Search Results (265)

Jet quenching provides a valuable measure of the opacity of the quark–gluon plasma (QGP) produced in high-energy heavy-ion collisions. However, substantial suppression of charged hadron spectra is observed in highly peripheral collisions, despite the expectation of negligible jet–QGP interactions in this regime. To address this, we develop a HIJING-based initial condition model that accounts for the impact parameter dependence of both inelastic nucleon–nucleon (NN) collisions and the number of hard partonic scatterings per inelastic NN collision. This dependence introduces a geometric bias effect on the jet yield within a given centrality class of nucleus–nucleus (AA) collisions, suppressing the high-$p_{\mathrm{T}}$ hadron spectrum in peripheral collisions due to dilute nucleon overlap at large AA impact parameters. By combining this improved initial condition model with a linear Boltzmann transport model for jet–QGP interactions, we obtain a satisfactory description of the centrality dependence of charged hadron suppression in Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV. Full article

We investigate finite-size effects in the T–$\mu$ phase diagram of magnetized quark matter within the framework of a nonlocal extension of the Polyakov–Nambu–Jona-Lasinio (PNJL) model. Finite-size corrections are incorporated through the multiple reflection expansion (MRE) formalism, which describes a spherical quark droplet of radius R and modifies the density of states by including surface and curvature contributions. We consider two-flavor quark matter at finite temperature and chemical potential in the presence of a uniform magnetic field with strengths ranging from $eB=0$ to 1 ${\mathrm{GeV}}^2$, and droplet radii from $R=3$ fm to the bulk limit. The nonlocal PNJL (nlPNJL) model naturally reproduces both magnetic catalysis at low temperatures and inverse magnetic catalysis near the chiral transition, in agreement with lattice QCD results. We analyze the chiral condensate, the traced Polyakov loop, the normalized quark condensate, and the corresponding susceptibilities. We find that finite-size effects do not modify the overall structure of the phase diagram, and that the coincidence of the chiral restoration and deconfinement transitions persists for all magnetic field strengths and system sizes explored, within the present implementation in which finite-size corrections are restricted to the fermionic sector. However, the critical end point (CEP) is notably shifted as a function of both magnetic field strength and system size: It moves toward higher chemical potentials and lower temperatures as system size decreases, an effect that is significantly amplified by strong magnetic fields. Our results have potential implications for the physics of phase conversion in compact stars and for the interpretation of relativistic heavy-ion collision experiments. Full article

The spin alignment of vector mesons, characterized by the spin-density-matrix element ${\rho }_{00}$, is an important observable for studying spin dynamics in relativistic heavy-ion collisions. Experimental measurements have reported deviations of ${\rho }_{00}$ from the isotropic expectation of $1/3$, motivating careful evaluation of possible acceptance effects. In this work, we investigate the influence of finite experimental coverage on the extracted ${\rho }_{00}$ of $K^{\ast 0}$ mesons using a toy model constrained by realistic kinematic distributions from the AMPT model. The reconstructed ${\rho }_{00}$ is examined as a function of pseudorapidity ($\eta$) and transverse momentum ($p_T$) within typical experimental acceptance ranges. We find that limited pseudorapidity coverage can lead to reconstructed ${\rho }_{00}$ values above $1/3$, even when the input distribution is isotropic. This behavior originates from the selective removal of decay daughters outside the $\eta$ window, which modifies the $cos{\theta }^{\ast }$ distribution. A dependence on transverse momentum is also observed, particularly at low $p_T$ where daughter particles are more sensitive to longitudinal acceptance constraints. Comparisons with STAR measurements are presented for reference, without attempting to reinterpret the experimental results. Overall, this study provides a systematic examination of acceptance-induced effects and may serve as a useful reference for future measurements of vector-meson spin alignment. Full article

We present a study of the mean transverse momentum $⟨p_{\mathrm{T}}⟩$ of identified strange hadrons (${\mathrm{K}}_{\mathrm{S}}^0,\Lambda ,\overline{\Lambda },{\Xi }^{-},{\overline{\Xi }}^{+},\varphi ,{\Omega }^{-},{\overline{\Omega }}^{+}$) produced in Au+Au collisions at RHIC-BES energies (the nucleon–nucleon center-of-mass energy $\sqrt{s_{\mathrm{N}\mathrm{N}}}=7.7 \mathrm{G}\mathrm{e}\mathrm{V},11.5 \mathrm{G}\mathrm{e}\mathrm{V},19.6 \mathrm{G}\mathrm{e}\mathrm{V},27 \mathrm{G}\mathrm{e}\mathrm{V}$ and $39 \mathrm{G}\mathrm{e}\mathrm{V}$). The mean transverse momentum is obtained from transverse momentum spectra of the strange hadrons as measured by the STAR experiment and its dependence on the number of participants $N_{\mathrm{p}\mathrm{a}\mathrm{r}\mathrm{t}}$ is studied. For RHIC-BES energies, experimental data indicate a centrality dependence of $⟨p_{\mathrm{T}}⟩$, with an increase towards central collisions. This dependency is described using a power-law function to fit the data. The power-law exponent $\alpha$ is used to characterize the degree of flattening of $⟨p_{\mathrm{T}}⟩$ with respect to $N_{\mathrm{p}\mathrm{a}\mathrm{r}\mathrm{t}}$ and its dependency on the collision energy and particle mass is studied. Special emphasis is placed on $\varphi$-meson that has a smaller interaction cross-section, thus reflecting the properties of the early stages of the system’s evolution. The $⟨p_{\mathrm{T}}⟩$ of $\varphi$-mesons produced in Au+Au collisions at RHIC-BES energies are compared with the results obtained in Au+Au collisions at higher RHIC energies and in Pb+Pb collisions at SPS and LHC energies. A distinct energy dependence of $\varphi ⟨p_{\mathrm{T}}⟩$ values is identified. Furthermore, data indicate, when comparing peripheral and central heavy-ion collisions, that $\varphi$-meson $⟨p_{\mathrm{T}}⟩$ increases with system size, following two distinct trends. The results are compared with the predictions of the default and string-melting versions of the AMPT generator. We observe that the string-melting AMPT version describes the strange meson $⟨p_{\mathrm{T}}⟩$, but underpredicts the strange baryon $⟨p_{\mathrm{T}}⟩$ centrality dependence. The default AMPT overpredicts the ${\mathrm{K}}_{\mathrm{S}}^0$ and $\varphi$ meson $⟨p_{\mathrm{T}}⟩$ centrality dependence, while the strange baryon data are in general better described by this version of the model. The exponent $\alpha$ obtained from AMPT-simulated results does not describe the measurements satisfactorily. Full article

As a foundation for numerical solvers in computational electromagnetics, particularly for multiphysics and electromagnetic compatibility applications, Jefimenko’s equations offer a generalized solution to Maxwell’s equations, enabling the direct computation of electromagnetic fields from time-dependent source distributions without the boundary-condition artifacts inherent to grid-based methods. However, the numerical integration of these equations is computationally intensive, typically scaling as $\mathcal{O}\left(N_{\mathrm{s}}{N}_{\mathrm{o}}\right)$ for $N_{\mathrm{s}}$ source points and $N_{\mathrm{o}}$ observation points. In this paper, we present JefiFast, a highly optimized graphics processing unit (GPU) implementation that significantly outperforms the state-of-the-art JefiGPU algorithm. We identify that previous implementations are strictly memory-bound due to inefficient global memory transactions and a lack of data reuse. JefiFast addresses these bottlenecks through four key optimizations: (i) a packed memory layout (PML) using an array-of-structures approach to ensure coalesced memory access for source densities and their derivatives; (ii) geometry-aware shared memory tiling strategies that maximize L2 (level-2) cache hit rates and on-chip data reuse; (iii) pre-computation of time derivatives to minimize redundant arithmetic operations; and (iv) a robust observation domain decomposition strategy that enables linear scaling across multiple GPUs. Benchmarks demonstrate that JefiFast achieves speedups ranging from $4.08$ times (for ${30}^3$ grids on a single NVIDIA V100 graphic processor) to $84.51$ times (for ${50}^3$ grids on 4 NVIDIA V100 processors) compared to the baseline. Notably, for a ${50}^3$ grid on a single GPU, JefiFast reduces execution time from about 51 min to just about 2.6 min ($19.54$ times speedup). These performance advances make high-resolution relativistic heavy-ion collision simulations feasible in near real-time. Full article

Matter–antimatter asymmetry is a fundamental question in both astronomy and particle physics. Investigating antimatter is of great interest for testing the potential explanations of matter–antimatter asymmetry in our Universe. In relativistic heavy-ion collisions, the extremely high energy density and temperature are similar to the early Universe shortly after the Big Bang. In this paper, we review the recent progress in antimatter search and study heavy-ion collisions, with a focus on the RHIC-STAR and LHC-ALICE experiments, particularly the newly observed antimatter hypernuclei ${}_{\overline{\Lambda }}{}^4\overline{\mathrm{H}}$ and ${}_{\overline{\Lambda }}{}^4\overline{\mathrm{He}}$. The statistical thermal model and the coalescence production model can quantitatively describe the production yields and yield ratios, and the yield measurements of ${}_{\overline{\Lambda }}{}^4\overline{\mathrm{H}}$, ${}_{\overline{\Lambda }}{}^4\overline{\mathrm{He}}$ and their matter counterparts indicate the existence of spin-excited states of these (anti)hypernuclei. Furthermore, new measurements of the lifetimes of ${}_{\overline{\Lambda }}{}^3\overline{\mathrm{H}}$, ${}_{\overline{\Lambda }}{}^4\overline{\mathrm{H}}$ and their matter counterparts reveal no difference between a particle and its corresponding antiparticle, which validates the CPT theorem. Full article

Relativistic heavy-ion collisions generate ultra-strong magnetic fields that interact with the quark–gluon plasma (QGP), a key focus of high-energy physics research. This study investigates QGP energy density evolution under time-dependent magnetic fields within a (1 + 1)D relativistic magnetohydrodynamic (RMHD) framework integrated with Bjorken flow. Three magnetic field temporal evolution models (Type-1, Type-2, Type-3) are analyzed for two different equations of state: (1) $p={c_s}^{2}e$ (simplified ultra-relativistic), and (2) $p={c_s}^{2}e-2MB$ (magnetized conformal), incorporating a temperature-dependent magnetic susceptibility derived from lattice QCD. Results show that stronger magnetic fields consistently suppress QGP energy density decay, with suppression magnitude dependent on the magnetic field’s temporal profile. Ultra-relativistic fluids exhibit slowed energy decay due to magnetic pressure counteracting hydrodynamic expansion. In contrast, magnetized conformal fluids display faster energy dissipation under identical conditions, arising from the synergistic effect of enhanced magnetic fluid coupling, increased energy dissipation during interaction, and QGP’s perfect fluid expansion at elevated temperatures. Temperature-dependent magnetic susceptibility reveals a transition from diamagnetic (confined phase) to paramagnetic (deconfined QGP phase) behavior, introducing a feedback mechanism that strengthens energy retention at higher temperatures. This work clarifies the interplay between magnetic field dynamics, QCD phase structure, and hydrodynamic expansion, providing key observational signatures for distinguishing fluid types in heavy-ion collisions and advancing realistic modeling of magnetized QGP. Full article

We study the production of charged particles in ultrarelativistic collisions by using the string fragmentation model. To do this, we describe the $p_{\mathrm{T}}$ spectrum as the convolution of the Schwinger mechanism with string tension fluctuations that account for the stochastic nature of QCD. We found that heavy-tailed distributions are required to adequately reproduce the power-law tail of the $p_{\mathrm{T}}$ spectrum experimentally observed. Additionally, the heavy-tailed characteristic is also necessary for the KNO scale invariance of intense color interactions modeling hard processes in this framework. In this way, the initial state admits a nonextensive picture, leading to a final state out of equilibrium, in which particle production occurs in small regions at different temperatures. Applying this framework to ALICE data, we observe trends in the power-law exponent as a function of event multiplicity and collision centrality. These trends are consistent with enhanced hard-particle production in small systems and with high-$p_{\mathrm{T}}$-particle suppression in heavy-ion collisions. Full article

Symmetry is a key principle in physics that links basic invariances to the structure of matter and the evolution of the universe. In this review, we use symmetry as a unifying thread connecting nuclear structure, nuclear reactions, and dense matter, and we highlight how symmetry-based arguments connect laboratory observables to astrophysical constraints. We present the essential concepts in a form accessible to a broad physics audience. Full article

This review presents a unified account of the NA35, NA49, and NA61/SHINE experiments, which together form a continuous programme of heavy-ion studies conducted at the H2 beamline of the CERN North Area using the SPS accelerator. The programme, spanning about 40 years, was driven by the search for a high-density state of strongly interacting matter—the quark–gluon plasma (QGP)—and the transitions leading to it. The review focuses on this primary line of research. The highlights of the programme include the observation of the first signal of QGP creation at the top SPS energy in S+S collisions by NA35, evidence for the onset of deconfinement at low SPS energies by NA49, and the establishment by NA61/SHINE of the diagram of high-energy nuclear collisions, featuring transitions between hadron-, string-, and QGP-dominated regimes. This predominantly scientific review is complemented by brief personal recollections related to the discussed topics. Full article

In this study, we investigate temperature fluctuations in hot QCD matter using a three-flavor Polyakov loop-extended Nambu–Jona-Lasinio (PNJL) model. The high-order cumulant ratios $R_{n2}$ ($n>2$) exhibit non-monotonic variations across the chiral phase transition, characterized by slight fluctuations in the chiral crossover region and significant oscillations around the critical point. In contrast, distinct peak and dip structures are observed in the cumulant ratios at low-baryon chemical potential. These structures gradually weaken and eventually vanish at high chemical potential as they compete with the sharpening of the chiral phase transition, particularly near the critical point and the first-order phase transition. Our results indicate that these non-monotonic peak and dip structures in high-order cumulant ratios are associated with the deconfinement phase transition. This study quantitatively analyzes temperature fluctuation behavior across different phase transition regions, and the findings are expected to be observed and validated in heavy-ion collision experiments through measurements of event-by-event mean transverse momentum fluctuations. Full article

Large density fluctuations near the QCD critical point can be probed via intermittency analysis, which involves measuring scaled factorial moments (SFMs) of multiplicity distributions in relativistic heavy-ion collisions. Intermittency reflects the emergence of scale invariance and self-similar structures, which are closely related to symmetry principles and their breaking near a second-order phase transition. We present a systematic model study of intermittency for charged hadrons in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 7.7, 11.5, 19.6, 27, 39, 62.4, and 200 $\mathrm{GeV}$. Using the cascade UrQMD model, we demonstrate that non-critical background effects can produce sizable SFMs and a large scaling exponent if they are not properly removed using the mixed-event subtraction method. To estimate the possible critical intermittency signal in experimental data, we employ a hybrid UrQMD+CMC model, in which fractal critical fluctuations are embedded into the UrQMD background. A direct comparison of the second-order SFM between the model and STAR experimental data suggests that a critical intermittency signal on the order of approximately $1.8\%$ could be present in the most central Au+Au collisions at RHIC energies. This study provides practical guidance for evaluating background contributions in intermittency measurements and offers a quantitative estimate for the critical signal fraction present in the STAR data. Full article

(1) Purpose: Incoherent processes in production of lepton pairs (dileptons) are studied for the scattering of protons on nuclei. Methods: New quantum mechanical model is constructed on the basis (1) generalization of the nuclear model of emission of photons in the proton-nucleus reactions from low to intermediate energies, (2) formalism of dilepton production. Results: (1) The coherent cross sections of dilepton production in $p+\mathrm{Be}$ at proton beam energy $E_{\mathrm{p}}$ of 2.1 GeV calculated by model are in good agreement with experimental data of DLS Collaboration. (2) Dilepton production for ⁹Be, ¹²C, ¹⁶O, ²⁴Mg, ⁴⁴Ca, ¹⁹⁷Au at $E_{\mathrm{p}}=2.1$ GeV are studied. Coherent cross sections of dilepton production are monotonously decreased with increasing mass of nuclei. (3) At larger $E_{\mathrm{p}}$ dileptons are produced more intensively. (4) Incoherent processes in production of dileptons are studied for p + ⁹Be at E_p = 2.1 GeV. Agreement between experimental data and calculated cross sections is better, in to include incoherent processes to the model. A new phenomenon of suppression of production of dileptons at low energies due to incoherent processes is observed. This is explained by dominant coherent contribution at very low energies. (5) Longitudinal amplitude of virtual photon suppresses the cross section of dilepton production a little (effect is observed for p + ⁹Be at E_p = 2.1 GeV). (6) The contribution from incoherent processes plays a leading role in the dilepton production ((the ratio between the incoherent and coherent terms is 10–100). Also our model provides the tendencies of the full spectrum for p + ⁹³Nb at E_p = 3.5 GeV in good agreement with experimental data obtained by HADES collaboration, and shows large role of incoherent processes. Conclusions: Incoherent processes are much more important than coherent ones in study of dilepton production in this reaction. Full article

We study heavy-ion collisions with a focus on pion production using an extended parity doublet model implemented in the “DaeJeon Boltzmann–Uehling–Uhlenbeck” (DJBUU) code. We consider three different systems—¹⁰⁸Sn + ¹¹²Sn, ¹¹²Sn + ¹²⁴Sn, and ¹³²Sn + ¹²⁴Sn—at a beam energy of $E_{\mathrm{beam}}=270$ A MeV, with an impact parameter of 3 fm, and compare our results with the SπRIT data. Since one of the key features of the parity doublet model is the existence of a chiral-invariant mass $m_0$ that contributes to the nucleon mass, we investigate how pion production depends on the chiral-invariant mass in these heavy-ion collisions. We adopt the values of the chiral-invariant mass of 600, 700, and 800 MeV and find that the case with $m_0=800$ MeV best reproduces the experimental data. We also observe that a larger $m_0$ results in a higher maximum baryon density of nuclear matter produced during heavy-ion collisions. Full article

We study the thermodynamic properties produced in symmetric p–p collisions at $\sqrt{s_{NN}}=0.9\mathrm{TeV}$ and $7\mathrm{TeV}$, based on experimental data by the ALICE collaboration at CERN. Particularly, we analyze the initial temperature $T_i$, effective temperature T, freeze-out temperature $T_0$, chemical potential $\mu$, mean transverse momentum $⟨p_T⟩$, freeze-out volume V, and transverse flow velocity ${\beta }_T$ of different hadrons such as $K_S^0$, $\Lambda$, ${\Xi }^{-}$, and $d/\overline{d}$. To effectively use the transverse momentum $p_T$ distributions of these hadrons, and to extract the thermodynamic parameters, the Single-Slope Standard Distribution with and without the chemical potential $\mu$, the Double-Slope Standard Distribution, and the modified Standard Distribution Functions are applied separately to fit the experimental data. The Modified Standard Distribution Function provides the most accurate description of the ALICE experimental data as compared to the Single-Slope (with and without $\mu$) and Double-Slope Standard Distribution Function. We have investigated the correlation between the extracted thermodynamic parameters and the measurements of mass and energy of particles of the collision, and we observed that the increase in $\sqrt{s_{NN}}$ is positively correlated with $T_i$, T, $T_0$, $⟨p_T⟩$, V, and negatively correlated with $\mu$. The comparison of p–p collisions with heavy-ion collisions (Au–Au collisions) suggests the possibility of collective-like dynamics even in small systems, which supports the hypothesis of thermalization and partial de-confinement in high-energy p–p collisions, indicating a transition towards a quark-gluon plasma (QGP)-like medium. Full article