Studying experimental observables is a key benchmark for validating theoretical models in high energy physics. In this work, we employ the PACIAE 4.0 model to simulate nonsingle diffractive proton-proton (<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>p</mi><mi>p</mi></mrow></math>) collisions at center-of-mass energies of 0.9, 2.36, and 7 TeV, comparing the results with compact muon solenoid (CMS) experimental data on charged-particle pseudorapidity densities and transverse momentum spectra across different pseudorapidity bins, respectively. Our results show good agreement with the CMS data, particularly only using a single set of parameters for all collision energies. This demonstrates that the PACIAE 4.0 model can serve as a reliable tool for systematically studying the physics of NSD <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>p</mi><mi>p</mi></mrow></math> collisions.

China

Zhen Xie

An-Ke Lei

Hua Zheng

Wen-Chao Zhang

Dai-Mei Zhou

Zhi-Lei She

Yu-Liang Yan

Ben-Hao Sa

Pseudorapidity dependence of charged-particle production in nonsingle diffractive <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>p</mi><mi>p</mi></mrow></math> collisions in the PACIAE 4.0 model

We show that a very clear signal of the presence of a strong magnetic field during the early stage of a high-energy heavy-ion collision is provided by the decay of the <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>Z</mi><mn>0</mn></msup></math> into dimuon pairs. We find that the process is highly anisotropic, producing pairs mainly out of plane, as signaled by a negative value of <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>v</mi><mn>2</mn></msub></math>, and leads to an antimuon transverse momentum distribution which peaks at a higher value of the transverse momentum compared to the peak of the muon transverse momentum distribution. We also show that the process does not produce a significant distortion of the <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>Z</mi><mn>0</mn></msup></math> spectral function. The signal can be identified by comparing the dimuon-invariant mass and the individual muon and antimuon spectra produced in semicentral heavy-ion collisions with the corresponding scaled spectra produced in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>p</mi><mo>+</mo><mi>p</mi></mrow></math> collisions at the <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>Z</mi><mn>0</mn></msup></math> peak.

Mexico

Brazil

Alejandro Ayala

Chile

Ana Julia Mizher

Javier Rendón

Asymmetric muon-antimuon emission from <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>Z</mi><mn>0</mn></msup></math> decays: A potential magnetometer in relativistic heavy-ion collisions

We study the internal structure of exotic hadrons, especially focusing on the relation between the compositeness and physical observables. Defined as the probability of finding hadronic molecular components in the wave function, compositeness serves as a quantitative measure of the internal structure of exotic hadrons. We utilize the coupled-channel potential model incorporating both quark and hadron degrees of freedom, which naturally generate the “bare state” responsible for the elementary component as the bound state in the quark channel. The behavior of the compositeness under the variation of the model parameters is investigated by using the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>X</mi><mo>(</mo><mn>3872</mn><mo>)</mo></mrow></math> as an example. In particular, we analyze the associated scattering phase shifts and the bound-state wave functions to discuss the relation between the compositeness and the scattering observables for a shallow bound state. As a phenomenological application of the present framework, the compositeness of the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>X</mi><mo>(</mo><mn>3872</mn><mo>)</mo></mrow><mo>,</mo><mo> </mo><mrow><msub><mi>T</mi><mrow><mi>c</mi><mi>c</mi></mrow></msub><mrow><mo>(</mo><mn>3875</mn><mo>)</mo></mrow></mrow><mo>,</mo><mo> </mo><mrow><msub><mi>D</mi><mrow><mi>s</mi><mn>0</mn></mrow></msub><mrow><mo>(</mo><mn>2317</mn><mo>)</mo></mrow></mrow></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi>D</mi><mrow><mi>s</mi><mn>1</mn></mrow></msub><mrow><mo>(</mo><mn>2460</mn><mo>)</mo></mrow></mrow></math> is discussed.

Japan

Ibuki Terashima

Tetsuo Hyodo

Compositeness and wave function of shallow bound states in relation to scattering observables

We investigate charge-balance functions for pion, kaon, and proton pairs in proton-proton (pp) collisions at <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13</mn></mrow></math> TeV using Monte Carlo models, pythia8, and epos-lhc, with transverse spherocity to classify event topology and charged-particle multiplicity to select system size. Simulations with pythia8 and epos-lhc reveal that balance-function widths in rapidity and azimuthal angle depend on multiplicity and event shape. In pythia8, widths decrease monotonically with multiplicity, consistent with local charge conservation in a fragmentation-dominated scenario. In contrast, the epos-lhc model, especially when using the core corona implementation, exhibits a more intricate response, where the combined effects of hydrodynamic radial flow and longitudinal diffusion result in narrower azimuthal correlations and broader rapidity correlations. These features are characteristic signatures of collective dynamics, similar to those observed in heavy-ion collisions. Events with low spherocity, which are jetlike in nature, exhibit significantly narrower balance-function widths compared to isotropic events with high spherocity, illustrating that event-shape selection provides clear sensitivity to the underlying dynamics of particle production in pp collisions. The species dependence and event-shape sensitivity of the balance-function widths provide information about the hadronization dynamics and collectivity in small systems. These results demonstrate that multidimensional, particle-species-dependent balance-function measurements can disentangle the underlying mechanisms of charge correlations and mediumlike behavior in high-multiplicity pp collisions.

Italy

Subash Chandra Behera

Arvind Khuntia

System-size and event-shape dependence of particle-identified balance functions in proton-proton collisions at <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13</mn></mrow></math> TeV using PYTHIA 8 and EPOS models

We investigate dimuon production in the context of a first-order phase transition in QCD matter using a chiral fluid dynamics model. This approach incorporates nonequilibrium effects such as entropy production and reheating, which emerge during the dynamical evolution through a first-order phase transition. By comparing equilibrium and nonequilibrium scenarios across a range of beam energies (<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msqrt><msub><mi>s</mi><mi>NN</mi></msub></msqrt><mo>=</mo><mn>2.2</mn><mo>–</mo><mn>6.2</mn></mrow></math> GeV), we analyze the resulting invariant mass spectra. Our results reveal a substantial enhancement of dilepton yields in the nonequilibrium scenario, particularly pronounced at lower beam energies, where reheating leads to a prolonged lifetime of the fireball and increased emission. The enhancement persists even after normalizing to pion multiplicities, indicating sensitivity beyond effects of entropy production.

Malaysia

Mohamad Lukman Aidid Mohd Yusoff

Norhasliza Yusof

Hasan Abu Kassim

Germany

Jan Steinheimer

Marcus Bleicher

Thailand

Apiwit Kittiratpattana

Ayut Limphirat

Christoph Herold

Electromagnetic probes as signatures for a first-order QCD phase transition

In this study we examine the impact of the initial stage and dynamical evolution on final-state observables in heavy-ion collisions. For this goal we develop a novel approach, <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>EPOSir</mi><mo>+</mo><mi>PHSDe</mi></mrow></math>, which employs energy-conserving multiple parallel scattering approach, accommodating factorization and saturation (EPOS) initial conditions as the starting point for parton and hadron evolution within the parton-hadron-string dynamics (PHSD) microscopic transport approach. By examining the space-time evolution of matter in this model and comparing to EPOS (which starts with an <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>S</mi></mrow></math>-matrix approach for parallel scatterings for the initial conditions and uses a hydrodynamic evolution for the quark-gluon plasma stage with the UrQMD as afterburner) and PHSD (which starts with primary high-energy <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>N</mi><mi>N</mi></mrow></math> scattering realized via the LUND string model and continues with fully microscopic transport dynamics for strongly interacting partonic and hadronic matter), we identify the key differences in the final particle distributions among the three approaches. Our analysis focuses on rapidity, transverse momentum spectra, and flow harmonics <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>v</mi><mn>2</mn></msub></math> for <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>Au</mi><mo>+</mo><mi>Au</mi></mrow></math> collisions at the invariant energy of <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo>=</mo><mn>200</mn></mrow></math> GeV. We find a dominant influence of dynamical evolution over the initial conditions on the final observables.

France

Mahbobeh Jafarpour

JINR

Vadym Voronyuk

Klaus Werner

Elena Bratkovskaya

Damien Vintache

Disentangling initial-state and evolution effects in heavy-ion collisions using EPOS and PHSD

The early stage of a heavy-ion collision is marked by rapid entropy production and the transition from a gluon saturated initial condition to a plasma of quarks and gluons that evolves hydrodynamically. However, during the early times of the hydrodynamic evolution, the chemical composition of the QCD medium is still largely unknown. We present a study of quark chemical equilibration in the (Q)GP using a novel model of viscous hydrodynamic evolution in partial chemical equilibrium. Motivated by the success of gluon saturated initial condition models, we initialize the QCD medium as a completely gluon dominated state. Local quark production during the hydrodynamic phase is then simulated through the evolution of time-dependent fugacities for each independent quark flavor, with the timescales set as free parameters to compare different rates of equilibration. We present the results of complete heavy-ion collision simulations using this partial chemical equilibrium model, and show the effects on hadronic and electromagnetic observables. In particular, we show that the development of flow is sensitive to the equilibration timescale, providing an empirical way to probe the chemical equilibration of the QCD medium.

United States

Andrew Gordeev

Steffen A. Bass

Berndt Müller

Jean-François Paquet

Quark flavor equilibration of the quark-gluon plasma

The evolution of nuclear excitation in electron-gold (<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>e</mi><mspace width="0.16em"></mspace><mo>+</mo><mspace width="0.16em"></mspace><mi>Au</mi></mrow></math>) collisions at the forthcoming Electron-Ion Collider (EIC) is investigated using the beagle event generator. The EIC's collider kinematics and detector-motivated rapidity selections enable a clear separation, in the laboratory frame, of the dominant reaction stages: hard scattering, intranuclear cascade (INC), and nuclear deexcitation. A systematic study of the event-by-event mean transverse momentum fluctuation observable <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>κ</mi></math> reveals strong sensitivity to the intranuclear-cascade formation time and to nuclear geometry, with only weak dependence on the electron-beam energy. These findings indicate that <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>κ</mi></math> can serve as an exploratory diagnostic for disentangling the cascade and deexcitation stages of nuclear excitation at the EIC. The pronounced sensitivity observed within the beagle framework underscores the model dependence of the present results while at the same time motivating systematic cross-model investigations to establish the broader applicability of <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>κ</mi></math>. The results yield stage-resolved, testable predictions for early EIC measurements.

Niseem Magdy

Tracing the evolution of nuclear excitation at the future Electron-Ion Collider

Using the Monte Carlo <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>HYDJET</mi><mo>+</mo><mo>+</mo></mrow></math> model, we investigate the transverse momentum (<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>p</mi><mi>T</mi></msub></math>) spectra of heavy-flavor hadrons, namely <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>D</mi><mn>0</mn></msup><mo>,</mo><mo> </mo><msup><mover><mi>D</mi><mo>¯</mo></mover><mn>0</mn></msup><mo>,</mo><mo> </mo><msup><mi>D</mi><mo>+</mo></msup><mo>,</mo><mo> </mo><msup><mi>D</mi><mo>−</mo></msup></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi mathvariant="normal">Λ</mi><mi>c</mi></msub></math>, along with the nuclear modification factors of <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>D</mi><mn>0</mn></msup></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>D</mi><mo>±</mo></msup></math> in Au <math xmlns="http://www.w3.org/1998/Math/MathML"><mo>+</mo></math> Au collisions at <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo>=</mo><mn>200</mn></mrow></math> GeV RHIC energy across various centrality bins. This work extends the earlier study by relaxing the assumption of identical chemical and thermal freezeout and by exploring the effect of a higher chemical freezeout temperature relative to thermal freezeout. The study also explores the centrality and mass dependence of the charm enhancement factor (<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>γ</mi><mi>c</mi></msub></math>). Furthermore, we investigate medium-induced energy loss, particle-antiparticle asymmetry, and the role of fragmentation in the hadronization process. The <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>HYDJET</mi><mo>+</mo><mo>+</mo></mrow></math> model, with its default parameters, is unable to reproduce heavy hadron yields due to their early thermal freezeout and initial state production of heavy quarks. Therefore, a systematic tuning of model parameters is performed to improve the overall agreement with experimental data. Additionally, to assess the performance of the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>HYDJET</mi><mo>+</mo><mo>+</mo></mrow></math> model relative to other theoretical approaches, its results are compared with the TAMU, SUBATECH, Torino, and Duke models, for which corresponding simulation data are available. This study shows a decreasing trend in <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>γ</mi><mi>c</mi></msub></math> from central to peripheral collisions. Moreover, <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>γ</mi><mi>c</mi></msub></math> increases with increasing charm-hadron mass. The model approximately reproduces the experimental data of <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>p</mi><mi>T</mi></msub></math> spectra at low and intermediate <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>p</mi><mi>T</mi></msub></math>. However, it overestimates the data at high <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>p</mi><mi>T</mi></msub></math>, indicating a need for improvements in modeling the energy loss of heavy quarks. The nuclear modification factors (<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>R</mi><mrow><mi>A</mi><mi>A</mi></mrow></msub></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>R</mi><mrow><mi>C</mi><mi>P</mi></mrow></msub></math>) for <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>D</mi><mn>0</mn></msup></math> mesons exhibit significant suppression at high <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>p</mi><mi>T</mi></msub></math>. At low <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>p</mi><mi>T</mi></msub><mo>,</mo><mo> </mo><msub><mi>R</mi><mrow><mi>A</mi><mi>A</mi></mrow></msub></math> results show deviations from the data, reflecting limitations in the model where coalescence becomes important. The antiparticle-to-particle ratios are consistent with experimental data, whereas mixed-particle ratios are underestimated, revealing the model's limitation in estimating the baryon-to-meson enhancement.

India

Sunidhi Saxena

Rajiv Gupta

Gauri Devi

Ajay Kumar

Heavy hadron production in <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>Au</mi><mo>+</mo><mi>Au</mi></math> collisions at a center-of-mass energy of <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo>=</mo><mn>200</mn></mrow></math> GeV

We propose a new method to investigate the existence and location of the conjectured high-temperature critical point of strongly interacting matter via contours of constant entropy density. By approximating these lines as a power series in the baryon chemical potential <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>μ</mi><mi>B</mi></msub></math>, one can extrapolate them from first-principle results at zero net-baryon density, and use them to locate the quantum chromodynamics (QCD) critical point, including the associated first-order and spinodal lines. As a proof of principle, we employ currently available continuum-extrapolated lattice data from the Wuppertal-Budapest collaboration to find a critical point at a temperature and a baryon chemical potential of <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi>T</mi><mi>c</mi></msub><mo>=</mo><mn>114.3</mn><mo>±</mo><mn>6.9</mn></mrow></math> MeV and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi>μ</mi><mrow><mi>B</mi><mo>,</mo><mi>c</mi></mrow></msub><mo>=</mo><mn>602.1</mn><mo>±</mo><mn>62.1</mn></mrow></math> MeV, respectively, at expansion order <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi mathvariant="script">O</mi><mo>(</mo><msubsup><mi>μ</mi><mi>B</mi><mn>2</mn></msubsup><mo>)</mo></mrow></math>. We advocate for a more precise determination of the required expansion coefficients via lattice QCD simulations as a means of pinpointing the location of the critical endpoint in the phase diagram of strongly interacting matter.