abstract

The history of the evolution of questions of interest in the study of relativistic \(pA\) and \(AA\) collisions is presented. It covers the period from 1930 to 2005, however emphasis is placed on the pre-RHIC era.

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Since the last Quark Matter conference in Wuhan in 2019, the ALICE Collaboration has produced a remarkable number of new results, studying all colliding systems available at the LHC. This document contains only a partial collection of the wealth of results presented at the 2022 edition of Quark Matter in Kraków.

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This report highlights some of the new results presented in 13 talks and 8 posters by the ATLAS Collaboration at the Quark Matter 2022 Conference. Particular emphasis is given to the most recent results regarding the production of jets, quarkonia, heavy-flavor quarks, collective effects, and photon-induced processes in ultra-peripheral collisions.

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The LHCb experiment has a unique kinematic coverage for heavy-ion physics with its collider and fixed-target configurations. We report on the latest LHCb measurements constraining QCD phenomena.

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In these proceedings, an overview of recent results from the HADES experiment will be given, including electromagnetic probes, hadron anisotropy, and resonance production. References to strangeness results are also provided.

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Despite the challenges of pandemic the years 2020–21 were quite successful for STAR. We completed the Beam Energy Scan program phase 2 and installed the forward upgrade with which STAR finished data-taking for polarized \(p+p\) collisions at 510 GeV. In this contribution, we discuss STAR results on five different topics that were presented in twenty one parallel talks, forty-seven posters, and two flash talks at the Quark Matter 2022 conference.

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PHENIX has performed an extensive study on the evolution of medium effects from small to large systems. PHENIX has continued searching for Quark–Gluon Plasma (QGP) in small systems by measuring collectivity, modification of light hadron and quarkonia production, and jet substructure. In large systems, detailed studies on the property of the QGP have been done using direct photon, \(\pi ^{0}\)-hadron correlation, heavy-flavor electron, and \(J/\psi \) flow with large statistics of data collected in 2014. This report covers new results from the PHENIX experiment in various collision systems.

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The NA61/SHINE experiment is a fixed-target, broad acceptance facility at the CERN SPS. This contribution summarizes the most recent results from the strong interactions NA61/SHINE programme and presents news on the detector upgrade in preparation for the future data taking. The strong interactions programme consists in a two-dimensional scan in beam momentum (from 13\(A\) to 150\(A\)/158\(A\) GeV/\(c\), \(\sqrt {s_{NN}}\) from 5.1 to 17.3 GeV) and system size (\(p+p\), Be\(+\)Be, Ar\(+\)Sc, Xe\(+\)La reactions). The experiment searches for the second-order critical end-point in the temperature versus baryo-chemical potential phase diagram and studies the properties of the onset of deconfinement discovered by its predecessor, NA49 at the CERN SPS. The presented results include \(K/\pi \) multiplicity ratios as a function of energy and system size, singly and multi-strange hadron production in \(p+p\) reactions, multiplicity and net-charge fluctuations measured by higher order moments in \(p+p\), Be\(+\)Be, and Ar\(+\)Sc collisions, proton and charged hadron intermittency in Ar\(+\)Sc and Pb\(+\)Pb reactions, HBT measurements in Ar\(+\)Sc, and collective electromagnetic effects in Ar\(+\)Sc collisions.

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A possible resolution of the early thermalisation puzzle is provided by the notion of far-from-equilibrium attractors which arise due to the specific kinematics of heavy-ion collisions. Attractors appear in a wide variety of dynamical models and it is plausible that they also occur in QCD. The physical implications of these observations depend on how robust this effect is when typically made symmetry restrictions are relaxed. I briefly review this line of research and its perspectives.

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A central question in high-energy nuclear phenomenology is how the geometry of the quark–gluon plasma (QGP) formed in relativistic nuclear collisions is precisely shaped. In our understanding of such processes, two features are especially crucial for the determination of the QGP geometry, respectively, the nucleon size and the energy deposition scheme. This contribution reports on the (circular) evolution of such features in state-of-the-art model incarnations of heavy-ion collisions over the past seven years. Ideas for future directions of investigation are pointed out.

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I present an overview of recent developments in the microscopic description of the quark–gluon plasma. I will concentrate on the medium-induced emission and transverse momentum broadening. These are two key ingredients of the theory of jet modifications in the QCD medium and of the kinetic theory used for transport and thermalisation. The main focus is on the progress towards a better understanding of theory and its uncertainties.

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Out of the many exciting results obtained with the lattice approach to QCD under extreme conditions, I discuss a few selected items related to chiral symmetry: the chiral condensate as an approximate order parameter, meson screening masses, and masses of baryons and mesons, including \(D_{(s)}\) mesons, when approaching the crossover from the hadronic side.

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In this contribution, I review the connection between compact stars and high-baryon density matter, focusing on astrophysical observables for deconfinement to quark matter. I discuss modern ingredients, repositories, and constraints for the neutron-star equations of state. Finally, I draw comparisons between dense and hot matter created in neutron-star mergers and heavy-ion collisions and the possibility of quantitatively establishing a link between them.

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The phase diagram of the QCD matter can be explored in heavy-ion collisions by measuring event-by-event fluctuations of conserved charges. In these proceedings, we will introduce the known issues for measurements of higher-order fluctuations, and discuss how we have overcome them. We will then report on some of the recent experimental results and their interpretations. Finally, the future prospects of the fluctuation measurements will be discussed.

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The experimental status is reviewed on the search for the chiral magnetic effect (CME) in relativistic heavy-ion collisions. Emphasis is put on background contributions to the CME-sensitive charge correlation measurements and their effects on data interpretation.

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The hot and dense matter formed in relativistic heavy-ion collisions at the Relativistic Heavy-Ion Collider (RHIC) and Large Hadron Collider (LHC) is termed quark–gluon plasma (QGP). The evolution of the medium is characterized by non-trivial velocity and vorticity fields, resulting in the polarization of the produced particles. The spin polarization, being sensitive to the hydrothermal (flow velocity and temperature) gradients, is unique compared to conventional observables that are sensitive to the hydrothermal fields only. Hence, the recent measurements of global and local hyperon spin polarization and vector meson spin alignment by the LHC and STAR collaborations provide a unique opportunity to probe the QGP substructure with finer details.

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We review recent progress in relativistic hydrodynamics, discussing causal and stable first-order hydrodynamics, known as BDNK theories, hydrodynamic attractors, as well as hydrodynamics near the chiral critical point and spin hydrodynamics.

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A significant goal of high-energy nuclear collisions is to determine the Quantum Chromodynamics phase diagram for the strongly interacting matter. The most experimentally accessible way to characterize the QCD phase diagram is to scan it in temperature and the baryon chemical potential. The hadronic matter exists in a state where quarks and gluons are confined in composite particles. At high-energy densities, QCD predicts a phase transition from a hadronic gas to a state of deconfined matter — the quark–gluon plasma. In a hot and dense state, QCD matter is melted into quarks, and the strong interaction becomes dominant. The QCD-based models predict a first-order phase transition and the existence of a critical point at a higher \(\mu _B\). However, the exact locations of the first-order phase transition and the critical point are still unknown. In order to study the QCD phase structure experimentally, the Beam Energy Scan program at RHIC was proposed. In these proceedings, the current status of the BES program at RHIC is presented.

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Electromagnetic probes are not affected by hadronization and provide direct information about the space-time evolution of high-energy nucleus–nucleus collisions. In particular, the measurement of thermal radiation from the quark–gluon plasma and the extraction of an effective medium temperature belong to the key objectives in heavy-ion physics. We provide a brief tour of current results and an outlook on future measurements.

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The penetrating nature of electromagnetic probes makes them an ideal candidate to study properties of the Quark–Gluon Plasma (QGP). A selection of recent developments in the theory and phenomenology of electromagnetic probes is discussed, with an emphasis given towards how these probes can be used to constrain QGP transport coefficients. A Bayesian treatment of electromagnetic radiation, similar to the one of soft hadronic observables and jets, is suggested as a path towards imposing more stringent constraints on various transport coefficients of the QCD medium.

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Ultraperipheral collisions (UPC) of heavy ions and protons offer a highly interesting opportunity to study various aspects of QED and (non-) perturbative QCD. Both photonuclear (\(\gamma A\)) and two-photon (\(\gamma \gamma \)) interactions are measured in the experiments at RHIC and LHC. In these proceedings, we discuss recent physics results on topics that can be studied in UPC, including nuclear shadowing, nuclear structure, precision QED, and searches for physics beyond the Standard Model.

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An overview of selected recent theoretical developments of the production and hadronization of heavy flavor hadrons in nuclear collisions is presented. The presentation consists of three parts. The first part concerns the production of charm hadrons in high-energy proton–proton collisions. The second part describes the theoretical advancements in the determination of heavy-quark diffusion coefficient and hadronization mechanisms in the quark–gluon plasma (QGP) created in relativistic heavy-ion collisions. The third part reports on recent developments from modeling of heavy quarkonia production in heavy-ion collisions. While the first part serves as the baseline study for charm-hadron production in QGP, a close and quantitative connection between open- and hidden-charm transport in QGP as emerging from discussions in the second and third parts is revealed and highlighted.

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The recently discovered abundance of heavy hadrons with more than three valence quarks remains poorly understood. Measurements of these exotic hadrons and their interactions with the QCD medium provide a new avenue to investigate their properties. Additionally, the production of hadrons with more than three quarks presents new testing grounds for models of particle transport and coalescence in hadron collisions. These proceedings will explore new data on exotic hadrons, various models of their properties, and give an outlook on future measurements in heavy-ion collisions.

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The progress in constraining proton and nuclear parton distribution functions is briefly summarised. Some persistent uncertainties are pointed out and recent experimental advancements highlighted.

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This contribution discusses the perspectives for heavy-ion physics with the experiments at the LHC. After reviewing the perspectives of LHC for the upcoming runs, the installed and planned upgrades of the four large experiments are presented. For the topics of major interest of heavy-ion physics, the experimental requirements and the physics prospects are discussed.

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Isolated photons and dijets measurements in small collision systems, i.e. , \(pp\) and \(pA\), probe the initial state of the collision, providing the opportunity to constrain PDFs, test pQCD predictions, and probe cold nuclear matter effects. In addition, dijet measurements are sensitive to interactions of partons with the medium produced in Pb–Pb collisions that induce modifications in jet properties. Therefore, measurements in small collision systems also offer a baseline for Pb–Pb collision measurements. In this article, we present the measurement of isolated photons and dijets in small collision systems, \(pp\) and \(p\)–Pb by ALICE. Isolated photons are measured in \(pp\) collisions at \(\sqrt s = 8\) and 13 TeV and in \(p\)–Pb collisions at \(\sqrt {s_{NN}} = 5.02\) TeV, down to \(p_{\mathrm {T}} = 10\) GeV/\(c\), extending previous measurements at these centre-of-mass energies down to small \(x\sim 10^{-3}\). The dijet invariant mass is measured in \(pp\) and \(p\)–Pb collisions at \(\sqrt {s_{NN}} = 5.02\) TeV within the range from \(80\) to \(150\) GeV\(/c^2\), probing a region where medium effects are expected to be strong.

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We investigate the existence of far-from-equilibrium attractors in moments of the one-particle distribution function within the framework of a 3+1D Boltzmann transport approach at fixed \(\eta /s\). We compare our results for a conformal and non-conformal gas for different values of \(\eta /s\) and different initial anisotropy.

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We establish the existence of a far-from-equilibrium attractor in the weakly-coupled gauge theory undergoing 0\(+\)1d Bjorken expansion which goes beyond the energy-momentum tensor to the detailed form of the one-particle distribution function. We then demonstrate that the dynamics can be rescaled at intermediate times and represented by universal exponents. Finally, we assess different procedures for reconstructing the full one-particle distribution function from the energy-momentum tensor along the attractor and discuss implications for the freeze-out procedure used in the phenomenological analysis of ultra-relativistic nuclear collisions

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We use a novel formulation of the relaxation time approximation to consistently calculate the bulk and shear viscosity coefficients using QCD-inspired energy-dependent relaxation times and phenomenological thermal masses obtained from fits to lattice QCD thermodynamics. The matching conditions are conveniently chosen to simplify the computations.

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In these proceedings, we present the measurements of neutron skin thickness and nuclear deformation using isobar \(^{96}_{44}\)Ru+\(^{96}_{44}\)Ru and \(^{96}_{40}\)Zr+\(^{96}_{40}\)Zr collisions at \(\sqrt {s_{_{NN}}}=200\) GeV by the STAR detector. The significant deviations from unity of the isobar ratios of elliptic flow \(v_{2}\), triangular flow \(v_{3}\), mean \(p_{\rm T}\) fluctuations \(\langle \delta p_{\rm T}^{2}\rangle /\langle p_{\rm T}\rangle ^{2}\), and asymmetric cumulant \({\rm ac}_{2}\{3\}\) indicate large differences in their quadrupole and octuple deformations. The significant deviations of the isobar ratios of produced hadron multiplicity \(N_{\rm ch}\), mean transverse momentum \(\langle p_{\rm T}\rangle \), and net charge number \(\Delta Q\) indicate a halo-type neutron skin for the Zr nucleus, much thicker than for the Ru nucleus, consistent with the nuclear structure calculations. We discuss how we extract the neutron skin thickness, the symmetry energy slope parameter, and deformation parameters from data.

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We employ the QCD kinetic theory, including next-to-leading (NLO) order corrections in coupling constant, to study the evolution of weakly coupled non-Abelian plasmas towards thermal equilibrium. For two characteristic far-from-equilibrium systems with either under- or over-occupied initial conditions, the NLO corrections remain well under control for a wide range of couplings, and the overall effect of NLO corrections is a reduction in the time required for thermalization.

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We employ an effective kinetic description to study the space-time dynamics and development of the transverse flow of small and large collision systems. By combining analytical insights in the few interactions limit with numerical simulations at higher opacity, we are able to describe the development of transverse flow from very small to very large opacities, realised in small and large collision systems. Surprisingly, we find that deviations between kinetic theory and hydrodynamics persist even within the limit of very large interaction rates, which can be attributed to the presence of the early pre-equilibrium phase.

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We determine the likelihood distribution for the model parameters describing the event-by-event fluctuating proton geometry at small \(x\) by performing a Bayesian analysis within the Color Glass Condensate framework. The exclusive \(J/\psi \) production data from HERA is found to constrain the model parameters well, and we demonstrate that complementary constraints can be obtained from simulations of Pb+Pb collisions at the LHC.

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We report on the measurements of spin alignment (\(\rho _{00}\)) for \(K^{*0}\), \(\overline {K^{*0}}\), \(K^{*+}\), and \(K^{*-}\) vector mesons in the RHIC isobar collisions (Zr+Zr and Ru+Ru) at \(\sqrt {s_{NN}} = 200\) GeV. We observe the first non-zero spin alignment for \(K^{*\pm }\) in heavy-ion collisions. The \(K^{*\pm }\) \(\rho _{00}\) is about 3.9\(\sigma \) larger than that of \(K^{*0}\). The observed difference and the ordering between \(K^{*\pm }\) and \(K^{*0}\) are surprising and require further inputs from theory. When comparing the isobar and Au+Au collisions, no significant system size dependence in \(K^{*0}\) \(\rho _{00}\) is observed within uncertainties.

abstract

Polarization and spin-alignment measurements represent an important tool for the understanding of particle-production mechanisms occurring in proton–proton collisions. When considering heavy-ion collisions, quarkonium polarization could also be used to investigate the characteristics of the hot and dense medium (quark–gluon plasma) created at LHC energies. In ALICE, this observable was extracted for the first time in Pb–Pb collisions and a significant difference with respect to a corresponding measurement in \(pp\) collisions by the LHCb was found. This discrepancy could be related to the modification of the \(J/\psi \) feed-down fractions, due to the suppression of the excited charmonium states in the QGP, but also to the contribution of the regenerated \(J/\psi \) in the low transverse momentum region. Moreover, it has been hypothesized that quarkonium states could be polarized by the strong magnetic field, generated in the early phase of the evolution of the system, and by the large angular momentum of the medium in non-central heavy-ion collisions. This kind of information can be assessed by defining an ad hoc reference frame where the quantization axis is orthogonal to the event plane of the collision. In this contribution, the recent result of \(J/\psi \) polarization with respect to the event plane in Pb–Pb collisions at \(\sqrt {s_{NN}} = 5.02\) TeV will be presented. The \(p_{\mathrm {T}}\)-differential measurement is performed at forward rapidity (\(2.5 \lt y \lt 4\)) with the ALICE muon spectrometer and the results will be shown for different centrality classes. The preliminary measurement of the \({\mit \Upsilon }(1S)\) and \(D^{*+}\) polarization in \(pp\) collisions at \(\sqrt {s} = 13\) TeV as a function of the transverse momentum will also be discussed.

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In this work, we present a new method to measure the global spin polarization of hyperons produced in non-central relativistic heavy-ion collisions which accounts for relativistic effects due to the frame dependence of global orbital angular momentum direction defining the spin quantization axis. Using the new correlator, we estimate the resulting numerical corrections to be reaching 10 percent for the most energetic particles.

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We study the important, yet widely overlooked, role of gluons for spin transport with a connection to local parity violation in quark–gluon plasmas. We extend the newly developed quantum kinetic theory for relativistic fermions to the case coupled with non-Abelian chromo-electromagnetic fields and employ this formalism to investigate the spin polarization of quarks under dynamically generated color fields in near-equilibrium quark–gluon plasmas. It is found that the spin polarization could be induced by parity-odd correlators of color fields, which may dominate over collisional effects at weak coupling. Our result provides with a possible explanation for the spin alignment of vector mesons measured in high-energy nuclear collisions and alludes to the connection with local parity violation.

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We briefly review the thermal model predictions related to the longitudinal spin polarization of \({\mit \Lambda }\) hyperons emitted from a hot and rotating hadronic medium produced in non-central relativistic heavy-ion collisions.

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The spin polarization measurements of particles emitted in heavy-ion collisions have opened the possibility for new phenomenological investigations of spin physics in relativistic fluids. The theoretical predictions of global polarization are in agreement with the data, but consistent discrepancies stand out for the local polarization. We show that the covariant theory of relativistic quantum fluids at the local equilibrium implies an additional, non-dissipative contribution to the spin polarization vector, which is proportional to the thermal shear, which has been previously overlooked. This additional contribution, together with an improved approximation in the expansion of the local equilibrium density operator, restores the quantitative agreement between the theoretical predictions and the experimental data.

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In these proceedings, we present our recent prediction on the local net Lambda polarization to search for the baryonic spin Hall effect (SHE) at RHIC BES energies. The baryonic SHE is induced by the gradients of baryon chemical potential, which leads to local polarization separation between baryons and anti-baryons. Based on hydrodynamic simulations with the spin Cooper–Fryer formula, we propose to use \(P^{\rm net}_{2,y}\) and \(P^{\rm net}_{2,z}\), the second Fourier coefficients of net spin polarization to quantify this baryonic SHE. Future experimental observation of their non-trivial signatures could strongly support the existence of the baryon SHE in hot and dense QCD matter.

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Charge-dependent azimuthal anisotropy Fourier coefficients are measured with two- and three-particle correlations in \(p\)Pb and PbPb collisions. The difference between positively- and negatively-charged particles for the second-order two-particle, \(v_2\{2\}\), and three-particle, \(v_2\{3\}\), coefficients for both \(p\)Pb and PbPb, and third-order two-particle coefficient, \(v_3\{2\}\), for PbPb, are presented. The observed results are challenging the hypothesis that attributes the charge-dependent azimuthal correlations in heavy-ion collisions to the chiral magnetic effect. In addition, the two-particle electric charge balance function is used as a probe to study the charge creation mechanism in high-energy heavy-ion collisions, for the first time in CMS. The balance function is constructed using like and unlike charged-particle pairs. The width of the balance function, both in relative pseudo-rapidity and relative-azimuthal angle, increases from more central collisions to peripheral ones. Narrowing and widening of these widths indicate late and early hadronization, respectively.

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We calculate the Wigner function for charged spin-1 particles in inhomogeneous classical electromagnetic fields, going to first order in a power series in \(\hbar \). The Boltzmann equation for the scalar distribution function obtained from this formalism agrees with previous calculations for spin‑1/2 particles. In particular, we recover a Mathisson force of twice the magnitude, correctly reflecting the higher dipole moment of vector mesons. Evolution equations for vector and tensor degrees of freedom are obtained and global equilibrium is discussed.

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In heavy-ion collisions with energies ranging from \(\sqrt {s_{NN}}=7.7\) GeV to 5.02 TeV, the observation of the global hyperon polarization, \(P_H\), has revealed the existence of large vorticities perpendicular to the reaction plane due to the system’s orbital angular momentum. This discovery has posed new questions: does \(P_H\) grow at \(\sqrt {s_{NN}}\lesssim 7.7\) GeV, indicating hydrodynamic behavior in the hadron gas? Can high-precision measurements of the suggested \(P_{\bar {{\mit \Lambda }}}\)–\(P_{\mit \Lambda }\) indicate a large late-stage magnetic field sustained by the QGP? Can further studies of vorticity driven by collective flow, leading to a longitudinal spin polarization, \(P_{z}\), shed light on the discrepancies between measurements and model predictions? To answer these questions, and more, we present here recent results of integrated and differential measurements of \(P_H\) and \(P_{z}\) in recent high-statistics data sets acquired by the STAR Collaboration. We show the integrated and differential \(P_H\) in Au+Au collisions at \(\sqrt {s_{NN}}=19.6\) and \(27\) GeV, as well as at the fixed-target collision energies of \(\sqrt {s_{NN}}=3\) and \(7.2\) GeV. Furthermore, Ru+Ru and Zr+Zr collisions allow for the study of the system-size dependence of \(P_H\) and \(P_{z}\), as well as \(P_{z}\) relative to the higher-order event-plane angles.

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In these proceedings, we discuss the recent precision measurements of charge separation difference between Ru+Ru and Zr+Zr collisions at \(\sqrt {s_{NN}}=200\) GeV by the STAR Collaboration. The measurements indicate that the magnitude of the difference in the charge separation attributable to the magnetic fields between the two systems is smaller than previously expected. We also present charge separation measurements on the Chiral Magnetic Effect search from the RHIC BES-II experiment using the Event Plane Detectors (EPD) from Au+Au collisions at \(\sqrt {s_{NN}}=27\) GeV.

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In these proceedings, we present higher-order cumulants of proton multiplicity distributions of the fixed-target (FXT) run in Au+Au collisions at \(\sqrt {s_{NN}}=3.0\) GeV. The cumulant ratios are presented as a function of centrality and collision energy. The proton cumulant ratio \(C_4/C_2\) is consistent with fluctuations driven by baryon number conservation and indicates an energy regime dominated by hadronic interactions. These data imply that the QCD critical point could exist at energies higher than 3 GeV if created in heavy-ion collisions.

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It is shown how to embed a critical point in a smooth background equation of state so as to yield the critical exponents and critical amplitude ratios expected of a transition in the same universality class as the liquid–gas phase transition and the 3D Ising model. There are only two independent critical exponents; the relations \(\alpha + 2\beta + \gamma = 2\) and \(\beta (\delta - 1) = \gamma \) arise automatically, as does a new relation between the two critical amplitudes. The resulting equation of state has parameters which may be inferred by hydrodynamic modeling of heavy-ion collisions in the Beam Energy Scan II at the Relativistic Heavy Ion Collider.

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Recent progress of a general deterministic approach to the non-Gaussian fluctuation dynamics is reviewed, with an emphasis on the derivation of the fluctuation evolution equations and their phenomenological implication in heavy-ion collision experiments.

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We show that the values of the first three cumulants of the baryon-number distribution can be used to calculate the isothermal speed of sound and its logarithmic derivative with respect to the baryon-number density. We discuss applications of this result to heavy-ion collision experiments and address possible challenges, including effects due to baryon-number conservation, differences between proton and baryon cumulants, and the influence of finite-number statistics on fluctuation observables in both experiment and hadronic transport simulations. In particular, we investigate the relation between quantities calculated in infinite, continuous matter, and observables obtained in simulations using a finite number of particles.

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In these proceedings, we present the first measurements of identified charged hadrons in Au\(+\)Au collisions at \(\sqrt {s_{NN}}=3.0\) GeV. Results of baryon stopping, associated production of kaons, and the Coulomb potential of stopped protons are presented. Physics implications of these measurements are discussed.

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We explore jet–medium interactions at various scales in high-energy heavy-ion collisions using the JETSCAPE framework. The physics of the multi-stage modeling and the coherence effect at high virtuality is discussed through the results of multiple jet and high-\(p_{\mathrm {T}}\) particle observables, compared with experimental data. Furthermore, we investigate the jet–medium interaction involved in the hadronization process.

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We propose a new model for a homogeneous description of hadron–hadron, hadron–nucleus, and nucleus–nucleus collisions — the Gluon Exchange Model (GEM). While technically it can be regarded as a generalization of the Dual Parton Model by Capella and Tran Thanh Van, it is fundamentally based on the number of exchanged color octets (gluons) and significantly extends the Fock space of states available for the participating protons and nucleons. In proton–proton collisions, we provide an exact description of the final-state proton and neutron spectrum. Unlike the original DPM, GEM successfully describes the proton diffractive peak at high rapidity. In proton–nucleus reactions, we propose a statistical scheme for the process of soft color octet (gluon) exchange, based on the assumption that the probability to form an effective diquark will be equal for all the allowed quark pairs. The effective diquark can be formed by two valence, one valence and one sea, or by two sea quarks. Consequently, we calculate the probabilities for the different color configurations, involving diquarks of valence–valence, valence–sea, and sea–sea types. These probabilities depend on the number of exchanged gluons, which results in increasing baryon stopping as a function of the number \(N\) of proton–nucleon collisions in the nucleus. As such, the process of transport of baryon number down to low rapidities appears to be governed by the emergence of new color configurations as a function of \(N\) rather than by the energy loss of the original valence diquark.

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A new approach is presented to explore the singularity structure of lattice QCD in the complex chemical potential plane. Our method can be seen as a combination of the Taylor expansion and analytic continuation approaches. Its novelty lies in using rational (Padé) approximants for studying the Lee–Yang edge singularities. We present a calculation of the cumulants of the net-baryon number as a function of a purely imaginary baryon number chemical potential, obtained with highly improved staggered quarks at temporal lattice extent of \(N_\tau =4,6\). We construct various rational function approximations of the lattice data and determine their poles (and roots) in the complex plane. We compare the position of the closest pole to the theoretically expected position of the Lee–Yang edge singularity. At high temperature, we find scaling that is in accordance with the expected power law behavior of the Roberge–Weiss transition, while a different behavior is found for \(T\lesssim 170\) MeV.

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Diffusion wake is an unambiguous part of the jet-induced medium response in high-energy heavy-ion collisions that leads to a depletion of soft hadrons in the opposite direction of the jet propagation. Using a coupled linear Boltzmann transport and hydro model, we identify a valley structure caused by the diffusion wake on top of a ridge from the initial multiple parton interaction (MPI) in the jet–hadron correlation as a function of azimuthal angle and rapidity. This gives rise to the unambiguous signals of the diffusion wake on soft hadrons in the opposite direction of the jets, which are reflected in the depletion in azimuthal angle distribution after subtraction of the contributions from MPI with a mixed-event procedure, and the double-peak structure in the rapidity distribution. We further employ the longitudinal and transverse gradient jet tomography for the first time to localize the initial jet production positions in \(Z/\gamma \)-jet events in which the effect of the diffusion wake is apparent in \(Z/\gamma \)-hadron correlation even without the subtraction of MPI.

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Jets correlated with isolated photons are a promising channel to study jet quenching in heavy-ion collisions, as photons do not interact strongly and therefore constrain the \(Q^2\) of the initial hard scattering. We present the isolated photon–jet correlations measured in Pb–Pb collisions at \(\sqrt {s_{NN}} = 5.02\) TeV by the ALICE Collaboration. We study correlations of isolated photons above 20 GeV/\(c\) with charged-particle jets above 10 GeV/\(c\), reconstructed with the anti-\(k_\mathrm {T}\) algorithm. The correlations probe the lowest jet \(p_\mathrm {T}\) range ever measured at LHC energies, and larger modifications due to the QGP are expected in the lower \(p_\mathrm {T}\) regime.

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The STAR Collaboration presents measurements of semi-inclusive distributions of charged jets recoiling from high transverse energy (\(E_{\mathrm {T}}\)) direct photon and \(\pi ^{0}\) triggers in \(p+p\) and central \(\mathrm {Au}+\mathrm {Au}\) collisions at \(\sqrt {s_{NN}} = 200\) GeV. Jets are reconstructed from charged particles using the anti-\(k_{\mathrm {T}}\) algorithm with jet resolution parameters \(R = 0.2\) and 0.5. The large uncorrelated background in central \(\mathrm {Au}+\mathrm {Au}\) collisions is corrected using a mixed-event technique. This enables a jet measurement extending to low transverse momentum and large \(R\) with well-controlled systematic uncertainties. We present measurements of the jet \(R\) dependence of suppression, intra-jet broadening, and acoplanarity of \(\pi ^{0}+\)jet and \(\gamma _{\mathrm {dir}}+\)jet for trigger \(E_{\mathrm {T}}\) (\(E_{\mathrm {T}}^{\mathrm {trig}}\)) between 9–20 GeV.

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In this work, we introduce both gluon and quark degrees of freedom for describing the partonic cascades inside the medium. We present numerical solutions for the set of coupled evolution equations with splitting kernels calculated for the static, exponential, and Bjorken expanding media to arrive at medium-modified parton spectra for quark- and gluon-initiated jets, respectively. We discuss novel scaling features of the partonic spectra between different types of media. Next, we study the inclusive jet \(R_{AA}\) by including phenomenologically driven combinations of quark and gluon fractions inside a jet. In addition, we have also studied the effect of the nPDF as well as vacuum-like emissions on the jet \(R_{AA}\). Differences among the estimated values of quenching parameter for different types of medium expansions are noted. Next, the impact of the expansion of the medium on the rapidity dependence of the jet \(R_{AA}\) as well as jet \(v_2\) is studied in detail. Finally, we present qualitative results comparing the sensitivity of the time for the onset of the quenching for the Bjorken profile on these observables. All the quantities calculated are compared with the recent ATLAS data.

abstract

QGP, a strongly coupled liquid when viewed at length scales of \({\cal O}(1/T)\), must reveal quark- and gluon-like quasi-particles when probed with sufficiently high momentum transfer, since QCD is asymptotically free. High energy jet partons traversing the droplet of QGP produced in a heavy-ion collision can trigger these high-momentum exchanges with medium constituents and so have the potential to reveal the presence of such quasi-particles, a key step toward the experimental study of the microscopic structure of QGP. We implement this physics within the hybrid strong/weak coupling model which, prior to this work, only accounted for nonperturbative aspects of parton energy loss. Elastic Molière scatterings between partons from a jet shower and medium quasi-particles result in deflection of the propagating jet partons and struck thermal medium partons recoiling at large angles. We discuss the effect of Molière scatterings on some of the most widely used groomed and ungroomed jet substructure observables. Given the large impact on jet observables of the wakes generated by the hydrodynamic response of the QGP fluid as the shower and scattered partons lose energy and momentum to it, as well as the presence of selection biases, finding distinctive signatures of Molière scattering, and hence the presence of quasi-particles in QGP, is a challenge. Toward this end, we emphasize the discovery potential of subjet (jets within jets) distributions.

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Jet quenching, a standard signature of quark–gluon plasma (QGP) formation in which jets lose energy by traversing the medium, comprises a well-studied set of observables in heavy-ion collisions. Significant questions remain, however, concerning the mechanisms driving this phenomenon. Theoretical work that attempts to address these open questions offers the path-length dependence of jet energy loss as one way to better understand the underlying mechanisms of jet quenching. It has proven challenging, however, to derive explicit values for the path-length dependence from experimental data. These proceedings discuss recent results from ALICE that attempt to contribute to our understanding of this phenomenon, including results of event-shape engineered jet spectra, the jet–particle \(v_{2}\), and correlation studies between hard triggers and hadrons.

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Jet quenching is a well-established signature of quark–gluon plasma formation in heavy-ion collisions. Studies of the transverse momentum balance of back-to-back jets, as well as medium-induced modifications to jet shapes and fragmentation functions, provide important experimental constraints on quark–gluon plasma properties. Using a large sample of dijet events from 5.02 TeV lead–lead and proton–proton collisions recorded by the CMS, we study quenching effects differentially with respect to the dijet transverse momentum balance. We use short-range correlations between jets and charged particles to assess medium-induced modifications to jet substructures on each side of the dijet. The path-length-dependent energy loss and energy density fluctuations are also probed using long-range correlations between jets and charged particles.

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The early production of heavy-flavor (HF, charm, and beauty) quarks makes them an excellent probe of the dynamical evolution of quantum chromodynamics (QCD) systems. Jets tagged by the presence of a HF hadron give access to the kinematics of the heavy quarks, and along with correlation measurements involving HF hadrons allow for comparisons of their production, propagation, and fragmentation across different systems. In this contribution, the latest results on HF jets and angular correlations measured with the ALICE detector in \(pp\), \(p\)–Pb, and Pb–Pb collisions from the LHC Run 2 data are reported.

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The charged-particle multiplicity in the transverse region, \(N^{\mathrm {T}}_{\mathrm {ch}}\), which is sensitive to the underlying event, is studied. Measurements of charged-particle production as a function of \(N^{\mathrm {T}}_{\mathrm {ch}}\) in \(pp\), \(p\)–Pb, and Pb–Pb collisions at \(\sqrt {s_{NN}}=5.02\) TeV in the toward, away, and transverse regions are discussed. These regions are defined relative to the track with the largest transverse momentum in the event (\(p_{\mathrm {T}}^{\mathrm {trig}}\)). The activity in the transverse region is subtracted from the activity in the toward and away regions to search for jet-like modifications in small collision systems. The jet-like signals are studied both as a function of \(N^{\mathrm {T}}_{\mathrm {ch}}\) and \(p_{\mathrm {T}}^{\mathrm {trig}}\). Results are compared with two general-purpose Monte Carlo event generators: PYTHIA 8 and EPOS LHC.

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The JETSCAPE Collaboration reports on a new determination of jet transport coefficients in the Quark–Gluon Plasma, using both reconstructed jet and hadron data measured at RHIC and the LHC. The JETSCAPE framework incorporates detailed modeling of the dynamical evolution of the QGP; a multi-stage theoretical approach to in-medium jet evolution and medium response; and Bayesian inference for quantitative comparison of model calculations and data. The multi-stage framework incorporates multiple models to cover a broad range in scale of the in-medium parton shower evolution, with a dynamical choice of model that depends on the current virtuality or energy of the parton. We will discuss the physics of the multi-stage modeling, and then present a new Bayesian analysis incorporating it. This analysis extends the recently published JETSCAPE determination of the jet transport parameter \(\qhat {}\) that was based solely on inclusive hadron suppression data, by incorporating reconstructed jet measurements of quenching. We explore the functional dependence of jet transport coefficients on QGP temperature and jet energy and virtuality, and report the consistency and tensions found for current jet quenching modeling with hadron and reconstructed jet data over a wide range in kinematics and \(\sqrts {}\). This analysis represents the next step in the program of a comprehensive analysis of jet quenching phenomenology and its constraint of properties of the QGP.

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We compute the in-medium jet broadening \(\langle p_\perp ^2 \rangle \) to leading order in energy in the opacity expansion. At leading order in \(\alpha _{\mathrm {s}}\), the elastic energy loss gives a jet broadening that grows with \(\ln E\). The next-to-leading order in \(\alpha _{\mathrm {s}}\) result is a jet narrowing, due to destructive LPM interference effects, that grows with \(\ln ^2 E\). We find that in the opacity expansion, the jet broadening asymptotics are — unlike for the mean energy loss — extremely sensitive to the correct treatment of the finite kinematics of the problem; integrating over all emitted gluon transverse momenta leads to a prediction of jet broadening rather than narrowing. We compare the asymptotics from the opacity expansion to a recent twist-4 derivation of \(\langle p_\perp ^2 \rangle \) and find a qualitative disagreement: the twist-4 derivation predicts a jet broadening while the opacity expansion method predicts a narrowing. Comparison with current jet measurements cannot distinguish between the broadening or narrowing predictions. We comment on the origin of the difference between the opacity expansion and twist-4 results.

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Jets in relativistic heavy-ion collisions (HICs) interact with the quark–gluon plasma (QGP), leading to effects such as the suppression of jet yields and a modification of internal jet structure that are used to measure the properties of the QGP. These proceedings show the inclusive jet nuclear modification factors in Pb–Pb collisions in various centrality classes at \(\sqrt {s_{NN}}=5.02\) TeV recorded with the ALICE detector for resolution parameters up to \(R=0.6\) for momenta down to 40 GeV/\(c\). The analysis utilizes machine learning techniques to correct the large background in HICs, extending the measurement of inclusive jets to lower jet \(p_\mathrm {T}\) and larger \(R\) than previously achieved in HICs at the LHC. A new suite of measurements characterizing groomed jet splittings using both the Soft Drop and Dynamical Grooming algorithms in central and semi-central Pb–Pb collisions will also be presented. The groomed jet radius, \(\theta _{\rm g}\equiv R_{\rm g}/R\), the groomed jet momentum fraction, \(z_{\rm g}\), and the transverse momentum of the groomed splitting, \(k_{\rm T, g}\) are also reported. All measurements are fully corrected through unfolding and compared to various theoretical calculations.

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PHENIX has quantified the modification of jets in heavy-ion collisions due to partonic energy loss in the quark–gluon plasma (QGP) by measuring the distribution of hadrons relative to a trigger particle, such as a high-momentum photon or \(\pi ^0\). These two-particle correlations have revealed that high-momentum hadrons are suppressed, while the yield of low-momentum hadrons is enhanced. This enhancement is the most pronounced at relatively large angles away from the opposing jet axis. More recent analyses have further investigated and quantified these phenomena by studying the yield modification as a function of the azimuthal angle, \(\Delta \phi \). The larger data sets collected by PHENIX in 2014 and 2016 enhance the statistical precision and enable more differential measurements, which provide insight into how the jet’s substructure is modified by the QGP and crucial constraints on models of partonic energy loss and medium response. The latest analyses of \(\pi ^0\)–hadron and direct photon–hadron correlations in Au\(+\)Au collisions measured by PHENIX are presented, and how these results impact our understanding of jet modification and partonic energy loss in the QGP and the medium response to jets is discussed.

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NA61/SHINE is a fixed target experiment at the CERN Super Proton Synchrotron. The main goals of the experiment are to discover the critical point of strongly-interacting matter and to study the properties of the onset of deconfinement. In order to reach these goals, a study of hadron production properties is performed in nucleus–nucleus, proton–proton, and proton–nucleus interactions as a function of collision energy and size of the colliding nuclei. In this article, the new results on identified charged kaon production in the intermediate size system (\(^{40}\)Ar+\(^{45}\)Sc and \(^7\)Be+\(^9\)Be) collisions at the SPS beam momentum range (13 \(A\)–150 \(A\) GeV/\(c\)) will be shown. Additionally, the new measurements of strange mesons (\(K^0_{\mathrm {S}}\)), resonances (\(K^{0*}\)(892), \({\mit \Xi }(1530)^0\), and \(\bar {\mit \Xi }(1530)^0\)) and baryons (\({\mit \Xi }^-\)(1321), \({\mit \Xi }^+\)(1321)) produced in \(p\)+\(p\) interactions are presented.

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Correlations between multiparticle cumulants and mean transverse momentum in proton–proton (\(pp\)), proton–lead (\(p\)Pb), and peripheral lead–lead (PbPb) collisions are presented as a function of charged-particle multiplicity. The data, corresponding to integrated luminosities of 28.6 pb\(^{-1}\) for \(pp\) at \(\sqrt {s}=13\) TeV, 186 nb\(^{-1}\) for \(p\)Pb at \(\sqrt {s_{_{NN}}}=8.16\) TeV, and 0.58 nb\(^{-1}\) for PbPb at \(\sqrt {s_{_{NN}}}=5.02\) TeV, were collected using the CMS detector at the LHC. The two- and four-particle cumulants for the second- and third-order Fourier harmonics are correlated with the mean transverse momentum on an event-by-event basis. Sign changes are observed when using two-particle cumulants in \(pp\) and \(p\)Pb systems. No sign change is observed as pseudorapidity gaps between the two subevents increase. Predictions based on color-glass condensate and hydrodynamic models are compared to the experimental results.

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We investigate the medium evolution in \(p\)+Pb collisions at LHC energy by comparing a non-equilibrium transport approach, PHSD, with a (2+1)D viscous hydrodynamic model, VISHNew, with initial conditions extracted from PHSD. We find that the energy density in PHSD is highly inhomogeneous in the transverse plane during the whole evolution, whereas VISHNew dissolves efficiently the initial spatial irregularities. We perform also a comparison of event topology in the two approaches by means of the transverse spherocity observable. We found that the spherocity distribution in PHSD is slightly shifted towards the isotropic limit with respect to the hydrodynamic case, mainly due to the different descriptions within the two models of the medium produced in small systems. We have applied the spherocity selection to the elliptic flow of charged particles finding that it is predominantly determined by the most jetty events. This finding supports the idea that multi-differential measurements through multiplicity and spherocity are very useful to study final-state observables in ultra-relativistic proton–nucleus collisions.

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These proceedings report on recent experimental searches for jet-quenching effects in \(pp\) collisions at \(\sqrt {s}=13\) TeV. The measurements are based on two jet observables: inclusive jet production and the semi-inclusive yield of jets recoiling from a high-transverse-momentum \((p_{\mathrm {T}})\) hadron. Both measurements are carried out differentially in event multiplicity, which is assumed to bias the size of the collision system. To search for jet quenching effects, the shape of the inclusive jet yield in different multiplicity intervals is compared to the one obtained in minimum bias (MB) events. The increase in selected charged-particle multiplicity causes a rise in the jet yield but only minor changes in the slope of the jet spectrum above 20 GeV/\(c\). In the semi-inclusive analysis, recoil jet acoplanarity is measured for events selected on high multiplicity (HM) and compared to the MB population. A striking modification of the acoplanarity distribution, which is nominally characteristic of jet quenching, is observed in the measured HM population. Its origin is elucidated by comparisons with PYTHIA calculations.

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We present the measurement of two-particle correlations in hadronic \(e^+e^-\) collisions data collected by the Belle detector at KEKB. The clean \(e^+e^-\) collision system is conducive to the unambiguous investigation of the azimuthal anisotropy of final-state charged particles found in various heavy-ion and proton–proton collisions. High-statistics Belle datasets at the center-of-mass energies of \(\sqrt {s} = 10.52\) GeV (\(89.5~\mathrm {fb}^{-1}\)) and 10.58 GeV on the \({\mit \Upsilon }(4S)\) resonance (\(333.2~\mathrm {fb}^{-1}\)) are analyzed. The larger statistics also enable the study of very rare events of the multiplicity distribution tail. Measurements are reported as a function of the charged-particle multiplicity over the full relative azimuthal angle \((\Delta \phi )\) and three units of pseudorapidity \((\Delta \eta )\). Correlation functions calculated in two coordinate systems with respect to different reference axes — the conventional beam axis and the event thrust axis — are measured. The thrust-reference-axis coordinate is the more natural representation for \(e^+e^-\) annihilating into a quark–antiquark pair for providing sensitivity to the color activity emitted transversely to the diquark fragmentation. In this paper, we also present a qualitative understanding of the measured correlation structure based on the Monte Carlo simulations. We will discuss the correlations for jet fragmentation in this low-energy regime and for the special scenario of \(b\bar {b}\) bound state decays.

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The first measurement of anti-\(k_\mathrm {T}\) jets and two-particle angular correlations of charged particles emitted in high energy \(e^+e^-\) annihilation is presented. The archived data at a center-of-mass energy of 91 GeV were collected with the ALEPH detector at LEP between 1992 and 1994. At 91GeV, no significant long-range correlation was observed in either the laboratory coordinate analysis or the thrust coordinate analysis, where the latter is sensitive to a medium expanding transverse to the color string between the outgoing \(q\bar {q}\) pair from \(Z\) boson decays. We also present the first measurement of anti-\(k_\mathrm {T}\) jet energy spectra and substructures compared to various event generators, NLO, and NLL’+\(R\) resummation calculations.

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The creation of fluid-like quark–gluon plasma in small collision systems has been investigated via elliptical azimuthal anisotropy of emitted particles in these interactions. We report on the first measurement of the azimuthal anisotropy for the \({\mit \Upsilon }(1S)\) meson in \(p\)Pb collisions at 8.16 TeV. The dimuons used to reconstruct the \({\mit \Upsilon }(1S)\) meson are coupled with charged hadrons using the long-range two-particle correlation method. The results are discussed in terms of collectivity of bottom quarks.

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The suppression of the \(\psi (2S)\) nuclear modification factor has been seen as a trademark signature of final-state effects in large collision systems for decades. In small systems, deviations of the nuclear modification from unity had been attributed to cold nuclear matter effects until the observation of strong differential suppression of the \(\psi (2S)\) state in \(p/d+A\) collisions, which suggests the presence of final-state effects. In this paper, we present results of \(J/\psi \) and \(\psi (2S)\) measurements in the dimuon decay channel for \(p+p\), \(p+\)Al, and \(p+\)Au collision systems at \(\sqrt {s_{_{NN}}} = 200\) GeV. Key results include the nuclear modification factors \(R_{pA}\) as a function of centrality and rapidity. The measurements are compared with shadowing and transport model predictions, as well as complementary measurements at LHC energies.

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Measurements of quarkonia (heavy quark and antiquark bound states) and open-heavy flavour hadrons in hadronic collisions provide a unique testing ground for understanding quantum chromodynamics (QCD). Although recently there was significant progress, our understanding of hadronic collisions has been challenged by the observation of intriguing effects in high-multiplicity proton–proton (\(pp\)) and \(p\)–Pb collisions, such as collective phenomena. The excellent particle identification, track and decay-vertex reconstruction capabilities of the ALICE experiment are exploited to measure quarkonia as well as open-heavy flavour hadron production at midrapidity while quarkonium measurements are inclusive at forward rapidity. In this contribution, the first measurements of the elliptic flow (\(v_2\)) of \(J/\psi \) in high multiplicity \(pp\) collisions are shown. New measurements of quarkonium and open-beauty hadron production in \(pp\) and \(p\)–Pb collisions are presented, such as the first measurement of the non-prompt \({D}^{*+}\) polarization in \(pp\) collisions at \(\sqrt {s}=13\) TeV. The comparison of results with available models is also discussed.

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Medium modification of particle spectra and the origin of collectivity in small collision systems are widely debated topics in the heavy-ion community. To address these open questions, we propose the study of particle production and collectivity for varying system sizes, Au+Au \(\gt \) Ru+Ru/ Zr+Zr \(\gt \) Cu+Cu \(\gt ~d\)+Au \(\gt \,\gamma \)+Au, available at RHIC using the STAR detector. We present the first measurements of centrality-dependent charged hadron production in isobar (Ru+Ru and Zr+Zr) collisions, including the nuclear modification factors (\(R_{AA}\)) at high transverse momentum (\(p_{\mathrm {T}}\)), and identified particle spectra at low \(p_{\mathrm {T}}\) at mid-rapidity. Combined with existing results from other systems, they probe system-size and collision geometry dependences of the medium modification to particle production. In addition, we present the measurement of particle production and long-range di-hadron correlations in \(\gamma \)+Au events using ultra-peripheral Au+Au collisions at RHIC.

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Using high-statistics data sets generated in (2+1)-flavor QCD calculations at finite temperature, we construct estimators for the radius of convergence from an eighth-order series expansion of the pressure as well as the number density. We show that the estimator for pressure and number density will be identical in the asymptotic limit. In the vicinity of the pseudo-critical temperature, \(T_{\mathrm {pc}}\simeq 156.5\) MeV, we find the estimator of the radius of convergence to be \(\mu _B/T \gtrsim \ 3\) for strangeness-neutral matter. We also present results for the pole structure of the Padé approximants for the pressure at non-zero values of the baryon chemical potential and show that the pole structure of the [4,4] Padé is consistent with not having a critical point at temperatures larger than \(135~\)MeV and a baryon chemical potential smaller than \(\mu _B/T \sim \ 2.5\).

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We apply and extend a novel approach to non-perturbatively estimate the heavy-quark momentum diffusion coefficient \(\kappa \), which is a key input for the theoretical description of heavy quarkonium production in heavy-ion collisions, and is important for the understanding of the elliptic flow and nuclear suppression factor of heavy flavor hadrons. In the heavy-quark limit, this coefficient is encoded in the spectral functions of color-electric and color-magnetic correlators that we calculate on the lattice to high precision by applying gradient flow. In a recent study we have considered quenched QCD at \(1.5\,T_{\mathrm {c}}\), where we performed a detailed study of the lattice spacing and flow time dependence of the color-electric correlator, and, using theoretically well-established model fits for the spectral reconstruction, we estimated the heavy-quark diffusion coefficient. Equipped with the experience obtained in quenched QCD, we estimate \(\kappa \) from 2+1 flavor QCD ensembles at small but finite lattice spacing and flow time without increasing systematic errors significantly.

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I describe how interactions can be included via a model phase shift.

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We study the initial-state momentum correlations and event-by-event geometry in \(p+\)Pb collisions at \(\sqrt {s}=5.02~\rm TeV\) by following the approach of extending the IP-Glasma model to 3D using the JIMWLK rapidity evolution. On examining the non-trivial rapidity dependence of the observables, we find that the geometry is correlated over large rapidity intervals, while the initial-state momentum correlations have a relatively short range in rapidity. Based on our results, we discuss implications for the relevance of both effects in explaining the origin of collective phenomena in small systems.

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The production mechanism of deuterons, which have a binding energy of 2.2 MeV, is a topic of current interest in high-energy heavy-ion collisions. Two of common scenarios are statistical thermal process and coalescence of nucleons. The cumulants of deuteron number and proton–deuteron correlations are sensitive to these physics processes. They are also sensitive to the choice of canonical versus grand canonical ensemble in statistical thermal models. We report on the first measurements of cumulant ratios (up to \(4^{\mathrm {th}}\) order) of the deuteron number and proton–deuteron correlations in Au\(+\)Au collisions at \(\sqrt {s_{NN}} = 7.7\)–200 GeV. Comparisons of the measurements to the thermal model calculations with a grand canonical, canonical ensemble, and the UrQMD model combined with a coalescence mechanism provide key insights into the mechanism of deuteron production in heavy-ion collisions.

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A valuable tool used in the search for QCD’s critical point is the computation of cumulants of conserved charge. Near this point, it is expected a sharp increase in this quantity due to the divergence of correlation lengths. This calculation requires high statistics, which poses a challenge to hydrodynamics simulations, which tend to be computationally expensive. The issue can be ameliorated by means of a procedure called oversampling, i.e. one repeats the Monte Carlo step of the particlization many times for a single hydro event. However, this has the drawback of removing the effects of fluctuations caused during the particlization. We use a toy model to demonstrate a method to compute cumulants (developed originally by Grassi, Hirayama, and Ollitrault) in a scenario where the oversampling procedure is employed and proceed to compute it for several collision energies.

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Fluctuations of conserved charges are important probes to explore a hot and dense medium in relativistic heavy-ion collisions. In this paper, we focus on the experimentally-observed second-order cumulants of baryon number and electric charge at the top RHIC energy. We compare the ratio of these cumulants with the corresponding susceptibility ratio observed in lattice QCD numerical simulations. We show that, if one assumes that the experimental results on the cumulants are thermal, the “temperature” predicted from this comparison is significantly lower than that of the chemical freezeout. We argue that this discrepancy comes from the diffusion and resonance decays. The importance of the acceptance correction of the transverse-momentum cut is also emphasized.

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We analyze the behavior of (net-)proton number cumulants in central collisions of heavy ions across a broad collision energy range by utilizing hydrodynamic simulations. The calculations incorporate essential non-critical contributions to proton fluctuations such as repulsive baryonic core and exact baryon-number conservation. The experimental data are consistent with non-critical physics at collision energies of \(\sqrt {s_{NN}} \geq 20\) GeV. The data from the STAR and HADES collaborations at lower collision energies indicate an excess of (multi-)proton correlations over the non-critical reference. This observation is discussed in the context of different mechanisms, including the possibility of a critical point in the baryon-rich region of the QCD phase diagram.

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Particle flow measurements, which provide evidence of the QGP medium, are a powerful tool to study the QGP evolution in heavy-ion collisions. Using the two-particle correlation technique, the LHCb has observed the ridge structure due to particle flow, in the forward pseudorapidity range of \(2\lt \eta \lt 5\) alongside the leading jet peak in long-range correlations (\(|\Delta \eta |\gt 2\)). This paper will detail the analysis of the ridge structure in \(p\)Pb/Pb\(p\) collisions at \(5\) TeV and the results, which show that the ridge structure is more pronounced in the low transverse momentum region and the high-multiplicity events where the collective flow property of QGP may be significant. This presentation will also include the details of new LHCb analyses to extract the flow harmonics in the forward region.

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We study factorization-breaking coefficients between the momentum-dependent and momentum-averaged flow vectors to probe flow fluctuations caused by the initial-state fluctuations in heavy-ion collision. The coefficients for the flow vector squared and flow magnitude squared could be used for the extraction of flow angle decorrelations. We compare our model results with preliminary experimental data. We also present the predictions for the momentum-dependent correlation between mixed flow harmonics.

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We give predictions of the \(DD^*\) and \(D\bar {D}^*\) correlation functions in high-energy collisions based on the pure hadronic molecule picture of \(T_{cc}^+\) and \(X(3872)\). The potentials of \(DD^*\) and \(D\bar {D}^*\) are fixed based on the empirical data, and the momentum correlation functions of the \(D^0D^{*+}\) and \(D^0\bar {D}^{*0}\) pairs are computed with the coupled-channel effects. Since the pole positions of \(T_{cc}^+\) and \(X(3872)\) are close to the \(D^0D^{*+}\) and \(D^0\bar {D}^{*0}\) thresholds, scattering lengths are large in magnitude and the correlation functions show strong enhancement at small relative momenta. When the compact multiquark components are nonnegligible in \(T_{cc}^+\) and \(X(3872)\), the scattering length and the correlation function will be suppressed. Thus, comparison of the present predictions and the data to be measured in the near future will elucidate the nature of the exotic states.

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The Relativistic Heavy-Ion Collider (RHIC) at Brookhaven is a facility to create and study the strongly interacting Quark–Gluon Plasma (QGP). Higher-order cumulants of the conserved quantities and their ratios are powerful tools to study the properties of QGP and explore the QCD phase structure, such as the critical point and/or the first-order phase transition boundary. In these proceedings, we present the net-proton cumulants and their ratios up to the sixth order as a function of multiplicity using high statistics data of \(^{96}_{40}{\mathrm {Zr}}+^{96}_{40}{\mathrm {Zr}}\) and \(^{96}_{44}{\mathrm {Ru}}+^{96}_{44}{\mathrm {Ru}}\) collisions at \(\sqrt {\mathrm {s}_{_{NN}}}=200\) GeV. The STAR experiment collected two billion events for each colliding system. We compared the multiplicity dependence to the published net-proton cumulants in Au+Au collisions at \(\sqrt {\mathrm {s}_{_{NN}}}= 200\) GeV. In addition, we compared the results to the Lattice QCD, the Hadron Resonance Gas model, and hadronic transport model calculations. The physics implications are discussed.

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In recent years, there has been a significant effort to extract the temperature-dependent shear (\(\eta /s\)) and bulk (\(\zeta /s\)) viscosity over entropy ratios of the quark–gluon plasma from a global comparison of heavy-ion data with results of hydrodynamic simulations. However, anisotropic flow, which is arguably the most sensitive probe of viscosity, is only sensitive to an effective viscosity over entropy ratio, which is obtained by taking a weighted average over the temperature and summing the contributions of shear and bulk. We estimate this effective viscosity using existing first-principles calculations, which give \(0.17\lt (\eta /s)_{\rm eff}\lt 0.21\), and \((\zeta /s)_{\rm eff}\lt 0.08\), implying that the damping of anisotropic flow at the LHC is mostly due to shear viscosity. The values extracted from global data analyses are compatible with these theory predictions.

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Using the two-particle irreducible (2PI) \({\mit \Phi }\)-functional formalism for self-consistent approximations of a linear-\(\sigma \) model for quarks and mesons in and out of equilibrium, the build-up of fluctuations of the net-baryon number during the time evolution of an expanding fireball is studied within a kinetic theory for the order parameter (\(\sigma \) field) and quark distribution functions. Initializing the system with purely Gaussian fluctuations, a fourth-order cumulant is temporarily built up due to the evolution of the \(\sigma \) field. This is counterbalanced, however, by the dissipative evolution due to collisions between quarks, anti-quarks, mesons, and the mean field, depending on the speed of the fireball expansion.

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One important challenge in our field is to understand the initial condition of the QGP and constrain it using sensitive experimental observables. Recent studies show that the Pearson Correlation Coefficient between \({\bm V}_n\) and event-wise mean transverse momentum \([p_{\mathrm {T}}]\), \(\rho _{n}({\bm V}_n,[p_{\mathrm {T}}])\) can probe number and size of sources, nuclear deformation, volume fluctuation, and initial-momentum anisotropy in the initial state of heavy-ion collisions. These proceedings present new, precision measurements of \({\bm V}_n\)–\([p_{\mathrm {T}}]\) correlation in \(^{\mathrm {129}}\mathrm {Xe}+^{\mathrm {129}}\mathrm {Xe}\) and \(^{\mathrm {208}}\mathrm {Pb}+^{\mathrm {208}}\mathrm {Pb}\) collisions for harmonics \(n=2\), 3, and 4 using the ATLAS detector at the LHC. The values of \(\rho _{n}\) show rich and non-monotonic dependence on centrality, \(p_{\mathrm {T}}\) and \(\eta \), reflecting that different ingredients of the initial state impact different regions of the phase space. The ratio of \(\rho _{2}\) between the two systems in the ultra-central region suggests that \({^\mathrm {129}}\mathrm {Xe}\) has large quadrupole deformation and with a significant triaxiality. All current models fail to describe many of the observed trends in the data.

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In these proceedings, we present the measurements of proton, light nuclei, and strange particle with neutral kaons correlation functions in Au\(+\)Au collisions at the BES program and top RHIC energy. The experimental results are compared with model calculations to extract the size of emitting source and the properties of the final-state interactions. The collision energy and centrality dependence of the source size are studied. Further, the implications for the production mechanism of light nuclei are discussed.

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We extend our previously developed \(T\)-matrix framework for the strongly-coupled quark–gluon plasma at vanishing chemical potential (\(\mu _q=0\)) to finite values and utilize it to evaluate various quark number susceptibilities, especially in heavy–light channels. Specifically, we introduce a \(\mu _q\) dependence into the quark propagators and interaction kernel using two new parameters which are fitted to lattice-QCD (lQCD) data for the baryon number susceptibility, \(\chi ^{B}_2\). Without further tuning, we calculate the heavy–light susceptibilities and find that the resulting \(\chi ^{uc}_{11}\) and \(\chi ^{uc}_{22}\) are qualitatively consistent with lQCD data. This agreement suggests that the emergence of broad \(D\)-meson and charm-light diquark bound states in a moderately hot QGP is compatible with lQCD results.

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The energy loss and elliptic flow of heavy quarks provide valuable information for understanding the nature of thermalized quark–gluon plasma. The energy loss of quarks in QGP is expected to depend on their mass. This effect can be investigated by measuring the nuclear modification factors of hadrons made of light and heavy quarks. The coupling between heavy quarks and QGP can also be examined by the measurement of the flow harmonics. The PHENIX experiment measures nuclear modifications and flows of electrons from the semi-leptonic decays of charm and bottom hadrons in Au\(+\)Au collisions at \(\sqrt {s_{NN}} = 200\) GeV. Different suppression of charm and bottom electrons is observed in 0–10% most central Au\(+\)Au collisions. We report on the nuclear modification of charms and bottoms, and discuss the \(p_\mathrm {T}\) dependence and centrality dependence of the heavy-quark energy loss in QGP.

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The first measurements for the rapidity-odd directed flow of \({\mit \Xi }\) and \({\mit \Omega }\) in Au+Au collisions at \(\sqrt {s_{NN}}=27\) and 200 GeV are reported. The coalescence sum rule is examined with various combinations of hadrons where all constituent quarks, such as \(\km \), \(\pbar \), \(\al \), \(\ph \), \(\ks \), \(\om \), and \(\op \) are produced. For such combinations, a systematic violation of the sum rule is observed with increasing difference in the electric charge and the strangeness content of the combinations. Measurements are compared with the calculations of A Multi-Phase Transport (AMPT) model and Parton–Hadron String Dynamics (PHSD) model with electromagnetic (EM) field. The PHSD model with EM field agrees with the measurements within uncertainties.

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We report on the measurement of charmonia in both peripheral and ultraperipheral PbPb collisions recorded by the LHCb detector. The measurement of \(J/\psi \) in ultraperipheral PbPb collisions provides unique opportunities to study the low-\(x\) gluons constituent of the Pb nuclei, while the precise measurement of the low-\(p_{\mathrm {T}}\) \(J/\psi \) confirms coherent production in hadronic collisions.

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We report on the measurements of low-\(p_{\mathrm {T}}\) \(e^{+}e^{-}\) and \(\mu ^{+}\mu ^{-}\) pairs produced in noncentral Au+Au collisions at \(\sqrt {s_{NN}} = 54.4\) GeV and \(\sqrt {s_{NN}} = 200\) GeV at STAR. The measured yields can be well described by the lowest-order EPA-QED calculations for both types of lepton pairs. The \(\sqrt {\langle p_{\mathrm {T}}^{2}\rangle }\) of \(e^{+}e^{-}\) pairs exhibits collision energy dependence, with a hint of possible final-state effects. The low-\(p_{\mathrm {T}}\) \(J/\psi \) spectra in isobaric collisions (\(^{96}_{44}\)Ru\(+^{96}_{44}\)Ru, \(^{96}_{40}\)Zr\(+^{96}_{40}\)Zr) at \(\sqrt {s_{NN}} = 200\) GeV are also measured. Photoproduced \(J/\psi \) are found to be sensitive to the charge of the colliding nuclei, but not to the details of the nuclear form factor or the impact parameter.

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With a unique geometry covering the forward rapidity region, the LHCb detector provides unprecedented kinematic coverage at low Bjorken-\(x\) down to \(10^{-5}\) or lower. The excellent momentum resolution, vertex reconstruction, and particle identification allow for precision measurements down to very low hadron transverse momentum. In this contribution, the latest studies of the relatively unknown low-\(x\) region are reported, including recent measurements of charged and neutral light hadron production in proton–lead and proton–proton collisions. Comparisons to various theoretical model calculations are also discussed. Finally, prospects for future measurements are outlined.

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Diffractive photoproduction of \(J/\psi \) vector mesons is studied at the LHC with the ALICE detector in \(p\)–Pb and Pb–Pb ultra-peripheral collisions (UPCs), where the Pb ions act as powerful sources of quasi-real photons. In this contribution, the first measurement at the LHC of dissociative photoproduction of \(J/\psi \) off protons is presented; this process is sensitive to quantum fluctuations of the structure of the target at the subnucleon level. In addition, cross sections for the exclusive channel and for continuum dimuon production at small masses were obtained in the same kinematic region. This latter process probes our simultaneous understanding, in a new kinematic region, of the photon flux emitted by protons and by lead ions. The transverse momentum dependence of \(J/\psi \) photoproduction on lead targets in Pb–Pb collisions at midrapidity, which is sensitive to the gluonic structure of Pb in the impact-parameter plane, is also presented. The measurement of \(J/\psi \) photoproduction off hadrons sheds light onto the initial state of QCD targets and provides important constraints on the initial conditions used in hydrodynamical models of heavy-ion collisions.

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We discuss the sensitivity of the \(\gamma \gamma \to \tau ^+\tau ^-\) process in ultraperipheral Pb+Pb collisions at LHC energies to the anomalous magnetic moment of \(\tau \) lepton (\(a_\tau \)). We derive the corresponding cross sections considering semi-leptonic decays of both leptons in the fiducial volume of ATLAS and CMS detectors. The expected limits on \(a_\tau \) with the existing Pb+Pb dataset are better than the DELPHI experimental limit and can be further improved by a factor of two at the High Luminosity LHC. Our analysis provides a novel theoretical probe of the \(\tau \) anomalous magnetic moment using ultraperipheral heavy-ion collisions at the LHC. The verification of our theoretical results with the latest ALICE and CMS experimental data will be also presented.

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It is likely that a change from nuclear to quark matter (QM) in the neutron star (NS) cores is a continuous crossover. Importantly, the ab initio estimates of the equations of state (EOSs) in the low-density nuclear region and in the high-density QCD region are both soft, and so the EOS at the intermediate-density region must inevitably be stiff to support massive NSs as observed by the Shapiro time delay. Thus, the first-order phase transition that tends to make the EOS softer is severely constrained. The possible impact of the presence of QM on the gravitational wave signals has already been discussed under an assumption of a strong first-order phase transition for the QM onset. Here, we show that the gravitational wave signals are sensitive enough to detect the QM cores even if the transitional change is a smooth crossover. The early gravitational collapse is induced mainly by rapid softening, not by a discontinuity from the first-order phase transition.

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I discuss why the state-of-the art perturbative QCD calculations of the equation of state at large chemical potential that are reliable at asymptotically high densities constrain the same equation of state at neutron-star densities. I describe how these theoretical calculations affect the EOS at lower density. I argue that the ab initio calculations in QCD offer significant information about the equation of state of the neutron-star matter, which is complementary to the current astrophysical observations.

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We consider the parity doublet model for nucleonic and delta matter to investigate the structure of neutron stars. We show that it is possible to reconcile the multi-messenger astronomy constraints within a purely hadronic equation of state (EoS), which accounts for the self-consistent treatment of the chiral symmetry restoration in the baryonic sector. We demonstrate that the characteristics of the EoS required by the astrophysical constraints do not necessarily imply the existence of a hadron–quark phase transition in the stellar core.

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Given the lack of empirical evidence of weakly interacting dark matter, it is reasonable to look to other candidates such as a confining dark sector with a similar number of particles as the Standard Model. Twin Higgs mirror matter is one such a model that is a twin of the Standard Model with particle masses 3–6 times heavier than the Standard Model that solves the hierarchy problem. This generically predicts mirror neutron stars, degenerate objects made entirely of mirror nuclear matter. We find their structure using a realistic equation of state from the crust (nuclei) to core (relativistic mean-field model) and scale the particle masses using lattice QCD results. We find that mirror neutron stars have unique signatures that are detectable via gravitational waves and binary pulsars, that provides an intriguing possibility for probing dark matter.

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Based on a recently developed relativistic density functional approach to color-superconducting quark matter and a novel quark–hadron transition construction which phenomenologically accounts for the effects of inhomogeneous pasta phases and quark–hadron duality, we construct a class of hybrid equations of state applicable at the regimes typical for compact star astrophysics and heavy-ion collisions. We outline that early quark deconfinement is a notable consequence of strong diquark pairing providing a good agreement with the observational data and driving the trajectories of the matter evolution during the supernova explosions toward the regimes typical for the compact star mergers and heavy-ion collisions.

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In this contribution, the final measurements of the centrality dependence of the nuclear modification factor (\(R_{AA}\)) of non-prompt \(D^0\) in Pb–Pb collisions at \(\sqrt {s_{NN}}\) = 5.02 TeV will be presented. These measurements provide important constraints to the mass dependence of in-medium energy loss and hadronisation of the beauty quark. The \(p_{\rm T}\)-integrated non-prompt \(D^0\) \(R_{AA}\) will be presented for the first time and will be compared to the prompt \(D^0\) one. This comparison will shed light on possible different shadowing effects between charm and beauty quarks. In addition, the first measurements of non-prompt \(D_s^+\) production in central and semi-central Pb–Pb collisions at \(\sqrt {s_{NN}}\) = 5.02 TeV will be discussed. The non-prompt \(D_s^+\) measurements provide additional information on the hadronisation of beauty quarks and the production yield of \(B_s^{0}\) mesons. Finally, the first measurement of non-prompt \(D\)-meson elliptic flow in Pb–Pb collisions at \(\sqrt {s_{NN}}\) = 5.02 TeV will also be discussed. These measurements can constrain the degree of thermalisation of beauty quarks in the hot and dense QCD medium.

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Evidence for the production of top quarks in heavy-ion collisions is reported in a data sample of lead–lead collisions recorded in 2018 by the CMS experiment at a nucleon–nucleon center-of-mass energy of \(\sqrt {s_{_{NN}}} = 5.02\) TeV, corresponding to an integrated luminosity of \(1.7\pm 0.1\) nb\(^{-1}\). Top quark pair (\(t\bar {t\,}\)) production is measured in events with two opposite-sign high-\(p_{\mathrm {T}}\) isolated leptons (\(\ell ^\pm \ell ^\mp =\,e^{+} e^{-},\,\mu ^{+} \mu ^{-}\), and \(e^{\pm } \mu ^{\mp }\)). We test the sensitivity to the \(t\bar {t}\) signal process by requiring or not the additional presence of \(b\)-tagged jets, and hence demonstrate the feasibility to identify top quark decay products irrespective of interacting with the medium (bottom quarks) or not (leptonically decaying \(W\) bosons). To that end, the inclusive cross section (\(\sigma _{t\bar {t}}\)) is derived from likelihood fits to a multivariate discriminator, which includes different leptonic kinematic variables with and without the \(b\)-tagged jet multiplicity information. The observed (expected) significance of the \(t\bar {t}\) signal against the background-only hypothesis is 4.0 (5.8) and 3.8 (4.8) standard deviations, respectively, for the fits with and without the \(b\)-jet multiplicity input. After event reconstruction and background subtraction, the extracted cross sections are \(\sigma _{t\bar {t}} = 2.03 ^{+0.71}_{-0.64}\) and \(2.54 ^{+0.84}_{-0.74}~\mu \)b, respectively, which are lower than, but still compatible with, the expectations from scaled proton–proton data as well as from perturbative quantum chromodynamics predictions. This measurement constitutes the first crucial step towards using the top quark as a novel tool for probing strongly interacting matter.

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Predictions are presented within the framework of the statistical hadronization model for integrated yields of bottomonia in Pb–Pb collisions at the LHC. We investigate the centrality dependence of \({\mit \Upsilon }\) production and provide predictions for a large set of still-unmeasured open-beauty hadrons.

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In this contribution, the nuclear modification factor and azimuthal anisotropy of prompt charm mesons and baryons in Pb–Pb collisions at \(\sqrt {s_{NN}}=5.02\) TeV by the ALICE Collaboration are presented. Heavy quarks are a very suitable probe to investigate the quark–gluon plasma (QGP) produced in heavy-ion collisions, since they are mainly produced in hard-scattering processes and hence in shorter timescales compared to the QGP. Measurements of charm-hadron production in nucleus–nucleus collisions are, therefore, useful to study the properties of the in-medium charm-quark energy loss via the comparison with theoretical models. Models describing the heavy-flavour transport and energy loss in a hydrodynamically-expanding QGP require also precise modelling of the in-medium hadronisation of heavy quarks, which is investigated via the measurement of prompt \({D_s^+}\) mesons and \({\mit \Lambda }_{c}^{+}\) baryons.

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Owing to their different binding energies, bottomonia are particularly useful probes to understand the thermal properties of the quark–gluon plasma (QGP) created in relativistic heavy ion collisions. Previously, the CMS Collaboration measured the sequential suppression of the \({\mit \Upsilon }(1S)\), \({\mit \Upsilon }(2S)\), and \({\mit \Upsilon }(3S)\) states in PbPb collisions. However, the \({\mit \Upsilon }(3S)\) yield was excessively low, thus allowing us to report only statistical upper limits. In this contribution, we report a detailed study of the measurement of excited bottomonium states with improved analysis technique and high-statistics data that enables us to observe the \({\mit \Upsilon }(3S)\) meson in \(AA\) collisions for the first time. The result provides a comprehensive picture of the three \({\mit \Upsilon }\) states in PbPb collisions.

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In this contribution, we present the latest measurements of \(D^0\), \(D^+\), and \(D_s^+\) mesons together with the final measurements of \({\mit \Lambda }_{c}^+\), \({\mit \Xi }_{c}^{0,+}\), \({\mit \Sigma }_{c}^{0,++}\), and the first measurement of \({\mit \Omega }_{c}^0\) baryons performed with the ALICE detector at midrapidity in \(pp\) collisions at \(\sqrt {s}=5.02\) and \(\sqrt {s}=13\) TeV. Recent measurements of charm-baryon production at midrapidity in small systems show a baryon-to-meson ratio significantly higher than that in \(e^+e^-\) and \(e^-p\) collisions, suggesting that the fragmentation of charm is not universal across different collision systems. Thus, measurements of charm-baryon production are crucial to study the charm-quark hadronization in a parton-rich environment like the one produced in \(pp\) collisions at the LHC energies. Furthermore, the recent \({\mit \Lambda }_{c}^+/D^0\) yield ratio, measured down to \(p_\mathrm {T}=0\) in \(p\)–Pb collisions will be discussed. The measurement of charm baryons in \(p\)-nucleus collisions provides important information about a possible additional modification of hadronization mechanisms, on cold nuclear matter effects, and on the possible presence of collective effects that could modify the production of heavy-flavour hadrons. Finally, the first measurements of charm fragmentation fractions and charm production cross section at midrapidity per unit of rapidity will be shown for \(pp\) and \(p\)–Pb collisions using all measured single-charm ground-state hadrons.

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Partons in heavy-ion collisions interact strongly with the Quark–Gluon Plasma (QGP), and hence have their energy and shower structure modified compared to those in a vacuum. Theoretical calculations predict that the radiative energy loss, which is the dominant mode of energy loss for gluons and light quarks in the QGP, is suppressed for heavy quarks at low transverse momenta (\(p_\mathrm {T}\)). At RHIC energies, lower-energy jets closer to the charm quark mass are more accessible and could provide key insight into the understanding of the mass dependence of parton energy loss. We report on the first measurements of the \(D^{0} (c\bar {u})\) meson tagged jet \(p_\mathrm {T}\) spectra and the \(D^{0}\) meson radial profile in jets reconstructed from Au+Au collisions at \(\sqrt {s_{NN}} = 200 \text { GeV}\), collected by the STAR experiment.

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In recent years, a significant theoretical effort has been made towards a dynamical description of quarkonia inside the Quark–Gluon Plasma (QGP), using the open quantum systems formalism. In this framework, one can get a real-time description of a quantum system (here the quarkonium) in interaction with a thermal bath (the QGP) by integrating out the bath degrees of freedom and studying the system reduced density matrix. We investigate the real-time dynamics of a correlated heavy quark–antiquark pair inside the QGP using the novel coupled quantum master equations derived from the first QCD principles. The equations are solved numerically in 1D to lessen computing costs and are used for the first time to gain insight into the dynamics in both a static and evolving medium following a Björken-like temperature evolution with several initial conditions.

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We present the first NLO pQCD study of coherent exclusive \(J/\psi \) photoproduction in ultraperipheral heavy-ion collisions (UPCs) at the LHC. Taking the generalized parton distributions (GPDs) in their forward limit, as parton distribution functions (PDFs), we quantify the NLO contributions in the rapidity-differential cross section, show that the real part of the amplitude must not be neglected, study the gluon and quark contributions, chart the scale-choice and PDF uncertainties, and compare the NLO results with LHC and HERA data. We show that the scale dependence is significant but a scale choice can be found with which we reproduce the 2.76 and 5.02 TeV UPC data. In particular, we show that the process is clearly more sensitive to the nuclear quark PDFs than thought before.

abstract

Measurements of the correlations of the final-state heavy flavor hadrons are of great interest since they provide information about the initial collision geometry and its fluctuation. More importantly, those measurements could reveal the mass dependence of parton energy loss and quark diffusion in the Quark–Gluon Plasma (QGP). In this paper, we report on the first measurement of the azimuthal anisotropy of nonprompt \(D^0\) in PbPb collisions at \(\sqrt {s_{_{NN}}}=5.02\) TeV. The elliptic (\(v_2\)) and triangular (\(v_3\)) coefficients are performed as functions of \(D^0\) transverse momentum \(p_{\mathrm {T}}\), in three centrality classes. Compared to the results from promptly produced \(D^0\), the nonprompt \(D^0\) \(v_2\) flow coefficients are systematically lower. However, those results have a similar dependence on \(p_{\mathrm {T}}\) and centrality. A non-zero \(v_3\) coefficient of the nonprompt \(D^0\) is seen in PbPb data. We also present the first azimuthal angular correlation measurement between jets and \(D^0\) mesons in \(pp\) and PbPb collisions. The jet–\(D^0\) correlation measurement is performed using jets with \(p_{\mathrm {T}} \gt 60\) GeV/\(c\) and \(D^0\) mesons with \(4\lt p_{\mathrm {T}} \lt 20\) GeV/\(c\). In PbPb collisions at 5.02 TeV, compared to the \(pp\), the \(D^0\) distribution hints at the diffusion of charm quarks in the medium, created in heavy-ion collisions. The results could provide new constraints on the mechanism of the heavy quark diffusion and energy loss in the QGP.

abstract

Charmonium production is a direct probe of the quark–gluon plasma (QGP), a deconfined state of nuclear matter formed in heavy-ion collisions. For \(J/\psi \), a bound state of \({c}\bar {c}\) quarks, its (re-)generation within the QGP or at the phase boundary, is found to be the dominant production mechanism at low transverse momentum (\(p_{\mathrm {T}}\)) and in central Pb–Pb collisions at the LHC energies. The relative production of the \(\psi (2S)\) excited state with respect to the \(J/\psi \) is one possible discriminator between the two different regeneration scenarios. In addition, the non-prompt component of \(J/\psi \) production from \(b\)-hadron decays allows one to access the interaction of beauty quarks inside the QGP down to low \(p_{\mathrm {T}}\). In these proceedings, we present, for the first time, results on the \(\psi (2S)\)-to-\(J/\psi \) double ratio in Pb–Pb collisions at forward rapidity and \(\sqrt {s_{NN}} = 5.02\) TeV with respect to a new \(pp\) reference with an improved precision compared to the earlier publications. The combined Run 2 data set of ALICE allows the extraction of a signficant \(\psi (2S)\) signal in central Pb–Pb collisions at forward rapidity down to zero transverse momentum. The \(\psi (2S)\) nuclear modfication factor \(R_{AA}\) as a function of \(p_{\rm T}\) and centrality will also be shown, as well as the inclusive \(J/\psi \) \(R_{AA}\) at forward rapidity. At midrapidity, the inclusive, prompt and non-prompt \(J/\psi \) \(R_{AA}\) as a function of centrality and \(p_{\mathrm {T}}\) will be presented, based on the full Run 2 statistics. The extraction of the non-prompt \(J/\psi \) fraction extends other LHC measurements down to very low \(p_{\rm T}\) and its precision is improved signficantly compared to previous ALICE publications. Results will be compared with available theoretical model calculations.

abstract

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

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We obtain the first measurement of \(J/\psi \) elliptic flow at RHIC energies in forward rapidity using data from the PHENIX detector and applying an event plane method. The dataset used contains 19 billion events from the PHENIX experiment’s Run 14 Au\(+\)Au dataset at \(\sqrt {s_{NN}}=200\) GeV. PHENIX has measured a \(J/\psi \) \(v_2\) in a centrality range of 10–\(60\%\) that is consistent with zero. Taken together with the results from LHC, the measurement of \(v_2\), which is consistent with zero, may indicate that \(J/\psi \) production by coalescence is not significant at forward rapidity at RHIC energy.

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We present some results that describe the properties of the glasma phase that exists at very early times after a relativistic heavy-ion collision. We discuss the isotropization of the glasma, the Fourier coefficients of the momentum flow, and the momentum broadening of a hard probe traversing the glasma.

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We study the far-off-equilibrium dynamics of a Bjorken expanding non-conformal system within kinetic theory and hydrodynamics. We show that, in contrast to the conformal case, neither shear nor bulk viscous pressure relax quickly to a non-equilibrium attractor. In kinetic theory, an early-time, far-from-equilibrium attractor exists for the scaled longitudinal pressure, driven by the rapid longitudinal expansion of the medium. Second-order dissipative hydrodynamics fails to accurately describe this attractor, but a modified anisotropic hydrodynamic formulation reproduces it and provides excellent agreement with kinetic theory.

abstract

The fast development of quantum technologies over the last decades has offered a glimpse into a future where the quantum properties of multi-particle systems might be more fully understood. In particular, quantum computing might prove crucial to explore many aspects of high-energy physics inaccessible to classical methods. In this paper, we will describe how one can use digital quantum computers to study the evolution of QCD jets in quark–gluons plasmas. We construct a quantum circuit to study single-particle evolution in a dense QCD medium. Focusing on the jet quenching parameter \(\hat q\), we present some early numerical results for a small quantum circuit. Future extensions of this strategy are also addressed.

abstract

Collisional broadening in QCD plasmas leads to the emission of medium-induced radiation, which governs the energy loss of highly energetic particles or jets. While recent studies have obtained non-perturbative contributions to the collisional broadening kernel \(C(b_\bot )\) using lattice simulation of the dimensionally reduced long-distance effective theory of QCD, Electrostatic QCD (EQCD), so far all phenomenological calculations of jet quenching rely on perturbative determinations of the collisional broadening kernel. By matching the short-distance behavior of the lattice extracted EQCD broadening kernel, we determine the fully matched QCD broadening kernel non-perturbatively. We present results for the collisional broadening kernel in impact parameter (\(C_{\rm QCD}(b_\bot )\))) and momentum space (\(C_{\rm QCD}(q_\bot )\)), and employ them to determine the rates of medium-induced radiation in infinite and finite size QCD plasmas. By contrasting our results with leading and next-to-leading order perturbative determinations as well as various approximations of the splitting rates employed in the literature, we investigate the effect of the non-perturbative determination of \(C_{\rm QCD}(q_\bot \)) on medium-induced radiation rates.

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Measurements of direct photons can provide valuable information on the properties and dynamics of the quark–gluon plasma (QGP) by comparing them to model calculations that describe the whole evolution of the system created in heavy-ion collisions, from the initial hard scattering to the pre-equilibrium, QGP, and hadronic phases. In the ALICE experiment, photons can be reconstructed either by using the calorimeters or via conversions in the detector material. The photon conversion method benefits from an excellent energy resolution and is able to provide direct photon measurements down to transverse momenta of \(p_{\mathrm {T}} = 0.4\) GeV/\(c\). For Hanbury-Brown and Twiss (HBT) correlation studies, the detector setup can be exploited to combine a conversion photon with a calorimeter photon, such that near-zero opening angles are measured. In this contribution, we present the first measurements of direct photon production in Pb–Pb collisions at \(\sqrt {s_{NN}}=5.02\) TeV by ALICE, including direct photon spectra from central to peripheral events. The latest results of the first analysis of photon HBT correlations at the LHC are shown as well.

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Light-by-light (LbyL) scattering, \(\gamma \gamma \to \gamma \gamma \), is a rare Standard Model (SM) process, also proposed as a sensitive channel to study physics beyond the SM. In these proceedings, we perform a statistical combination of existing \(\gamma \gamma \to \gamma \gamma \) cross section measurements at the LHC with the aim of checking the consistency with different SM predictions. Using a simplified set of assumptions, we find the averaged result of \(115 \pm 19\) nb, consistent with SM predictions within two standard deviations. For the first time, we also consider the contribution from the \(\eta _b(1S)\) meson production to the diphoton invariant mass distribution.

abstract

Dielectrons are a unique tool to study the space-time evolution of the hot and dense matter created in ultrarelativistic heavy-ion collisions. They are produced by a variety of processes during all stages of the collision with negligible final-state interactions. At low invariant mass (\(m_{ee}\)), thermal radiation from the hot hadron gas (HG) contributes to the spectrum while at larger \(m_{ee}\), thermal radiation from the quark–gluon plasma (QGP) carries information about the early temperature of the medium. The latter is nevertheless dominated by a large background of correlated heavy-flavour (HF) hadron decays affected by energy loss and flow in the medium. At very low \(m_{ee}\) (\(m_{ee} \rightarrow 0\)), the fraction of direct photons, including thermal contributions, can be extracted from the dielectron spectrum as a function of transverse momentum (\(p_{\mathrm {T},ee}\)). In proton–proton (\(pp\)) collisions, such measurement serves as a fundamental test for perturbative QCD calculations and a baseline for the studies in heavy-ion collisions. We report on the latest ALICE results on dielectron studies in Pb–Pb and \(pp\) collisions at \(\sqrt {s_{NN}} =5.02\) TeV and \(\sqrt {s}= 13\) TeV, respectively. The results are compared to the expected dielectron yield from known hadronic sources and predictions for thermal radiation from the medium. The production of direct photons in the different colliding systems including high-multiplicity (HM) \(pp\) collisions is discussed.

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We compute the spectra of bremsstrahlung photons for different stopping scenarios which give rise to different initial charge-rapidity distributions. In light of novel experimental opportunities that may arise with a new heavy-ion detector ALICE-3 at the CERN LHC, we discuss how to discriminate between these stopping scenarios and how to disentangle bremsstrahlung photons from other photon sources.

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Due to its forward coverage, the LHCb can probe the valence quark distributions of protons and nuclei at small and large Bjorken-\(x\) with high precision. These proceedings present new LHCb measurements of \(Z\)-boson production in association with charm jet in the forward region of proton–proton collisions and \(Z\)-boson production in proton–lead collisions. \(Z+\)charm-jet production could be sensitive to a valence-like intrinsic-charm component in the proton wave function. The measurements of \(Z\) production in proton–lead collisions provide new constraints on the partonic structure of nucleons inside nuclei. Comparisons between the results and calculations with parton distribution functions are also discussed.

abstract

Electroweak bosons, \(W^{\pm }\) and \(Z^{0}\), are massive weakly-interacting particles insensitive to the strong interaction. Therefore, they are unique probes in \(pp\) and heavy-ion collisions, and provide a medium-blind probe of the initial state of the heavy-ion collision. In the ALICE experiment, the production of \(W^{\pm }\) and \(Z^{0}\) is studied by exploiting their semileptonic decay channels in a wide rapidity region. In this contribution, the results in \(pp\) collisions at \(\sqrt {s}= 13\) TeV, \(p\)–Pb collisions at \(\sqrt {s_{NN}}= 8.16\) TeV, and Pb–Pb collisions at \(\sqrt {s_{NN}}= 5.02\) TeV are reported.

abstract

PHENIX has used the versatility of RHIC to map out low-\(p_{\mathrm {T}}\) direct photon production as a function of collision system size and beam energy. For systems with a size corresponding to a \({\mathrm {d}}N_{\mathrm {ch}}/{\mathrm {d}}\eta \) larger than 20–30, we observe a large yield of direct photons, a large azimuthal anisotropy with respect to the reaction plane, and a characteristic centrality dependence of \({\mathrm {d}}N_{\gamma }/{\mathrm {d}}y \propto ({\mathrm {d}}N_{\mathrm {ch}}/{\mathrm {d}}\eta )^{\alpha }\), with \(\alpha \sim 1.2\). In these proceedings, we will present new results from Au\(+\)Au collisions at \(\sqrt {s_{NN}} = 39\), 62.4, and 200 GeV. After subtracting the prompt photon component, the inverse slope for the \(p_{\mathrm {T}}\) range from 1–2 GeV/\(c\) is 250 MeV/\(c\), but increases to about 400 MeV/\(c\) for the range from 2 to 4 GeV/\(c\). Within the experimental uncertainty, there is no indication of a system-size dependence of the inverse slope. Furthermore, the system-size dependence of the yield, expressed through the power \(\alpha \), remains independent of \(p_{\mathrm {T}}\) over the entire observed range from 1 to 6 GeV/\(c\). Like the large yield and azimuthal anisotropy, these features, while qualitatively consistent with the emission of thermal photons from the quark–gluon plasma, elude a quantitative description through theoretical model calculations.

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Photons resulting from jet–medium interactions offer the opportunity of studying the evolving quark distribution in a heavy-ion collision. The spectra of jet–medium photons are presented within the JETSCAPE framework for two different energy loss models, MARTINI and CUJET. Jet-medium photons can contribute significantly to the spectrum of direct photons in the intermediate \(p_{\mathrm {T}}\) range.

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We present a comprehensive analysis of photon production at RHIC and the LHC, proposing radiative hadronization as an additional photon source in high-energy heavy-ion collisions. For the thermal photon, we perform relativistic viscous hydrodynamic calculation with event-by-event fluctuations.

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In this work, we present preliminary results of HADES on the dielectron analysis of 4.5 billion Ag+Ag collisions ((0–40)% centrality) at a centre-of-mass energy of \(\sqrt {s_{NN}} = 2.55\) GeV. The obtained dielectron signal spectrum is compared to a simulated hadronic cocktail and nucleon–nucleon reference spectra revealing a strong in-medium contribution quantified by the dielectron excess ratio \(R_{AA}\). The average temperature of the collision system can be extracted from the slope of the in-medium contribution. In a momentum differential analysis, we observe modifications of the dielectron signal shape in the \(\omega \)–\(\rho \) invariant mass region.

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We report on the production and azimuthal anisotropy measurements of strange and multi-strange hadrons at STAR BES energies. The \({\mit \Lambda }/K^0_s\) ratio is reported at 3 GeV and observed to increase faster with transverse momentum than that at higher energies. The number of constituent quark (NCQ) scaling of \(v_2\) has been studied at 19.6 GeV (BES-II). The NCQ scaling holds for particles and anti-particles, which can be considered as evidence of partonic collectivity. The production of \(K^{*0}\) resonance is also reported for 7.7–39 GeV (BES-I) and the \(K^{*0}/K\) ratio suggests that hadronic re-scattering dominates over regeneration in central \(A\)+\(A\) collisions. Using the \(K^{*0}/K\) ratio, we also report on the lower limit of hadronic phase lifetime \(( t_{\mathrm {kin}}-t_{\mathrm {chem}})\).

abstract

In this proceedings contribution, the qualitative effect of a net baryochemical potential dependence of the shear viscosity to entropy density ratio \(\eta /s\) in hybrid approach simulations is investigated. The influence of a net baryochemical potential dependence of the shear viscosity over entropy ratio on the observables of heavy-ion collisions has been subject of only few investigations in hydrodynamic simulations. In this work, a generalized \(\eta /s\)(\(T,\mu _B\)) is tested within the hybrid approach SMASH-vHLLE-hybrid, combining the hadronic transport approach SMASH and the (3+1)D viscous hydrodynamic code vHLLE. It is shown that the proposed parameterization approximates the shear viscosity in the late stage non-equilibrium hadronic transport stage.

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We present the first lattice QCD results of the second-order fluctuations of, and correlations among net-baryon number, electric charge, and strangeness in (2+1)-flavor lattice QCD in the presence of a background magnetic field with physical pion mass \(m_{\pi }=135\) MeV. To mimic the magnetic field strength produced in the early stage of heavy-ion collision experiments, we use 6 different values of the magnetic field strength up to \( \sim 10\, m_{\pi }^2\). We find that the correlations between baryon number and electric charge along the transition line are substantially affected by magnetic fields in the current \(eB\) window, which could be useful for probing the existence of a magnetic field in heavy-ion collision experiments.

abstract

Collisions of small systems at RHIC exhibit a significant suppression of the nuclear modification factor \(R_{xA}\) of jets and high-momentum neutral pions in events with large event activity. This suppression is accompanied by an enhancement of \(R_{xA}\) in events with low event activity. Since event activity is commonly interpreted as a measure of the centrality of the collisions, these results call into question any interpretation of the suppression in central collisions that invokes energy loss in a QGP produced small systems. In this contribution, we will compare prompt photon to \(\pi ^0\) production measured by PHENIX in \(d+\)Au collision at \(\sqrt {s}=200\) GeV to demonstrate that the apparent centrality dependence is not related to a nuclear modification of hard scattering processes, but likely due to deviations from the proportionality of event activity and centrality in the underlying standard Glauber model calculations. Furthermore, we will use prompt photon production in \(d+\)Au relative to \(p+p\) collisions to empirically determine the effective number of binary collisions \(N_{\mathrm {coll}}\) of a given event sample. We find that for all event selections, except for those with the highest event activity, \(R_{xA}\) of \(\pi ^0\) is consistent with unity. By comparing \(p+\)Au and \(d+\)Au collisions, we will investigate the significance of the remaining suppression of high-\(p_{\mathrm {T}}\) \(\pi ^0\) production in events with high event activity.

abstract

The second-order (\(v_{2}\)) and the third-order (\(v_{3}\)) Fourier coefficients which describe the azimuthal anisotropy of prompt and nonprompt \(J/\psi \) and prompt \(\psi (2S)\) mesons are measured in PbPb collisions at 5.02 TeV. The \(v_{2}\) and \(v_{3}\) values are extracted using the scalar product method. The measured \(v_{2}\) values for the prompt \(J/\psi \) mesons are larger than those for nonprompt \(J/\psi \) mesons. No significant nonzero \(v_{3}\) values for both prompt and nonprompt \(J/\psi \) mesons, reported for the first time in heavy-ion collisions, are found. The prompt \(\psi (2S)\) meson \(v_{n}\) values are reported also for the first time.

abstract

Measurements of longitudinal flow decorrelation for charged particles in Zr\(+\)Zr and Ru\(+\)Ru (isobar) collisions at \(\sqrt {s_{NN}} = 200\) GeV and Au\(+\)Au collisions at \(\sqrt {s_{NN}} = 19.6\), 27 and 54.4 GeV using the STAR detector are presented. The third-order flow decorrelation is stronger than the second order one. The second-order flow decorrelation shows a strong centrality dependence, while the third-order results show a weak dependence. Comparing with Au\(+\)Au collisions at \(\sqrt {s_{NN}} = 27\) and 54.4 GeV, both the second- and third-order flow decorrelations show obvious energy dependence. In addition, the correlation coefficient \(\rho (v_{n}^{2},[p_{\mathrm {T}}])\) is also measured in Au\(+\)Au collisions at \(\sqrt {s_{NN}} = 19.6\)–200 GeV. No obvious energy dependence is observed for \(\rho (v_{n}^2,[p_{\mathrm {T}}])\). These results provide significant constraints on the initial-state fluctuations.

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The equations of multicomponent relativistic second-order dissipative fluid dynamics from the Boltzmann equations for a reactive mixture of \(N_{\rm {spec}}\) particle species with \(N_q\) intrinsic quantum numbers such as electric charge, baryon number, and strangeness are presented. We discuss the “single-fluid” description of a multicomponent fluid, which consists of \(4+N_q\) conservation laws closed by \(6+3N_q\) equations of motion for the dissipative quantities in the \((10+4N_q)\)-moment approximation.

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The STAR Collaboration has successfully completed an upgrade of the forward detector system located between \(2.5 \lt \eta \lt 4.0\). This upgrade comprises a Forward Calorimeter System, which contains an Electromagnetic Calorimeter and Hadronic Calorimeter, and a Forward Tracking System which consists of a Forward Silicon Tracker and Forward small-strip Thin Gap Chambers. The forward detector upgrade has excellent detection capability for neutral pions, photons, electrons, jets, and charged hadrons. A combination of soft and hard probes collected during 2023–25 will be used to probe the QGP’s microstructure and will enable a unique forward physics program via the collection of high statistics Au+Au, \(p\)+Au, and \(pp\) data at \(\sqrt {s_{NN}}=200\) GeV. With the extended acceptance and the enhanced statistics, STAR will be positioned to perform correlation studies in heavy-ion collisions, e.g. , the pseudorapidity dependence of azimuthal correlations and the pseudorapidity dependence of global hyperon polarization. The STAR forward detector upgrade will also enable an extensive suite of measurements probing the quark–gluon structure of heavy nuclei. In this article, we will present the current status of the forward detector system and discuss its performance during data taking with cosmic-ray and \(pp\) collisions at \(\sqrt {s_{NN}}=510\) GeV during the 2022 RHIC run.

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The LHCb experiment at CERN is a forward spectrometer with a unique heavy-ion physics programme exploiting the collisions of circulating proton and lead beams and, since 2015, is pioneering fixed-target physics at the LHC with the injection of helium, neon, and argon in the accelerator beam-pipe. A further extension of both programmes is now expected along with the experiment upgrade. In this document, the expected performance for data reconstruction and the related physics opportunities are discussed.

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In 2018 he ATLAS detector started the preparations for an ambitious physics project, aiming at the exploration of very rare processes and extreme phase spaces, an endeavor that will require a substantial increase in the amount of data to be taken. To accomplish this purpose, a comprehensive upgrade of the detector and associated systems was devised and planned to be carried out in two phases. The Phase-I upgrade program, completed in 2021, includes new features for the muon detector, for the electromagnetic calorimeter trigger system, and for all trigger and data acquisition chain. For the heavy-ion program, a new Zero Degree Calorimeter (ZDC) with improved radiation hardness will be installed. Upon reaching an integrated luminosity of 350 fb\(^{-1}\), the LHC will undergo a new upgrade, becoming the High-Luminosity LHC (HL-LHC).

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The CBM experiment at the Facility for Antiproton and Ion Research (FAIR) aims to explore the QCD phase diagram in the region of high net-baryon densities using nucleus–nucleus collisions (\(\sqrt {s_{NN}} = 2.9\)–4.9 GeV). The CBM will be utilizing peak interaction rates of up to 10 MHz and an advanced triggerless data acquisition scheme to provide it with a unique access to rare physics probes required to accomplish CBM’s physics goals. This contribution will summarise CBM’s progress in terms of its physics performance simulations and the status of the comprising detector sub-systems, including their involvement in FAIR Phase-0 activities.

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The J-PARC E16 experiment focuses on a measurement of the spectral modification of vector mesons at nuclear density. In the experiment, 30-GeV primary proton beam is irradiated on targets to produce vector mesons, \(\rho \), \(\omega \), and \(\phi \). The medium mass modifications of the vector mesons are investigated using their decay into \(e^+e^-\). The experiment has been successfully launched at J-PARC high momentum beamline in 2020, and three commissioning runs have been carried out in 2020–2021. The first physics run is planned in 2023. In this article, preliminary results of the commissioning runs are presented.

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The high-\(\mu _{B}\) region of the QCD phase diagram has become the object of several studies, focused on the investigation of the order of the phase transition and the search for the critical point. Accessing rare probes is experimentally challenging as it requires large integrated luminosities, and a fixed-target environment represents an ideal solution for these studies. The CERN SPS covers, with large beam intensity, the collision energy region of \(5\lt \sqrt {s_{NN}}\lt 17\) GeV. A future experiment, NA\(60+\), is being proposed to access this region and perform accurate measurements of the dimuon spectrum from threshold up to the charmonium mass region, and of hadronic decays of charm and strange hadrons. The experiment, which is also part of the Physics Beyond Colliders CERN initiative, aims at taking its first data with Pb and proton beams around 2029.

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ALICE pursues several upgrades to further extend its physics reach. For Run 4, ALICE is pioneering the construction of truly cylindrical tracking layers, which will improve the measurements of heavy-flavour hadrons and dielectrons. In addition, a Forward Calorimeter (FoCal) for the measurement of direct photons is being developed to access the gluon distributions of nucleons and nuclei at low \(x\). For Run 5 and beyond, ALICE 3 is proposed. It combines a unique high-resolution vertex detector with a silicon pixel tracker and modern particle identification solutions over a large acceptance. This will permit heavy-flavour and dielectron measurements with unprecedented precision to access fundamental properties and dynamics of the quark–gluon plasma (QGP). We will discuss the upgrade plans, report on R&D results for ITS3 and FoCal, and present the requirements and concepts for ALICE 3.

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In March 2019, the HADES experiment recorded 14 billion Ag\(+\)Ag collisions at \(\sqrt {s_{NN}}=2.55\) GeV as a part of the FAIR phase-0 physics program. In this contribution, we discuss the reconstruction and analysis of weakly decaying strange hadrons and hypernuclei emerging from these collisions. Focus is put on measuring the mean lifetimes of these particles.

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The mechanisms leading to the production of light- and intermediate-mass nuclei and hypernuclei in reactions initiated by relativistic nuclei are under study with dynamical and statistical models. We prove a novel mechanism responsible for combining nucleons and hyperons into complex nuclei in central collisions: The intermediate excited clusters of baryons can stochastically be formed at a low sub-nuclear density after the dynamical expansion of the nuclear matter. One can describe the nucleation process within the statistical approach as the disintegration of such clusters. This approach is able to describe the experimental data measured in central collisions that was not possible with other methods. The important consequence of this novel mechanism is the correlations of the produced nuclear species.

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In these proceedings, we present the measurements of centrality, transverse momentum, and rapidity dependences of proton (\(p\)) and light-nuclei (\(d\) (\(\bar {d}\) ), \(t\), \(^{3}\mathrm {He}\) (\(\overline {^{3}\mathrm {He}}\)), and \(^{4}\mathrm {He}\)) production in Au\(+\)Au collisions at \(\sqrt {s_{NN}} = 3\) GeV, and isobaric (Ru\(+\)Ru and Zr\(+\)Zr) collisions at \(\sqrt {s_{NN}} = 200\) GeV. The compound yield ratios in central collisions at 3 GeV are found to be larger than the transport model calculations. Furthermore, the kinetic freeze-out parameters at 3 GeV show a different trend compared to those of light hadrons (\(\pi \), \(K\), \(p\)) at higher energies.

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The hypertriton (\(^{3}_{\mit \Lambda }\mathrm {H}\)) is a bound state of a proton, a neutron, and a \({\mit \Lambda }\) baryon. Studying its internal structure is crucial to investigate the hyperon–nucleon (\(Y\)–\(N\)) strong interaction and offers insights into the inner core of neutron stars, where \({\mit \Lambda }\) production is favoured. Measuring precisely the \(^{3}_{\mit \Lambda }\mathrm {H}\) lifetime, \(\tau _{^{3}_{\mit \Lambda }\mathrm {H}}\), and \({\mit \Lambda }\) separation energy, \(B_{\mit \Lambda }\), provide a powerful tool for constraining the parameters of the \(Y\)–\(N\) potential, as \(\tau _{^{3}_{\mit \Lambda }\mathrm {H}}\) and \(B_{\mit \Lambda }\) directly reflect the strength of the \(Y\)–\(N\) interaction. The most precise measurements to date of \(\tau _{^{3}_{\Lambda }\mathrm {H}}\) and \(B_{\mit \Lambda }\) are obtained by the ALICE Collaboration, using the data sample of Pb–Pb collisions at a centre-of-mass energy per nucleon pair of \(\sqrt {s_{NN}}= 5.02\) TeV. These measurements strongly support the loosely-bound nature of \(^{3}_{\mit \Lambda }\mathrm {H}\) and shed light on the \(Y\)–\(N\) interaction. Furthermore, the weakly bound nature of the \(^{3}_{\mit \Lambda }\mathrm {H}\) has important implications on our understanding of the nucleosynthesis mechanism in hadronic collisions. Indeed, the large size of the \(^{3}_{\mit \Lambda }\mathrm {H}\) wave function determines a large separation between the nuclei production models at low charged-particle multiplicity. For this reason, the first measurement of the production of \(^{3}_{\mit \Lambda }\mathrm {H}\) in \(p\)–Pb collisions at \(\sqrt {s_{NN}} = 5.02\) TeV performed by ALICE represents an ideal probe for discriminating between the nuclei production mechanisms in high-energy hadron–hadron collisions.

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Hypernuclei are expected to be abundantly produced in the intermediate-to-low energy heavy-ion collisions due to the high baryon density. Measurements of the yield and collective flow are sensitive to their production mechanisms and the dynamics of the produced medium. In particular, hypernuclei measurements may also bear implications on the hyperon–nucleon interaction, which is critical for understanding the nuclear equation of state in high baryon density medium including strangeness degrees of freedom. The STAR Beam Energy Scan Phase II program, carried out during 2018–2021, is particularly suited for such studies. In this paper, the collision energy dependence of light hypernuclei (\({}^{3}_{\mit \Lambda }\)H, \({}^{4}_{\mit \Lambda }\)H, \({}^{4}_{\mit \Lambda }\)He) production yields in \(\sqrt {s_{NN}}=3.0\), 19.6, and 27.0 GeV Au\(+\)Au collisions will be presented. Results on hypernuclei-directed flow will also be presented. Furthermore, measurements of hypernuclei lifetimes and relative branching ratios will be reported. The physics implications of our measurements in the context of hypernuclear structure and their production mechanisms will be discussed.

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We present a demonstration of the design sampling and closure for the first comprehensive Bayesian model-to-data comparison of heavy-ion measurements with IP-Glasma initial conditions, in which we combine with state-of-the-art hydrodynamics (MUSIC), particlization (iS3D), and transport (SMASH). We further introduce a systematically-improvable method of sampling design points with better projection properties to explore the parameter space of the model for the first time in heavy-ion collisions.

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Photonuclear collisions are one of the simplest processes possible in a heavy-ion collision. They occur when one nucleus emits a quasi-real photon which interacts with the another colliding nucleus, similar to an \(e+A\) collision except that the photon tends to have much smaller virtuality. Results are presented for identified \(\pi ^\pm \), \(K^\pm \), and \(p(\bar {p})\) spectra in photonuclear collisions at STAR for Au+Au collisions at \(\sqrt {s_{_{NN}}} = 54.4\) GeV. Significant baryon stopping and rapidity asymmetry are observed at low transverse momentum, which could indicate the existence of a baryon junction within the nucleon, a nonperturbative Y-shaped configuration of gluons which carries the baryon number and is attached to all three valence quarks. Measurements of identified particle spectra and their rapidity dependence in \(\gamma +A\) events will give insights into the origin of baryon stopping and also inform future measurements of identified particles at the Electron-Ion Collider.

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The quark model has proven successful in describing the basic building blocks of strongly interacting particles in the Standard Model, where hadronic states consist of quarks and gluons. At the same time, Lattice QCD predicts the possibility of glueball candidates in the mass range of 1550–1750 MeV/\(c^2\), which have never been observed. The experimental search for the existence of mesons with no quark content is both interesting and challenging as the glueball is very likely to mix with surrounding quark–antiquark scalar meson states with the same quantum numbers. The large statistics data sample collected by ALICE in \(pp\) collisions at the highest LHC center-of-mass energy provides an opportunity to measure high mass resonances, whose characteristics and internal structure are still unknown. In this article, we report on the measurements of invariant mass distributions of higher mass resonances using the decay channels of \(K^{0}_\mathrm {S}{K}^{0}_\mathrm {S}\) and \(K^{+}K^{-}\) pairs in \(pp\) collisions at \(\sqrt {s} = 13\) TeV using the ALICE detector at midrapidity.

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Jets are collimated sprays of hadrons and can serve as an experimental tool for studying the dynamics of quarks and gluons. The SoftDrop grooming technique utilizes the angular ordered Cambridge/Aachen reclustering tree and provides a correspondence between the experimental observables such as the shared momentum fraction (\(z_{\rm {g}}\)), groomed jet radius, or split opening angle (\(R_{\rm {g}}\)), and the QCD splitting functions in vacuum. We present fully corrected correlations between \(z_{\rm {g}}\) and \(R_{\rm {g}}\) at the first split of jets at varying momenta and radii in \(pp\) collisions at \(\sqrt {s} = 200\) GeV. To study the evolution along the jet shower, we also present the splitting observables at the first, second, and third splits along the jet shower for various jet momenta.

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We construct a framework to describe the dynamics of the critical fluctuations in high-energy nuclear collisions. We consider the relaxation time \(\tau _{\mathrm {R}}\) for the baryon diffusion current and the coupling of the chiral condensate fluctuation \(\delta \sigma \) to the baryon density fluctuation \(\delta n\). We apply this framework to a one-dimensionally expanding system with the QCD critical point and investigate the effects of the relaxation time \(\tau _{\mathrm {R}}\) and the mode coupling on the correlation of baryon density fluctuations \(\delta n\) as a function of the rapidity interval. We show that the non-zero relaxation time makes the signal propagate at a finite speed, which results in a time lag in the response of correlation evolution of baryon number fluctuations \(\delta n\) from chiral fluctuations.

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We show that high-\(p_\perp \) \(R_{AA}\) and \(v_2\) are way more sensitive to the initial time of fluid-dynamical expansion \(\tau _0\) than the distributions of low-\(p_\perp \) particles, and that the high-\(p_\perp \) observables prefer relatively late \(\tau _0 \sim 1\) fm/\(c\). To calculate high-\(p_\perp \) \(R_{AA}\) and \(v_2\), we employ our DREENA-A framework, which combines state-of-the-art dynamical energy loss model with 3+1-dimensional hydrodynamical simulations. Elliptic flow parameter \(v_2\) is also more sensitive to \(\tau _0\) than \(R_{AA}\). This presents an example of applying QGP tomography to constrain a bulk QGP parameter with high-\(p_\perp \) observables and related theory.

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We investigate the effects of the pre-equilibrium Glasma stage of heavy-ion collisions on the broadening of momentum for heavy quarks and jets using classical colored particle simulations based on Wong’s equations. Confirming previous studies, we find that these probes accumulate momentum on the order of the saturation scale \(Q_{\mathrm {s}}\) and that the color field of the Glasma induces an anisotropy with more broadening along the beam axis. For quark jets, the anisotropy is more pronounced at lower energies.