We focus on the massive Schwinger model, a low-dimension analog of quantum chromodynamics (QCD), as it shares the important properties such as confinement and chiral symmetry breaking. Starting from an initial quantum state that mimics hard particle collisions, we *observe the onset of hydrodynamic behavior* that is **consistent with the Bjorken-flow** in all hydrodynamic degrees of freedom: *energy density, fluid velocity, and bulk pressure*. The time scale for the onset of hydrodynamics is found to be consistent with the thermalization time of the quantum distribution function. Both time scales are of the same order as the hydrodynamization time determined by fitting the experimental data, upon a physical matching that extrapolates the 1+1 dimensional Schwinger model to the 3+1 dimension QCD.

Can energy/momentum flow observable reduce the sensitivity to heavy-ion modeling uncertainty?

• Yanru Bao (Huazhong Normal University)

In High-Energy Heavy-Ion Collisions, the anisotropic flow is expected to be directly related to the shear viscosity coefficient. However, it has been known [1] that there is a sizeable modeling uncertainty in the non-equilibrium correction for the Cooper-Frye prescription in multi-stage modeling of heavy-ion collisions, which strongly impacts particle-number-based final-state observables. These discrepancies lead to significant uncertainties in determining the transport properties. In our work, we aim to establish a direct connection between $v_2$ and the shear viscosity coefficient. Our approach is to replace the particle number weight with the transverse energy/moment weight ($E_T^\alpha$ or $p_T^\alpha$, $\alpha>0$) in the cumulant method to calculate the anisotropic flows. Since energy-momentum is locally conserved during hadronization and freeze-out, and transverse energy/momentum flow is less sensitive to the details of hadronization, using energy/moment correlation should reduce the model dependence in intermediate processes. This approach has the possibility to make us recover the early fluid properties better and establish a more direct connection to the anisotropic expansion of the QGP. Additionally, we test the sensitivity of the energy-momentum flow against different non-equilibrium corrections at freeze-out and will discuss the result's dependence on the $\alpha$ weight power. We hope this study can help build better observables to extract the QGP transport coefficient.

Shear and bulk viscosities of gluon plasma across the transition temperature

• Cheng Zhang (Central China Normal University)

Shear and bulk viscosities are two key transport coefficients that characterize the fundamental properties of quark-gluon plasma. They quantify the response of the energy-momentum tensor to the shear flow and divergent flow, serving as crucial input parameters for the phenomenological and transport models that interpret experimental data, e.g. the elliptic flow $v_2$. However, calculating these inherently non-perturbative viscosities within lattice QCD presents challenges due to strong ultraviolet fluctuations in the relevant operators. The traditional approach using the multi-level algorithm has the limitation that it applies only in the quenched approximation, as done in [1, 2]. Recently, the gradient flow method was introduced to address this issue [3], opening the path to studies in full QCD. However, [3] examined only a single temperature, $1.5T_c$, where $T_c$ is the confinement and deconfinement transition temperature. We present results extending [3] to a wide temperature range from $0.76T_c $ to $2.25T_c $, with particular focus on the phase transition region and high-temperature regime. The former helps us to understand how the system behaves when subject to critical change, a topic of wide concern in the community. The latter allows us to compare against the NLO perturbative estimate, which becomes more reliable at high temperature. Our preliminary results suggest that $\zeta/T^3$ peaks around $T_c$, while $\eta/T^3$ increases slowly with temperature without a dip structure around $T_c$. Reference: [1] N. Astrakhantsev, V. Braguta, and A. Kotov, J. High Energy Phys. 04 (2017) 101. [2] N. Astrakhantsev, V. Braguta, and A. Kotov, Phys. Rev. D 98, 054515 (2018). [3] L. Altenkort, A.M. Eller, A. Francis, O. Kaczmarek, L. Mazur, G.D. Moore, and H.-T. Shu, Phys. Rev. D 108, 014503 (2023).

Q&A

Unveiling Critical Behavior in Rapidity Scans Using Cross-Cumulants for intermediate energy collision

• Jianing Li

Recent intermediate-energy heavy-ion collision experiments are intensively examining the QCD phase diagram in search of critical signatures potentially linked to the QCD critical point. Such collisions generate a strongly interacting medium—or “fireball”—that exhibits pronounced inhomogeneities along the rapidity axis, thereby exploring a wide range of the QCD phase diagram simultaneously. This spatial variation creates an exceptional window to investigate critical phenomena in more detail. To leverage this feature, we go beyond the mid-rapidity region and consider higher-order cumulants of conserved charges across multiple rapidity intervals. This “***rapidity scan***” approach provides a novel complement to conventional beam energy scans. To reliably identify critical signals, we must first establish a robust baseline that incorporates non-critical background effects. In this presentation, we detail our progress in constructing such a baseline for rapidity scans. Our analysis shows that baryon number conservation can create cumulant patterns resembling critical behavior, potentially causing misleading interpretations [1]. To address this challenge, we introduce a new class of observables—“cross-cumulants”—specifically tailored for rapidity scans. These observables retain sensitivity to genuine critical fluctuations while reducing the influence of conservation-driven backgrounds. With the aid of hydrodynamic simulations, we illustrate how cross-cumulants can discriminate between authentic critical signals and background-induced artifacts.

Susceptibility functions in hot QCD system

• Mamiya Kawaguchi

Two-point correlation functions of the quark bilinear field, known as meson susceptibility functions, are key physical quantities that provide insights into fluctuations in meson properties and the restoration of chiral and U(1) axial symmetries in the hot QCD system. In this talk, I will present an analysis of these susceptibility functions at finite temperatures. Using effective model approaches, I will demonstrate their temperature dependence and compare the results with lattice QCD observations. Furthermore, the temperature dependence of the topological susceptibility, derived from the meson susceptibility functions, will be discussed. I will then examine the symmetries restoration on the meson susceptibility functions based on the effective model approaches. The effects of rotation on the hot QCD system will also be addressed.

Searching for the QCD Critical Endpoint from Lattice QCD Simulations at a Low Temperature

• Kai-Fan Ye (Central China Normal University)

# Content Significant efforts have been made within the heavy-ion collision community to locate the QCD critical endpoint (CEP). Recent lattice QCD studies using imaginary chemical potentials, based on simulations at temperatures above 120 MeV and utilizing Lee-Yang edge singularities in the complex chemical potential plane, suggest that the critical temperature at the CEP, $T_c^{CEP}$, should be around 110 MeV [[1]](https://arxiv.org/abs/2405.10196). Predictions from effective theories, such as AdS/CFT [[2]](https://journals.aps.org/prd/abstract/10.1103/PhysRevD.110.094006), the Functional Renormalization Group (FRG) [[3]](https://journals.aps.org/prd/abstract/10.1103/PhysRevD.101.054032), and Dyson-Schwinger Equations (DSE) [[4]](https://journals.aps.org/prd/abstract/10.1103/PhysRevD.104.054022), align with this lattice result. In our study, we conduct direct lattice QCD simulations with imaginary chemical potential at a low temperature of 107 MeV, using Highly Improved Staggered Quarks (HISQ) at the physical pion mass on $N_t=10$ lattices. We obtain up to 4th order baryon number fluctuations for each of the 24 values of imaginary baryon chemical potentials ranging from zero to $i\pi$. This enables us to apply multi-point Padé approximants and compute Fourier coefficients of the baryon number density in the complex chemical potential plane. Through these analyses, we examine indications of CEP through the prospective Lee-Yang edge singularities in the complex chemical potential plane at this low temperature. [[1]](https://arxiv.org/abs/2405.10196) David A. Clarke, *et al*., arXiv: 2405.10196 [[2]](https://journals.aps.org/prd/abstract/10.1103/PhysRevD.110.094006) Mauricio Hippert *et al*., Phys.Rev.D 110 (2024) 9, 094006 [[3]](https://journals.aps.org/prd/abstract/10.1103/PhysRevD.101.054032) Wei-jie Fu, Jan M. Pawlowski, and Fabian Rennecke, Phys. Rev. D 101 (2020) 5, 054032 [[4]](https://journals.aps.org/prd/abstract/10.1103/PhysRevD.104.054022) Pascal J. Gunkel and Christian S. Fischer, Phys. Rev. D 104 (2021) 5, 054022 # Category Theory

Fluctuations of conserved charges in strong magnetic fields in (2+1)-flavor QCD

• Jin-Biao Gu (Central China Normal University)

We present the first lattice QCD results of quadratic fluctuations and correlations of conserved charges in (2+1)-flavor lattice QCD in the presence of a background magnetic field. The simulations were performed using the Highly Improved Staggered Quarks with physical pion mass $m_\pi$ = 135 MeV on $N_\tau=8$ and 12 lattices. We find that the correlation between net baryon number and electric charge, denoted as $\chi^{\rm BQ}_{11} $, can serve as a magnetometer of QCD. At pseudocritical temperatures the $\chi^{\rm BQ}_{11}$ starts to increase rapidly with magnetic field strength $eB > 2M^2_{\pi}$ and by a factor 2 at $eB\simeq 8 M^2_{\pi}$. [[1]](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.132.201903) By comparing with the hadron resonance gas model, we find that the $eB$ dependence of $\chi^{\rm BQ}_{11}$ is mainly due to the doubly charged $\Delta$(1232) baryon. Although the doubly charged $\Delta$(1232) could not be detected experimentally, the proxy constructed from its decay products, protons and pions, retain the $eB$ dependence of $\Delta$(1232)’s contribution to $\chi^{\rm BQ}_{11}$. Additionally, under the same kinematic cuts as in the ALICE experiment, the proxy for $\chi^{\rm BQ}_{11}$ still exhibits a strong dependence on the magnetic field. Furthermore, the ratio of electric charge chemical potential to baryon chemical potential, $\mu_{\rm Q}/\mu_{\rm B}$, shows significant dependence on the magnetic field strength and varies with the ratio of electric charge to baryon number in the colliding nuclei in heavy ion collisions. These results provide baselines for effective theory and model studies, and both $\chi^{\rm BQ}_{11}$ and $\mu_{\rm Q}/\mu_{\rm B}$ could be useful probes for the detection of magnetic fields in relativistic heavy ion collision experiments as compared with corresponding results from the hadron resonance gas model. [[1]](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.132.201903) H.-T. Ding, J.-B. Gu, A. Kumar, S.-T. Li, and J.-H. Liu, Phys.Rev.Lett. 132(2024) 20, 201903

Q&A

Anisotropic Flow of Identified Particles in Au+Au Collisions at beam energies between 3.0 and 4.5 GeV from RHIC-STAR

• Xing Wu

In heavy-ion collisions, directed flow ($v_1$) and elliptic flow ($v_2$) represent the first and second harmonic coefficients in the Fourier expansion of the final-state particle azimuthal distribution. These coefficients are sensitive to the equation of state (EoS) and the degrees of freedom in the produced medium. The measurement of $v_1$ and $v_2$ for identified particles provides a powerful tool for investigating the properties of nuclear matter created in heavy-ion collisions. Using data collected by the STAR experiment during the second phase of the Beam Energy Scan (BES-II), we will present a systematic analysis of $v_1$ and $v_2$ for identified particles in Au+Au collisions at beam energies between 3.0 and 4.5 GeV. Number of Constituent Quark Scaling is observed to break down at $\sqrt{s_{NN}} \leq 3.2$ GeV, indicating a hadron-dominated equation of state. However, the scaling is gradually restored as the collision energy increases to 4.5 GeV, signaling the onset of partonic interactions. In addition, negative $v_1$ slopes for kaons are observed in the low $p_T$ region ($p_T < 0.6$ GeV/c). A comparison with JAM model calculations, with and without spectators, suggests that the observed kaon anti-flow at low $p_T$ can be explained by the shadowing effect of spectators in non-central collisions in the high baryon density region.

Measurements of elliptic and triangular flow in forward and backward rapidity in Au+Au collisions at $\sqrt{s_{\rm{NN}}}$ = 19.6 GeV at RHIC-STAR

• Moe Isshiki

Elliptic ($v_2$) and triangular ($v_3$) flow in the forward and backward rapidity regions, are sensitive to the equation of state of hot and dense nuclear matter as well as the initial conditions in heavy-ion collisions. According to hydrodynamic models, the rapidity dependence of $v_2$ and $v_3$ has a strong constraining power on the temperature dependence of specific shear viscosity ($\eta/s$). However, such flow data in the forward/backward regions as well as at lower collisions energies are scarce or even not available for $v_3$. In the second phase of the beam energy scan program (BESII) at RHIC-STAR, data from Au+Au collisions at lower collision energies were taken with the inner TPC ($|\eta|<1.5$) and Event Plane Detector (EPD, $2.1<|\eta|<5.1$) upgrades. At low energy, the EPD covers both participant and spectator regions, allowing us to study the rapidity dependence of azimuthal anisotropy in detail. In this talk, precision measurement of elliptic flow in a wide range of rapidity in Au+Au collisions at $\sqrt{s_\mathrm{{NN}}}$ = 19.6 GeV will be reported and compared to the previous result by the PHOBOS experiment. The first measurement of triangular flow will be also presented over such a wide rapidity range in 19.6 GeV Au+Au collisions. These results will be compared to theoretical models and implications to understanding the temperature and baryon chemical potential dependence of $\eta/s$.

Probing the QCD Phase Structure with Elliptic Flow in Au+Au Collisions at $\sqrt{s_{NN}}$ = 7.7-19.6 GeV at RHIC

• Guoping Wang

Elliptic flow ($v_{2}$) is the second harmonic coefficient in the Fourier expansion of the azimuthal distribution of produced particles, relative to the reaction plane, in heavy-ion collisions. This observable is particularly sensitive to the early-stage dynamics of the system’s evolution and provides insights into the degrees of freedom within the medium. In this talk, we will report $v_{2}$ measurements for a variety of hadrons, including $\pi^{\pm}$, $K^{\pm}$, $p$, $\overline{p}$, $K^{0}_{S}$, $\phi$, $\Lambda$, $\overline{\Lambda}$, $\Xi^{\pm}$ and $\Omega^{\pm}$, based on high-statistics datasets from the second phase of the RHIC Beam Energy Scan (BES-II) program at STAR. The scaling of $v_{2}$ according to the Number of Constituent Quarks (NCQ) for both particles and antiparticles will be examined. Additionally, the NCQ-scaled $v_{2}$ ratios, such as $\pi^{+}$/$K^{+}$, $p$/$K^{+}$, $\pi^{-}$/$K^{-}$, $\overline{p}$/$K^{-}$, $\phi$/$K^{-}$, $\Lambda$/$K^{0}_{S}$ and $\overline{\Lambda}$/$K^{0}_{S}$, across the energy range $\sqrt{s_{NN}}$ = 7.7, 9.2, 11.5, 14.6, 17.3 and 19.6 GeV will be presented. The experimental measurements will be compared with various model calculations, and the resulting insights will be discussed.

Q&A

Overview: Ultra-Peripheral Collision Physics in Heavy Ion Collisions

• Zaochen Ye (South China Normal University)

Azimuthal modulation in light-by-light scattering from ultraperipheral collisions at LHC

• Shuo Lin

Elastic light-by-light (LbL) scattering, one of the most fascinating processes in the Standard Model (SM), has recently been observed in the ultraperipheral collisions (UPCs) of relativistic heavy ions in the Atlas and CMS experiments at the Large Hadron Collider (LHC). Recognizing that the incident quasi-real photons in LbL scattering are strongly linearly polarized, we re-investigate the LbL scattering at UPCs by incorporating the joint dependence of the impact parameter and transverse momenta of the incident photons. We calculate the spectra of transverse momentum, invariant mass and rapidity. Moreover, we show that the linear polarization of incident photons generates a sizable cos2ϕ-type azimuthal modulation, which awaits the test in future LHC and EIC/EicC experiments

Probing New Physics via Photon-Photon Fusion in Pb+Pb Collisions at ATLAS

• Krzysztof Cieśla (AGH University, Kraków)

In ultra-relativistic heavy-ion collisions, large rates of $\gamma\gamma$ processes occur through the interaction of the large electromagnetic fields of the nuclei. These $\gamma\gamma$ interactions enable the study of processes potentially sensitive to physics beyond the Standard Model. In ultra-peripheral collisions (UPCs), characterized by large impact parameter between the nuclei, the outgoing particles exhibit back-to-back production in the transverse plane, which provides precise and efficient identification. This talk presents an overview of recent ATLAS measurements potentially sensitive to physics beyond the Standard Model, including the production of tau leptons, light-by-light scattering, or the production of magnetic monopoles. Measurements of tau lepton production help to constrain its anomalous magnetic moment, a quantity potentially sensitive to physics beyond the Standard Model. Results will be presented on measurements of light-by-light scattering which may be used to set limits on the existence of axion-like-particles (ALPs). Also presented is a search for monopole-pair production in UPCs with monopole masses ranging from 20–150 GeV. The results are compared with a leading-order model of spin-1/2 particle production from photon–photon fusion and a recently developed semi-classical model that includes non-perturbative cross section calculations.

Probing gluon structure with J/ψ photoproduction in isobaric ultra-peripheral collisions at 200 GeV with the STAR

• Zengzhi Li

In ultra-peripheral collisions (UPCs), coherent J/$\psi$ photoproduction has been recognized as one of the most sensitive probes of the nuclear gluon distribution. Recently, STAR published differential measurements on photoproduced J/$\psi$ in ultra-peripheral d+Au and Au+Au collisions at $\sqrt{\mathrm{s_{NN}}}$ = 200 GeV. These results provide important constraints on gluon distribution functions and sub-nucleonic shape fluctuations in both light and heavy nuclei. Compared to d+Au and Au+Au collisions, the collision system size in isobaric collisions ($^{96}_{44}Ru$ + $^{96}_{44}Ru$ and $^{96}_{40}Zr$ + $^{96}_{40}Zr$) lies in between. Therefore, the measurement of coherent J/$\psi$ photoproduction in isobaric UPCs offers a unique opportunity to study the system size dependence of gluon structure. In this talk, we present the differential cross sections of photoproduced coherent J/$\psi$ as a function of rapidity (y) in $^{96}_{44}Ru$ ($^{96}_{40}Zr$) + $^{96}_{44}Ru$ ($^{96}_{40}Zr$) UPCs at $\sqrt{\mathrm{s_{NN}}}$ = 200 GeV. The results will also be shown for different combinations of neutron emission, where neutrons are detected by zero degree calorimeters, which help resolve the photon-gluon emitter ambiguity. More importantly, these data provide crucial constraints on the system size dependence of the gluon structure within nuclei in the kinematic range x$_{parton}$, the momentum fraction carried by the gluon, $\sim 0.015-0.03 $. The results are compared with theoretical model calculations and previous STAR measurements, and the physics implications are discussed.

Coulomb Dissociation Measurement in Isobaric Collisions at $\sqrt{s_{NN}} = 200$ GeV with the STAR Experiment

• Huda Nasrulloh (University of Science and Technology of China)

The STAR experiment collected large-statistics datasets from isobar collisions of $^{96}_{44}\text{Ru}+^{96}_{44}\text{Ru}$ and $^{96}_{40}\text{Zr}+^{96}_{40}\text{Zr}$ ions, offering a valuable opportunity to study Coulomb dissociation via Ultra-peripheral collisions (UPC). Despite having identical mass numbers, these isobars exhibit distinct proton and neutron distributions, leading to variations in their charge and neutron density profiles. These differences are expected to manifest in distinct Coulomb dissociation processes, particularly in the neutron emission spectra measured by the STAR Zero-Degree Calorimeters. In this talk, we present new measurements on neutron emission from $^{96}_{44}\text{Ru}+^{96}_{44}\text{Ru}$ and $^{96}_{40}\text{Zr}+^{96}_{40}\text{Zr}$ collisions at $\sqrt{s_{NN}}=200$ GeV. By analyzing these results, we aim to gain deeper insights into the nuclear structure properties of isobaric nuclei, including their implications for neutron skin. These findings contribute to a better understanding of electromagnetic interactions and their correlation with nuclear studies in heavy-ion collisions.

Q&A

Investigating quantum interference in Drell-Söding process in Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV at STAR

• Xinbai Li (University of Science and Technology of China)

Relativistic heavy-ion collisions offer a unique environment for exploring quantum interference at an unprecedented femtometer scale through photon-nuclear interactions in photoproduction. In exclusive $\pi^{+}\pi^{-}$ production, the resonance and continuum $\pi^{+}\pi^{-}$ components arise from distinct production mechanisms in the $\gamma {\rm A}$ interaction. The continuum $\pi^{+}\pi^{-}$ photoproduction is dominated by Drell-S$\ddot{{\rm o}}$ding process, in which a virtual $\pi^{+}/\pi^{-}$ is diffraction-scattered on the nucleus. The $\sim$5\% difference in the elastic scattering cross sections of $\pi^{-} {\rm A}$ and $\pi^{+} {\rm A}$ around a $\gamma {\rm p}$ center-of-mass energy of approximately 12 GeV in photoproduction in 200 GeV Au+Au collisions at STAR may result in destructive interference. In contrast to $\rho^{0}$ photoproduction, the Entanglement Enabled Spin Interference (EESI) in Drell-S$\ddot{{\rm o}}$ding process may differ due to the absence of the intermediate $\rho^{0}$ and the specific dynamics of the virtual pion-nucleus interaction. In this talk, we will present the first measurement of the diffractive $p_{T}$ spectrum and the spin interference pattern through the amplitude of the second order final state angular cosine oscillation ${\rm A_{2\Delta\phi}}$ measurement for the Drell-S$\ddot{{\rm o}}$ding process in Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV. The results indicate an obvious difference in $p_{T}$ spectrum compared to $\rho^{0}$ photoproduction. We also observe ${\rm A_{2\Delta\phi}}$ with no clear mass dependence for $p_{T} < 0.1$ GeV/c and a notablely stronger interference at the same ${\rm M_{\pi^{+}\pi^{-}}}$ in the Drell-S$\ddot{{\rm o}}$ding process compared to $\rho^{0}$ photoproduction, which provides a unique opportunity to explore the effect of production mechanism on the EESI.

Direct virtual photon measurements in Au+Au collisions with STAR BES-II data

• xianwen bao

In a heavy-ion collision, photons, which do not interact strongly, have the advantage of escaping unimpeded from their emission source. Consequently, photons can carry valuable information about the properties and dynamics of the hot QCD medium created in heavy-ion collisions. Particularly, the transverse momentum distribution of direct virtual photons emitted from the hot QCD medium exhibits sensitivity to the system temperature. The yield of direct virtual photons depend strongly on fireball volume, emission time, total baryon chemical potential, and temperature. The STAR experiment has recorded large datasets of Au+Au collisions in the Beam Energy Scan Phase-II (BES-II) program, spanning center-of-mass energies $\sqrt{s_{\text{NN}}}$ = 3 - 54.4 GeV. In this talk, new results on the direct virtual photon measurements in Au+Au collisions at $\sqrt{s_{\text{NN}}}$ = 14.6 and 19.6 GeV will be presented, including $p_{T}$ spectra and invariant yields. Additionally, prompt photons from initial hard scatterings are estimated using model calculations and the effective temperature is extracted from non-prompt direct photons at $\sqrt{s_{\text{NN}}}$ = 14.6 - 54.4 GeV. The physics implications of direct virtual photon yields and effective temperature will be discussed.

Estimate the magnetic field in heavy-ion collisions by virtual photon polarization and dilepton anisotropy

• Minghua Wei (Anhui University of Science and Technology)

The measurement of the magnetic field created in high-energy heavy-ion collisions is challenging, due to the fact that the magnetic field decays so drastically that in a thermalized quark-gluon plasma the field strength becomes rather weak. By incorporating the weak magnetic effect into the medium, and especially into the production formalism of dileptons from the quark-gluon plasma, the effect of dilepton polarization is studied through the dilepton angular distribution. We find that the anisotropic coefficients in the dilepton spectrum are quite sensitive to the orientation and strength of the weak field. Accordingly, these coefficients provide ideal probes for the magnetic field in realistic experiments. Ref: Phys.Rev.D 110 (2024) 5, 054024

Q&A

Excursion (Zipeng Mountain National Forest Park)

Overview: Jets

• Isaac Mooney (Wayne State University (US))

Measurement of charged jet v2 in Pb-Pb collisions at 5.36 TeV with ALICE

• Yubiao Wang (Central China Normal University CCNU (CN))

A jet is a spray of collimated hadrons originating from the fragmentation of an energetic parton. In heavy-ion collisions, jets traverse the colored medium and lose energy via induced gluon radiation and elastic scattering, which modify jet yields and structure. When the overlap of the colliding nuclei is small, the transverse profile of the quark-gluon plasma (QGP) is expected to become more elliptical in shape. This geometrical shape results in different QGP path lengths for partons emitted at different angles, resulting in an azimuthal anisotropy of the energy loss. This anisotropy alters the $p_{\rm{T}}$ differential yield of jets and is quantified by the second-order flow coefficient, $v_2$, of the jets. Therefore, measurements of jet $v_2$ are expected to be sensitive to QGP properties and to the path length dependence of energy loss. Based on the high statistics data samples collected during Run 3, using ALICE upgraded detectors, we present the first analysis of inclusive charged-particle jet $v_2$ in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.36 TeV. The low $p_{\rm{T}}$ reach of this measurement, which is unique to ALICE, is especially important in constraining theoretical models and elucidating the mechanisms which generate jet $v_2$. The results will be also compared to existing jet $v_2$ measurements.

Search for jet quenching effects in high-multiplicity pp collisions with ALICE

• Artem Kotliarov (Czech Academy of Sciences (CZ))

High-multiplicity (HM) final states of small collision systems exhibit collective phenomena which resemble the well-established signatures of the quark--gluon plasma (QGP) formed in heavy-ion collisions. However, jet quenching has not been observed in small collision systems. Quantification or setting limits on the magnitude of jet quenching in small collision systems is crucial for understanding the limits of the QGP formation. This talk discusses the outcomes of a search for jet quenching effects in HM pp collisions at $\sqrt{s} = 13$ TeV collected by the ALICE detector. The multiplicity of charged particles in a collision is characterized by the signal amplitude from the forward scintillator detector. The analysis measures the semi-inclusive azimuthal acoplanarity distribution of charged-particle jets recoiling from a trigger hadron with high transverse momentum. Provided that the QGP medium is created in HM events, it should deflect produced hard partons relative to their original direction, thus resulting in a broadening of the hadron-jet acoplanarity distribution compared to minimum bias (MB) events. The measured HM acoplanarity distributions exhibit suppression and broadening compared to MB events. These peculiar features are also observed in pp events simulated by the PYTHIA 8, which does not incorporate jet quenching. Further studies of PYTHIA simulations reveal that the observed suppression and broadening originate from a bias induced by the ALICE high-multiplicity trigger. Identifying this bias has implications for all jet quenching searches in small collision systems where selection is made on the event activity.

Imaging the QGP in Ru+Ru and Zr+Zr Collisions using Energy Correlators at STAR

• Andrew Tamis (Yale University)

In proton-proton ($pp$) collisions, 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 particle groups of N constituents in a jet weighted by their energy product, separating perturbative and non-perturbative regimes of jet evolution. In heavy-ion collisions, the quark-gluon plasma has been seen to quench and modify the substructure of jets. Energy correlators can potentially isolate these modifications to identifiable angular scales, including the onset of effects such as color coherence and the medium wake. In this talk, measurements of the two- and three-point energy correlators in $pp$ collisions will be shown alongside the first measurement of N-point energy correlators in isobar collisions (Ru+Ru, Zr+Zr) at RHIC at $\sqrt{s_{\rm NN}}$ = 200 GeV.

Initial stage jet momentum broadening in a light-front Hamiltonian approach

• Carlos Lamas (IGFAE-USC)

We study the momentum broadening of a high energy quark jet in the high-density gluon medium created right after the collision of two ultrarrelativistic heavy nuclei, the Glasma. Previous Glasma studies consider the jet as a classical probe particle, for which position and momentum are simultaneously determined. In this talk, we use the light-front QCD Hamiltonian formalism to treat the jet as a fully quantum state and compute its real-time evolution while propagating through the Glasma classical background fields, that appear as an interaction potential in the quantum evolution of the jet. We present results for the momentum broadening and jet quenching parameter $\hat{q}$ experimented by a jet at approximately mid-rapidity. We then pay special attention to the anisotropies in the momentum broadening between the longitudinal and transverse directions with respect to the collision axis. In opposition to the classical jet analyses, we find that, as the momentum modes of the boost-invariant Glasma are distributed mainly along the transverse direction, the momentum broadening is larger in the transverse than in the longitudinal direction.

Q&A

Semi-inclusive jet mass measurement in Au+Au collisions at √sNN = 200 GeV with STAR

• jeongmyung kang (Sejong University)

In relativistic heavy-ion collisions, a hot and dense QCD medium, known as the Quark-Gluon Plasma, is formed. Simultaneously, hard-scattered partons from these collisions interact with the medium, leading to the production of particle cascades called jets. These jets are modified as they traverse the QGP, a phenomenon referred to as jet quenching. Various jet observables, including jet mass ($M_{\text{jet}}$), have been studied to explore this modification process. For jets with low transverse momenta ($p_{\text{T,jet}}$), distinguishing jets originating from hard scattering remains a significant challenge due to the large contributions from combinatorial background in heavy-ion collisions. To address this issue, methods for measuring recoil jets with respect to high-$p_{\text{T}}$ trigger particles ($9\leq p_{\text{T,trigger}} <30$) in a semi-inclusive manner have been developed. In particular, the STAR Collaboration has employed a mixed-event technique in combination with semi-inclusive recoil jet measurements to provide a data-driven method for correction of uncorrelated background effects. In this study, we extend the method of semi-inclusive recoil jet measurement to the measurement of jet mass ($M_{\text{jet}}$) in central heavy-ion collisions, introducing a two-dimensional measurement methodology as a function of ($p_{\text{T,jet}}, M_{\text{jet}}$) with R = 0.4 as a jet resolution parameter. The validity of this method is evaluated through the Monte Carlo simulations and closure tests, and initial technical results using STAR data will also be presented.

Resonances production in and out of jets in pp collisions at sqrt(s) = 13.6 TeV

• Jimun Lee (Sejong University (KR))

Recent experimental results on two-particle correlations within jets in high multiplicity pp collisions highlight a strong flow-like correlation among constituents. This has brought to the hypothesis of a formation of a hot and dense QCD medium within those jets. This observation suggests new insights of particle interaction dynamics in pp collisions, previously thought to be exclusive to heavy-ion collisions. A key feature of such medium formation is the modified production ratios of different particle species. This is particularly the case for short-lived, strongly decaying resonances, allowing for (pseudo-) elastic collisions with formed hadrons after chemical freeze-out once the medium cools down. In turn, this drastically alters the final-state yields of such particles. To investigate this phenomenon, we analyze the yields of K* and Φ mesons within high-multiplicity jets in pp collisions at √s = 13.6 TeV, using LHC Run 3 data from ALICE. The analysis utilizes charged-particle jets, and per-jet yields of K* and Φ in and out of such jets. The focus on these specific particles is expected to provide valuable insights into the intricate dynamics of QCD medium creation and its influence on particle production mechanisms.

Q&A

Early Thermalization in kenitic theory via spectrum method: The Role of Pair-Correlations

• Shuai Lu (Tsinghua University)

Early Thermalization in kenitic theory via spectrum method: The Role of Pair-Correlations ------------------------------------------------------------------------ Relativistic hydrodynamics has provided an excellent description of the Quark-Gluon Plasma (QGP) produced in heavy-ion collisions. However, as a framework for describing collective behaviors in many-body systems at the mesoscopic scale, hydrodynamics fails to address the **early thermalization** problem of the QGP. In this work, we calculate the **thermalization time** of a relativistic many-body system at the microscopic scale within the framework of **kinetic theory**, focusing on the **nonlinear** evolution of the **pair-correlation** distribution function—an aspect typically neglected—alongside the one-particle distribution function. The spectrum method is employed to reformulate two coupled equations that describe the evolution of both the one-particle distribution function and the pair-correlation function, derived from the Bogoliubov–Born–Green–Kirkwood–Yvon hierarchy. The equations are numerically solved for general initial conditions, and the thermalization time is extracted from the evolution of both bulk viscosity and the shear-stress tensor. In summary, we compare the thermalization times across three models: (1) a pair-correlation model, (2) a nonlinear Boltzmann model, and (3) a linear Boltzmann model, revealing the validity of each scenario within the context of thermalization dynamics.

Light flavor particle production as a function of transverse spherocity in pp collisions at 13 TeV measured by ALICE

• Adrian Fereydon Nassirpour (Sejong University (KR))

High-multiplicity proton-proton (pp) and proton-lead (p-Pb) collisions at the LHC have revealed that even smaller collision systems show the onset of phenomena typical of heavy-ion collisions. Strangeness enhancement and collective flow, two examples of such phenomena, suggest that light-flavor hadron production arises from complex mechanisms of which relative contributions evolve smoothly from low to high multiplicity collisions across different collision systems. Furthermore, observations suggest that the relative contributions of different processes evolve smoothly from low to high multiplicity collisions. This is puzzling in a theoretical context, since it implies that pp collisions cannot be seen as an incoherent sum of parton-parton scatterings, contrary to the modelization in most Monte Carlo event generators, such as PYTHIA. Moreover, these signatures have historically been attributed to the strongly interacting medium formed in heavy-ion collisions, which challenges current theoretical frameworks in the context of smaller collision systems. Studies on multi-differential strange particle production in small systems can be utilized to gain insight into the various final state effects at play and represent an essential baseline for heavy-ion studies. This contribution presents new results from ALICE on light-flavor particle production as a function of the transverse spherocity in pp collisions, measured at \sqrt{s} = 13 TV. Events that are either "isotropic" (dominated by multiple soft processes) or "jet-like" (dominated by one or few hard scatterings) can be selected utilizing narrow selections in multiplicity and spherocity. Predictions from state-of-the-art Monte Carlo generators are compared with the obtained experimental results.

Peculiarities of charged hadron production at PHENIX(RHIC) and MPD(NICA) experiments

• Daria Larionova

One of the important goals of the PHENIX ($\sqrt{s_{NN}}$ = 200 GeV) and upcoming MPD $\sqrt{s_{NN}}$ = 9.2 GeV experiments is to study QCD phase transition and to investigate possible QGP formation in small collision systems (in the case of PHENIX) or at low energies (in the case of MPD). With that purpose PHENIX provided a comprehensive study of identified charged hadron production ($\pi^{\pm}$, $K^{\pm}$, $p$, $\bar{p}$) in $p$+Al, $^3$He+Au, Cu+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV and U+U collisions at $\sqrt{s_{NN}}$ = 193 GeV. Meanwhile, the upcoming MPD experiment is focused on studying charged hadron production in Bi+Bi collisions at $\sqrt{s_{NN}}$ = 9.2 GeV, based on UrQMD simulations. Identified charged hadron invariant transverse momentum ($p_T$) and transverse mass ($m_T$) spectra obtained from both PHENIX and MPD experiments were analyzed using the Blast-Wave model, which allowed to estimate the freeze-out temperatures and radial flow velocities. The nuclear modification factors and particle yield ratios, $K/\pi$ and $p/\pi$, are systematically studied across different centrality classes in both small ($p$+Al, $^3$He+Au) and large (Cu+Au, U+U) collision systems. This analysis provided estimates of the contributions from fragmentation and recombination processes to charged hadron production at the PHENIX energy. To gain a deeper insight, the experimental results are compared with theoretical predictions from the AMPT and PYTHIA8/ANGANTYR models. Additionally, the study of $p/\pi$ ratios measured in Bi+Bi collisions at the MPD experiment enabled the calculation of the chemical freeze-out temperature and the corresponding baryon chemical potential for the MPD energy regime. The results obtained from PHENIX and MPD are compared and summarized in the context of the QCD phase diagram. We acknowledge support from Russian Ministry of Education and Science. State assignment for fundamental research (code FSEG-2025-0009).

Q&A

Strange hadrons reconstruction in Au+Au collisions at 27 GeV energy with the STAR experiment

• Artem Timofeev (Joint Institute for Nuclear Research)

The study of strange hadrons plays a critical role in understanding the properties of hot and dense nuclear matter created in heavy-ion collisions, as they provide unique insights into the quantum chromodynamics phase transition and the possible formation of a quark-gluon plasma. Strangeness enhancement, first proposed as a signature of quark-gluon plasma, arises from the high production rate of strange quarks in deconfined matter compared to hadronic interactions. Strange hadrons, such as Xi and Omega hyperons, are particularly sensitive probes because of their relatively low production in ordinary hadronic collisions and their ability to retain information about the conditions at chemical freeze-out. In this work, the spectra of strange hadrons is studied as a function of transverse momentum for different rapidities and collision centralities, providing information on the dynamics of the hot matter and the chemical freeze-out parameters. Particle signal was extracted via invariant mass technique using different topological cuts. Precise measurements of strange particles yields in Au+Au collisions have potential to deepen our understanding of physics of strangeness and extract the chemical freeze-out parameters of hot matter.

Searching the colliding energy and system size thresholds of QGP production in heavy-ion collisions with Ω/φ ratios

• Yuan Weiguang (清华大学)

$\quad$Heavy-ion collisions provide a unique opportunity to study the properties of the QCD matter at varying temperatures, densities and system volumes. $\Omega$ and $\phi$ hadrons, composed merely of strange quarks, have relatively small hadronic interaction cross sections and can be utilized to study the matter properties at its early stage. In Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV and Pb+Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV, significant $\Omega$ enhancement over $\phi$ have been observed at intermediate transverse momentum in central collisions, which can be explained by their productions through coalescence of strange quarks in Quark-Gluon Plasma (QGP). Hence the energy threshold of QGP production (or onset of deconfinement) in heavy ion collisions can be explored by measuring the colliding energy dependence of $\Omega/\phi$ enhancement. It can also be expected that the measurement of $\Omega/\phi$ ratios in different colliding systems may indicate the minimum colliding system size required to produce QGP. $\quad$ In this talk, we will present new measurements of strange hadron production in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 9.2, 11.5, 14.6, 17.3 and 19.6 GeV using high statistics STAR BES-II data. The transverse momentum ($p_T$) spectra, centrality dependence of yields, nuclear modification factor and the particles ratios ($\phi/K$ ) will be presented. In particular, the energy and centrality dependence of $\Omega$/$\phi$ ratios in BES-II energy range will be presented. Besides, the $\Omega/\phi$ ratios in smaller colliding systems including O+O, d+Au, and isobar collisions at $\sqrt{s_{NN}}$ = 200 GeV will also be shown and compared to the Au+Au data at the same colliding energy. These results will be compared to theoretical calculations and physics implications will be discussed.

Production of light nuclei in Au+Au collisions with the STAR BES-II program

• Liubing Chen (Central China Normal University)

Production of light nuclei in Au+Au collisions with the STAR BES-II program Liubing Chen(for the STAR Collaboration) Central China Normal University The studies of the production of light nuclei, such as deuteron, triton, and helium nuclei in heavy-ion collisions, are essential for understanding the dynamics of nuclear matter under extreme conditions and provide valuable insights into the underlying equation of state. In addition, the yields and ratios of light nuclei serve as an effective method for distinguishing between the thermal and coalescence models.The significantly larger datasets from the STAR Beam Energy Scan phase-II, combined with a wider collision energy range extending to the high baryon density region and enhanced detector capabilities, allow for more precise and comprehensive measurements compared to phase-I. In this talk, we will present measurements of light nuclei production, including p, $\bar{\mathrm{p}}$, d, $\bar{\mathrm{d}}$, t, $^{3}\mathrm{He}$ at $\sqrt{s_{\mathrm{NN}}}$ $\mathrm{\geq}$ 7.7 GeV and p, d, t, ${^3{\mathrm{He}}}$, ${^4{\mathrm{He}}}$ at $\sqrt{s_{\mathrm{NN}}}$ ${<}$ 7.7 GeV, in Au+Au collisions at BES-II energies of $\sqrt{s_{\mathrm{NN}}}$ = 3 - 27 GeV. The results will cover the centrality and rapidity dependence of transverse momentum ($p_{\mathrm{T}}$) spectra and dN/dy. We will also report the coalescence parameters ($B_{\mathrm{A}}$), along with the kinetic freeze-out temperature ($T_{\mathrm{kin}}$) and collective velocity ($\beta_{\mathrm{T}}$) for each nucleus.The physics implications of these results will be discussed.

Q&A

Overview: Heavy Flavor

• Shanshan Cao (Shandong University)

Measurements of charm-strange baryons in pp collisions with ALICE

• Jaeyoon Cho (Inha University (KR))

The measurements of the production of charm quarks at the LHC have provided an essential ingredient for understanding their hadronization mechanism in hadronic collisions. The observation of enhanced charm-baryon production compared to meson production has led to a reconsideration of the assumption on the universality of the fragmentation process across different collisions systems, which resulted in a usage of fragmentation functions benchmarked from $\mathrm{e}^{+}\mathrm{e}^{-}$ collisions in calculations of cross sections for hadronic collisions. The baryon enhancement was found to be more prominent when the charm baryon includes also a strange quark. Theoretical models have attempted to explain these measurements by incorporating new mechanisms that enhance baryon production with resepect to $\mathrm{e}^{+}\mathrm{e}^{-}$ collisions, such as colour reconnection mechanisms beyond leading-colour approximation, coalescence mechanisms for the hadron formation, or feed-down contributions from excited states of charmed hadrons that are currently unobserved. However, the production mechanisms of charm-strange baryons and the origin of this enhancement are still not fully understood, even though the aforementioned theoretical approaches provide a better description of measurements of charm baryon without strangeness. This challenge suggests that charm-strange baryons may offer potential guide for further understanding of the charm hadronization in pp collisions. The ALICE Collaboration has measured charm-strange baryons, $\Xi_{\mathrm{c}}^{0,+}$ and $\Omega_{\mathrm{c}}^{0}$ in pp collisions at midrapidity, shedding light on the role of strangeness in the hadronization process. This contribution presents the measurements of $\Xi_{\mathrm{c}}^{0,+}$ and $\Omega_{\mathrm{c}}^{0}$ baryons in pp collisions at $\sqrt{\it{s}}$ = 13 TeV using data samples collected during Run 2. The charm hadronization mechanism will be discussed by comparing these measurements with theoretical predictions. Furthermore, a first look at new results for charm-strange baryon measurements in pp collisions at $\sqrt{\it{s}}$ = 13.6 TeV collected during Run 3 will be introduced.

\XicZero\ production as a function of multiplicity by \XicZeroToPiXi\ in pp collision at $\sqrt{s}=13$ TeV with ALICE

• Tao Fang (Central China Normal University CCNU (CN))

Measurements of the production of heavy-flavour hadrons in proton–proton (pp) collisions provide an important test of quantum chromodynamics (QCD). The heavy-flavour production cross section can be calculated using the factorisation approach as a convolution of three factors: the parton distribution functions (PDFs), the partonic cross section calculated with perturbative QCD calculations, and the fragmentation functions (FFs). Recent measurements of the baryon-to-meson (${\Lambda^+_{\rm{c}}/\rm{D}^0}$, ${{\Sigma^{0,++}_{\rm{c}}}/\rm{D}^0}$, ${\Xi^{0,+}_{\rm{c}}/\rm{D}^0}$ and ${\Omega^0_c/\rm{D}^0}$) ${p_{\rm{T}}}$-differential yield ratios in pp collisions are inconsistent with measurements in $\rm{e^+e^-}$ collision, indicating that the hadronization of charm quarks is not a universal process among different collision systems. The ${p_{\rm{T}}}$-differential yield ratio of ${\rm{\Lambda^+_c/D^0}}$ shows a significant multiplicity dependence, which implies that the charm hadronization mechanism is sensitive on the color-charge density of the collision. Further studies performed on different charm-hadron species with larger mass and a different quark content, as the measurement of the multiplicity dependence of ${\rm{\Xi^0_c/\rm{D}^0}}$ yield ratio performed by ALICE, presented in this contribution, can provide further constraints on the study of charm hadronization.

Strange Charm-Meson Production in pp Collisions at $\sqrt{s} = 13.6$ TeV with ALICE

• Luca Aglietta (Universita e INFN Torino (IT))

Strange Charm-Meson Production in pp Collisions at $\sqrt{s} = 13.6$ TeV with ALICE Precise measurements of charm-strange hadron production play a critical role in testing perturbative QCD calculations based on the factorization approach. Moreover, comparing the production yields of strange relative to that of non-strange charm hadrons in different colliding systems provides essential insights into heavy-quark hadronization in hadronic collisions and helps constrain models with different approaches to quark hadronization. In this context, several excited charm-strange states have been observed in recent years, but their production yields in hadronic collisions remain unmeasured. Quantifying these yields is essential for understanding charm quark hadronization, as their decays contribute significantly to the yields of ground-state charm hadrons. Furthermore, studying the production of short-lived resonances offers insights into the hadronic phase of the system formed in heavy-ion collisions, which may also manifest in smaller collision systems. This contribution presents the ALICE Collaboration's measurements of production-yield ratios of $\mathrm{D_s}^+$ to $\mathrm{D}^+$ mesons at $\sqrt{s} = 13.6$ TeV as a function of charged particles multiplicity, and compares them to state-of-the-art theoretical predictions. Moreover, it shows the first production measurements of the orbitally excited charm-strange mesons $\mathrm{D_{s1}}(2536)^+$ and $\mathrm{D_{s2}}^{*}(2573)^+$ in proton-proton collisions at $\sqrt{s} = 13$ TeV in two multiplicity classes and at $\sqrt{s} = 13.6$ TeV as a function of transverse momentum. These studies explore the influence of surrounding color-charge density on charm quark hadronization and investigate the potential impact on charm-strange resonance production from a hadronic phase in high-multiplicity proton-proton collisions by analyzing results across different event-multiplicity intervals.

sPHENIX heavy flavor physics prospects at RHIC

• Xudong Yu (Peking University)

sPHENIX is a cutting-edge experiment at the Relativistic Heavy Ion Collider (RHIC), focused on heavy-flavor and jet physics. Its design enables high-precision measurements in 200 GeV p+p and Au+Au collisions. The sPHENIX tracking system includes the Monolithic Active Pixel Sensor-based Vertex Detector (MVTX), Intermediate Silicon Tracker (INTT), Time Projection Chamber (TPC), and TPC outer tracker (TPOT), all operating together in a hybrid of full streaming (MVTX and INTT) and extended triggered readout mode (TPC and TPOT). Additionally, sPHENIX features a large-acceptance calorimeter system, which introduces the first barrel hadronic calorimeter at RHIC. This advanced system facilitates the exploration of Quark-Gluon Plasma (QGP) properties through high-statistics, unbiased data samples, including fully reconstructed heavy-flavor hadrons and jets with exceptional precision. In the 2024 run, sPHENIX has been fully commissioned, collecting 100 billion unbiased p+p collisions. In the 2025 run, sPHNEIX plans to collect high statistics Au+Au collisions. In this talk, we will present the progress toward the first heavy-flavor physics results at sPHENIX, and performance projections for the entire heavy flavor physics program, especially the world leading b-physics program and the first measurement of Lambda_c/D0 in p+p collisions at RHIC.

Q&A

Quantum simulation of SU(2) Yang-Mills theory on a (2+1) dimension small lattice with staggered fermion

• Zhen-Xuan Yang (Fudan University)

In recently years, the real-time evolution based on the Hamiltonian formulation of the lattice gauge theories has been investigated to challenge the so-called sign problem which is the inefficient sampling issue of the quantum Monte Carlo method when we have topological terms, chemical potentials or real time. Thanks to the recent rapidly developed quantum computing technology, it is reasonable to believe the quantum computing can deal with the large Hilbert space when the gauge bosons increasing since the computational resources increase exponentially with the growth in the number of qubits. To demonstrate the feasibility of this scheme, we study the real-time simulation of SU(2) Yang-Mills theory on a (2+1) dimension small lattice with staggered fermion. We perform a digital quantum simulation of the system based on classical emulation. We simulate the entanglement among different points and the entanglement between gauge bosons and staggered fermions to investigate the thermalization of the system. We also calculate the pair production by setting specific initial state. The two entanglement entropies both increase at first and then stabilize around some constants while fluctuating. The pair production also show such a tendency and an obvious dependence on the mass of the fermion mass.

Finite-temperature dynamics of X(3872)

• Víctor López Pardo

We analyze the finite-temperature properties of the X(3872), assuming it to be a tetraquark, with a focus on its formation and survival within the extreme environment of heavy-ion collisions. Using the Born-Oppenheimer approximation and the large-Nc limit, we estimate the potential of this exotic state from zero-temperature lattice QCD results of hybrid potentials. Extending this framework to finite temperatures we explore the conditions necessary for X(3872) formation and its in-medium dissociation. We also implement a dynamic coalescence model, which provides a mechanism for the regeneration of X(3872) inside the quark-gluon plasma. The framework is versatile, with applications to other exotic hadrons, making it a valuable tool for understanding the fate of exotic QCD bound particles in extreme conditions.

In-medium bottomonium properties from lattice NRQCD calculations with extended meson operators

• Wei-Ping Huang (Central China Normal University)

Quarkonium production can be used to probe the matter formed in ultrarelativistic heavy-ion collisions. However, for theoretical understanding of the experimental results on quarkonium production in heavy-ion collisions it is necessary to know if and which quarkonium states exist above the crossover temperature, $T_c$ and what are the in-medium masses and widths of different quarkonium states. In this talk we will focus on the lattice QCD study of in-medium bottomonium properties [1]. In-medium bottomonium properties are encoded in the spectral functions, which are related to the Euclidean time correlators calculable on the lattice. We will present lattice QCD studies of 1S, 2S, 3S, 1P, 2P and 3P bottomonium correlators for $T \simeq 133-250$ MeV [1], where the 3P state is explored for the first time. These calculations are performed with non-relativistic QCD (NRQCD) approach for the bottom quark and on (2+1)-flavor gauge backgrounds using highly improved staggered quark (HISQ) action near physical point. In our study we use correlators of extended bottomonium operators [2, 3] to gain optimized overlaps with specific states and to be more sensitive to thermal effects. Compared to the previous studies that are based on a single lattice spacing per temperature value and temporal extent $N_{\tau}=12$, we use two lattice spacings and lattices with the temporal extent $N_{\tau}=16-30$. We find that all bottomonia states below the open beauty threshold exist above $T_c$, including 3P state. We will show the temperature dependence of the thermal widths and in-medium masses extracted from the bottomonium correlators with physically-motivated ansatzes for the spectral function. We find that, within estimated errors, the bottomonium masses do not change compared to their vacuum values for all temperatures under our consideration, while non-zero widths for different bottomonium states can be observed. These observations suggest excited bottomonium states still exist above $T_c$ and screening is not the likely source of bottomonium dissociation. References: [1] H.-T. Ding, W.-P. Huang, R. Larsen, S. Meinel, S. Mukherjee, P. Petreczky, work in progress. [2] R. Larsen, S. Meinel, S. Mukherjee, P. Petreczky, Phys. Rev. D 100 (2019) 074506. [3] R. Larsen, S. Meinel, S. Mukherjee, P. Petreczky, Phys. Lett. B 800 (2020) 135119.

Q&A

Quarkonium production with ALICE in Run 3

• Yiping Wang (University of Science and Technology of China (CN))

Quarkonia are a valuable tool to investigate strongly interacting medium under extreme conditions, and particularly Quark Gluon Plasma (QGP). In heavy ion collisions, heavy quarks are produced in the early stages of the collisions and thus they experience the whole QGP evolution, allowing to investigate its properties. In addition, at LHC energies, (re)generation process has been found to have an impact on the production of charmonium. In pp collisions, quarkonium production can act as the reference in heavy ion collisions. In parallel, they can be used to test the QCD models, constraining more and more theory calculations. The ALICE collaboration has collected sizeable data samples in pp and Pb-Pb collisions in Run 3, allowing to increase the precision of the existing measurements. In this presentation, preliminary results of ψ(2S)-to-J/ψ ratio in pp 13.6 TeV collisions, as well as the cross section of J/ψ will be presented. Performance findings of bottonium and X(3872) will also be discussed.

Measurements of charm-hadron pairs production in proton--proton collisions with ALICE

• Pengzhong Lu (University of Science and Technology of China (CN))

Multiple Parton Interactions (MPI) play a crucial role in hadron-hadron collisions, contributing to the complexity of the final state in high-energy physics experiments. In these interactions, multiple partons from each hadron can simultaneously interact within a single collision event. Among the various MPI scenarios, Double-Parton Scattering (DPS) is the simplest form, where two distinct parton-parton scatterings occur simultaneously. A key element in describing DPS in proton-proton collisions is the effective cross-section, a phenomenological parameter related to the transverse overlap function between partons within the proton. Studying DPS provides valuable insights into the evolution equations of Quantum Chromodynamics (QCD), particularly regarding multi-parton distributions and potential correlations in color and spin degrees of freedom. The production of heavy quarks, specifically charm and beauty quarks, arises from hard-parton scatterings due to their relatively large masses. As a result, DPS processes involving heavy-quark pairs can be studied by measuring the production cross sections of charm-hadron pairs. In this context, we present recent measurements of D$^0$–D$^0$, D$^0$–J/$\psi$, and J/$\psi$–J/$\psi$ pairs at both midrapidity and forward rapidity in proton-proton (pp) collisions. These measurements are based on Run 2 data at $\sqrt{s}$ = 13 TeV and Run 3 data at 13.6 TeV, collected using the ALICE detector at the Large Hadron Collider (LHC).

Charmonium production in Pb-Pb collisions at forward rapidity with ALICE

• Sara Garetti (Université Paris-Saclay (FR))

Quarkonium production in high-energy lead-lead (Pb-Pb) collisions is a key tool for exploring both the perturbative and non-perturbative aspects of quantum chromodynamics (QCD) calculations. Charmonia are bound states consisting of a charm and an anti-charm quark. Their production process can be divided into two stages: the creation of the heavy quarks and the formation of the bound state. The first stage occurs during initial hard parton-parton scatterings with large momentum transfer, which can be accurately described using perturbative QCD. The second stage, involving long-distance interactions and soft momentum scales, is a non-perturbative process. Studying the production of $\psi$(2S) in Pb-Pb collisions is important for understanding how quarkonium states are modified in the quark-gluon plasma (QGP). The $\psi$(2S) is more loosely bound than the J/$\psi$, and its amount of suppression in the medium can provide insight into the effects of the deconfined medium. The double ratio of $\psi$(2S) to J/$\psi$ in Pb-Pb relative to pp collisions helps to quantify the differential suppression of these two states, offering a clearer picture of the properties of the QGP and its impact on different charmonium states. In this talk 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 \sqrts. The analysis is based on the data collected in 2023 by the upgraded ALICE detector during LHC Run 3, which provides higher statistics compared to previous data-taking periods. The $\psi$(2S)-to-J/$\psi$ double ratio will also be reported. The results will be compared to similar measurements from data collected during LHC Run 2.

Q&A

Recent results of quarkonium production in LHCb

• Youen Kang (Tsinghua University (CN))

Quarkonium production has long served as a probe for heavy quark interaction with nuclear medium. In small collision systems, quarkonia can be modified by initial state effects like shadowing, and final state effect like interacting with co-moving particles. The possible signature due to potentially existing deconfined medium (Quark Gluon Plasma) need to be disentangled from all aforementioned effects, to which measurements from small to large collisions systems of different probes, such as quarkonia, are needed. In this contributions, we will present LHCb results on psi(2S) to J/psi production ratio in pp, pPb (forward and backward) and PbPb collisions, and excited-to-ground-state production ratio of Upsilon mesons in pp collisions, along with comparisons with theoretical models and other measurements.

Measurement of $J/\psi$ energy correlator in $p$+$p$ collisions at $\sqrt{s}=500$ GeV at STAR

• Dandan Shen (shandong university)

The $J/\psi$ meson, consisting of a charm quark and its antiquark, serves as an exceptional testing ground of Quantum Chromodynamics (QCD). However, our understanding of its underlying production mechanism remains incomplete. One of the principal challenges lies in experimentally disentangling perturbative from non-perturbative process contributions. The recently proposed $J/\psi$-energy correlator observable shows a remarkable ability to distinguish between soft and hard processes, thereby establishing the observable as a potent tool for investigating $J/\psi$ production mechanism. Theoretical calculations further indicate that the $J/\psi$-energy correlator, observed within the $J/\psi$ helicity frame, possesses a strong discriminatory power against existing models. In this talk, we will present the first measurement of the $J/\psi$-energy correlator in hadron collisions. The study is conducted by reconstructing the $J/\psi$ via its di-electron decay channel at mid-rapidity ($|y|<1$), within the transverse momentum range of $5<p_T<10$ GeV/$c$, in proton-proton collisions at $\sqrt{s_{_{\rm NN}}}=500$ GeV at RHIC-STAR experiment. By comparing $J/\psi$ energy correlator with different model calculations, we aim to provide a robust basis for distinguishing among the existing $J/\psi$ production models.

Measurements of Quarkonia v2 for Pb-Pb collisions at √sNN = 5.36 TeV using Run3 data of ALICE at the LHC

• Dhananjaya Thakur (Universita e INFN Torino (IT))

Q&A

Adjourn