Production In Relativistic Heavy Ion Collisions Research Articles

Exploring the higher-order QED effects on the differential distributions of vacuum pair production in relativistic heavy-ion collisions

Extensive studies have been conducted in the past few decades to investigate potential signatures of higher-order QED effects in high-energy electromagnetic scattering processes. In our previous work, we have identified evidence of higher-order corrections in the total cross-section for the vacuum pair production in relativistic heavy-ion collisions. However, the presence of higher-order QED corrections cannot be unambiguously proven solely based on total cross-section measurements due to substantial experimental and theoretical uncertainties. The objective of this paper is to explore the sensitivity of specific differential observables in the vacuum pair production to higher-order QED effects in high-energy heavy-ion collisions. These investigations will provide guidance in determining the presence or absence of higher-order QED processes by conducting precise measurements in future experiments.

Effect of nuclear structure on particle production in relativistic heavy-ion collisions using a multiphase transport model

Effect of nuclear structure on particle production in relativistic heavy-ion collisions using a multiphase transport model

Light-Nuclei Production in Heavy-Ion Collisions at sNN = 6.4 – 19.6 GeV in THESEUS Generator Based on Three-Fluid Dynamics

Light-nuclei production in relativistic heavy-ion collisions is simulated within an updated Three-fluid Hydrodynamics-based Event Simulator Extended by UrQMD (Ultra-relativistic Quantum Molecular Dynamics) final State interactions (THESEUS). The simulations are performed in the collision energy range of sNN= 6.4–19.6 GeV. The light-nuclei are produced within the thermodynamical approach on an equal basis with hadrons. Since the light nuclei do not participate in the UrQMD evolution, the only additional parameter related to the light nuclei, i.e., the energy density of late freeze-out, is used for the imitation of the afterburner stage of the collision. The updated THESEUS provides a reasonable reproduction of data on bulk observables of the light nuclei, especially their functional dependence on the collision energy and light-nucleus mass. Various ratios, d/p, t/p, t/d, and N(t)×N(p)/N2(d), are also considered. Imperfect reproduction of the light-nuclei data leaves room for medium effects in produced light nuclei.

Light-nuclei production in heavy-ion collisions within a thermodynamical approach

We present results of simulations of light-nuclei production in relativistic heavy-ion collisions within updated Three-fluid Hydrodynamics-based Event Simulator Extended by UrQMD (Ultra-relativistic Quantum Molecular Dynamics) final State interactions (THESEUS). The simulations were performed for Pb+Pb and Au+Au collisions in the collision energy range of $\sqrt{s_{NN}}=$ 6.4--19.6 GeV. The light-nuclei production is treated within the thermodynamical approach on equal basis with hadrons. The only additional parameter related to the light nuclei is the energy density of late freeze-out that imitates afterburner stage of the collision because the light nuclei do not participate in the UrQMD evolution. This parameter is fixed from the condition of the best reproduction of the proton transverse-momentum spectrum after the UrQMD afterburner by that at the late freeze-out. The updated THESEUS results in not perfect, but a reasonable reproduction of data on bulk observables of the light nuclei, especially their functional dependence on the collision energy and light-nucleus mass. Various ratios, $d/p$, $t/p$, $t/d$, and $N(t)\times N(p)/N^2(d)$, are also considered. The directed flow of light nuclei turns out to be more involved. Apparently, it requires explicit treatment of the afterburner evolution of light nuclei that violates the kinetic equilibrium. Imperfect reproduction of the light-nuclei data leaves room for medium effects in produced light nuclei.

Investigating color screening in proton-nucleus collisions with complex potentials* *Supported by the National Natural Science Foundation of China (NSFC) (12175165, 11705125); S.S. acknowledges support from U.S. Department of Energy, Office of Science, Office of Nuclear Physics, (DE-FG88ER40388); X.D acknowledges support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through the CRC-TR 211 'Strong-interaction matter under extreme conditions’– project number 315477589

Color screening and parton inelastic scattering modify the heavy-quark antiquark potential in mediums consisting of particles from quantum chromodynamics (QCD), leading to the suppression of quarkonium production in relativistic heavy-ion collisions. Owing to the small charm/anti-charm () pair production number in proton-nucleus (pA) collisions, the correlation between different pairs is negligible, which makes the Schrödinger equation viable for tracking the evolution of only one pair. We employ the time-dependent Schrödinger equation with an in-medium potential to study the evolution of charmonium wave functions in a hydrodynamic-like QCD medium produced in pA collisions. We explore different parametrizations of real and imaginary parts of the potential and calculate the nuclear modification factors () of and in TeV energy p-Pb collisions at the Large Hadron Collider (LHC). Comparing strong and weak screening scenarios with experimental data in this approach, we arrive at the conclusion that color screening is weak at temperatures close to the deconfined phase transition. Moreover, the imaginary part of the potential is crucial in describing the experimental data, which is consistent with widely studied semi-classical approaches, where dissociation rates are essential.

General balance functions of identified charged hadron pairs of (π,K,p) in Pb–Pb collisions at [formula omitted] 2.76 TeV

First measurements of balance functions (BFs) of all combinations of identified charged hadron (π,K,p) pairs in Pb–Pb collisions at sNN=2.76 TeV recorded by the ALICE detector are presented. The BF measurements are carried out as two-dimensional differential correlators versus the relative rapidity (Δy) and azimuthal angle (Δφ) of hadron pairs, and studied as a function of collision centrality. The Δφ dependence of BFs is expected to be sensitive to the light quark diffusivity in the quark–gluon plasma. While the BF azimuthal widths of all pairs substantially decrease from peripheral to central collisions, the longitudinal widths exhibit mixed behaviors: BFs of ππ and cross-species pairs narrow significantly in more central collisions, whereas those of KK and pp are found to be independent of collision centrality. This dichotomy is qualitatively consistent with the presence of strong radial flow effects and the existence of two stages of quark production in relativistic heavy-ion collisions. Finally, the first measurements of the collision centrality evolution of BF integrals are presented, with the observation that charge balancing fractions are nearly independent of collision centrality in Pb–Pb collisions. Overall, the results presented provide new and challenging constraints for theoretical models of hadron production and transport in relativistic heavy-ion collisions.

Energy and centrality dependence of light nuclei production in relativistic heavy-ion collisions

Energy and centrality dependence of light nuclei production in relativistic heavy-ion collisions

Effects of chiral symmetry restoration on meson and dilepton production in relativistic heavy-ion collisions

We include effects of chiral symmetry and its restoration in the kinetic equations for baryon propagation and explore the consequences for $\eta$, $\pi^0$, $\rho$ and dilepton production in heavy-ion collisions at 1-2A GeV. Numerical calculations are performed using the GiBUU microscopic transport model supplemented by the parity-doublet model for the mean fields of the nucleon and the $N^*(1535)$ resonance. In this chiral model, a strong dropping of the Dirac mass of the $N^*(1535)$ in the high-density stage of a collision leads to a considerable enhancement in the production of this resonance as compared to the standard (non-linear) Walecka model. As the system expands, the Dirac masses of these abundant soft $N^*(1535)$ resonances gradually increase and ultimately cross the $N \eta$ decay threshold. As a result, an enhanced low-energy $\eta$ production is observed in the calculations with chiral mean fields. Comparing with TAPS data on $\eta$ and $\pi^0$ production we find that the chiral model improves the agreement for the $m_t$-spectra of $\eta$'s at small $m_t$ in heavy colliding systems. A similar enhancement is also observed in the soft $\rho$ production due to chiral symmetry and its partial restoration. The resulting dilepton yields at low and intermediate invariant masses are slightly enhanced due to these chiral effects which further improve the agreement between GiBUU transport simulations and HADES data for C+C at 1A GeV.

Cluster and hypercluster production in relativistic heavy-ion collisions within the parton-hadron-quantum-molecular-dynamics approach

We study cluster and hypernuclei production in heavy-ion collisions at relativistic energies employing the Parton-Hadron-Quantum-Molecular-Dynamics (PHQMD) approach, a microscopic n-body transport model based on the QMD propagation of the baryonic degrees of freedom with density dependent 2-body potential interactions. All other ingredients of PHQMD, including the collision integral and the treatment of the quark-gluon plasma (QGP) phase, are adopted from the Parton-Hadron-String Dynamics (PHSD) approach. In PHQMD the cluster formation occurs dynamically, caused by the interactions. The clusters are recognized by the Minimum Spanning Tree (MST) algorithm. We present the PHQMD results for cluster and hypernuclei formation in comparison with the available experimental data at AGS, SPS, RHIC-BES and RHIC fixed target energies. We also provide predictions on cluster production for the upcoming FAIR and NICA experiments. PHQMD allows to study the time evolution of formed clusters and the origin of their production, which helps to understand how such weakly bound objects are formed and survive in the rather dense and hot environment created in heavy-ion collisions. It offers therefore an explanation of the 'ice in the fire' puzzle.

Multiplicity scaling of light nuclei production in relativistic heavy-ion collisions

Using the nucleon coalescence model based on kinetic freeze-out nucleons from the 3D MUSIC+UrQMD and the 2D VISHNU hybrid model with a crossover equation of state, we study the multiplicity dependence of deuteron (d) and triton (t) production from central to peripheral Au+Au collisions at sNN= 7.7, 14.5, 19.6, 27, 39, 62.4 and 200 GeV and Pb+Pb at sNN=2.76 TeV, respectively. It is found that the ratio NtNp/Nd2 of the proton yield Np, deuteron yield Nd and triton yield Nt exhibits a scaling behavior in its multiplicity dependence, i.e., decreasing monotonically with increasing charged-particle multiplicity. A similar multiplicity scaling of this ratio is also found in the nucleon coalescence calculation based on kinetic freeze-out nucleons from a multiphase transport (AMPT) model. The scaling behavior of NtNp/Nd2 can be naturally explained by the interplay between the sizes of light nuclei and the nucleon emission source. We further argue that the multiplicity scaling of NtNp/Nd2 can be used to validate the production mechanism of light nuclei, and the collision energy dependence of this yield ratio can further serve as a baseline in the search for the QCD critical point in relativistic heavy-ion collisions.

Double strangeness Ξ− production as a probe of nuclear equation of state at high densities

Double strangeness Ξ− production in Au+Au collisions at 2, 4, and 6 GeV/nucleon incident beam energies is studied with the pure hadron cascade version of a multi-phase transport model. It is found that due to larger nuclear compression, the model with the soft equation of state (EoS) gives larger yields of both single strangeness (K+ and Λ+Σ0) and double strangeness Ξ−. The sensitivity of the double strangeness Ξ− to the EoS is evidently larger than that of K+ or Λ+Σ0 since the phase-space distribution of produced Ξ− is more compact compared to those of the single strangeness. The larger sensitivity of the yields ratio of Ξ− to the EoS from heavy and light systems is kept compared to that of the single strangeness. The study of Ξ− production in relativistic heavy-ion collisions provides an alternative for the ongoing heavy-ion collision program at facilities worldwide for identifying the EoS at high densities, which is relevant to the investigation of the phase boundary and onset of deconfinement of dense nuclear matter.

Progress in experimental studies of the mechanism of strange hadron production in relativistic heavy-ion collisions

Progress in experimental studies of the mechanism of strange hadron production in relativistic heavy-ion collisions

Update of the three-fluid hydrodynamics-based event simulator: Light-nuclei production in heavy-ion collisions

We present an update of the event generator based on the three-fluid dynamics (3FD), complemented by Ultra-relativistic Quantum Molecular Dynamics (UrQMD) for the late stage of the nuclear collision~-- the three-fluid Hydrodynamics-based Event Simulator Extended by UrQMD final State interactions (THESEUS). Two modifications are introduced. The THESEUS table of hadronic resonances is made consistent with that of the underlying 3FD model. The main modification is that the generator is extended to simulate the light-nuclei production in relativistic heavy-ion collisions, on the equal basis with hadrons. These modifications are illustrated by applications to the description of available experimental data. The first run of the updated generator revealed a good reproduction of the NA49 data on the light nuclei. The reproduction is achieved without any extra parameters, while the coalescence approach in 3FD requires special tuning of the coalescence coefficients for each light nucleus separately.

Effects of QCD critical point on light nuclei production

Using the nucleon coalescence model, which can naturally take into account the correlations in the nucleon density distribution, we study the effects of QCD critical point on light nuclei production in relativistic heavy-ion collisions. We find that the yield ratio NtNp/Nd2 of proton (p), deuteron (d) and triton (t) increases monotonically with the nucleon density correlation length, which is expected to increase significantly near the critical point in the QCD phase diagram. Our study thus demonstrates that the yield ratio NtNp/Nd2 can be used as a sensitive probe of the QCD critical phenomenon. We further discuss the relation between the QCD phase transitions in heavy-ion collisions and the possible non-monotonic behavior of NtNp/Nd2 in its collision energy dependence.

Hadron Yields in Central Nucleus–Nucleus Collisions, the Statistical Hadronization Model and the QCD Phase Diagram

The description of hadron production in relativistic heavy-ion collisions in the statistical hadronization model is very good, over a broad range of collision energy. We outline this both for the light (u, d, s) and heavy (charm) quarks and discuss the connection it brings to the phase diagram of QCD.

Overview of light nuclei production in relativistic heavy-ion collisions

We briefly overview motivations, some recent results and challenges in studying light nuclei production in relativistic heavy ion collisions.

Charmed hadron chemistry in relativistic heavy-ion collisions

We develop for charmed hadron production in relativistic heavy-ion collisions a comprehensive coalescence model that includes an extensive set of s and p-wave hadronic states as well as the strict energy-momentum conservation, which ensures the boost invariance of the coalescence probability and the thermal limit of the produced hadron spectrum. By combining our hadronization scheme with an advanced Langevin-hydrodynamics model that incorporates both elastic and inelastic energy loss of heavy quarks inside the dynamical quark-gluon plasma, we obtain a successful description of the pT-integrated and differential Λc/D0 and Ds/D0 ratios measured at RHIC and the LHC. We find that including the effect of radial flow of the medium is essential for describing the enhanced Λc/D0 ratio observed in relativistic heavy-ion collisions. We also find that the puzzling larger Λc/D0 ratio observed in Au+Au collisions at RHIC than in Pb+Pb collisions at the LHC is due to the interplay between the effects of the QGP radial flow and the charm quark transverse momentum spectrum at hadronization. Our study further suggests that charmed hadrons have larger sizes in medium than in vacuum.

Anomalous features of particle production in high-multiplicity events of pp collisions at the LHC energies

Prevalent models of multiparticle production in relativistic $pp$ collisions at pre-LHC energies fail to provide convincing explanations of certain significant features of the final-state charged particles in high-multiplicity $pp$ events at the LHC. In this article we study these features---which are usually interpreted as the collective behavior of particle production in relativistic heavy-ion collisions---in the framework of the hydrodynamic epos3 model, emphasizing a quantitative comparison between the data and model-based simulations in the same kinematic ranges for better understanding of the data. The work reveals a quantitative mismatch between the data and the model.

Phenomenological models of two-particle correlation distributions on transverse momentum in relativistic heavy-ion collisions

Two-particle, pair-number correlation distributions on two-dimensional transverse momentum ($p_{t1},p_{t2}$) constructed from the particle production in relativistic heavy-ion collisions allow access to dynamical processes in these systems beyond what can be studied with angular correlations alone. Only a few measurements of this type have been reported in the literature and phenomenological models, which facilitate physical interpretation of the correlation structures, are non-existent. On-going effort at the Relativistic Heavy-Ion Collider (RHIC) will provide a significant volume of these correlation measurements in the future. In anticipation of these new data two phenomenological models are developed which describe two-dimensional 2D correlation distributions on transverse momentum. One model is based on a collision event-by-event fluctuating blast wave. The other is based on event-by-event fluctuations in fragmenting color-flux tubes and in jets. Both models are shown to be capable of accurately describing the measured single-particle $p_t$ distributions for minimum-bias Au+Au collisions at $\sqrt{s_{\rm NN}} = 200$~GeV. Both models are then applied to preliminary, charged-particle correlation measurements on 2D transverse momentum. The capabilities of the two models for describing the overall structure of these correlations, the stability of the fitting results with respect to collision centrality, and the resulting trends of the dynamical fluctuations are evaluated. In general, both phenomenological models are capable of qualitatively describing the major correlation structures on transverse momentum and can be used to establish the required magnitudes and centrality trends of the fluctuations. Both models will be useful for interpreting the forthcoming correlation data from the RHIC.

Energy dependence of light (anti)nuclei and (anti)hypertriton production in the Au-Au collision from $\sqrt{s_{NN}} = 11.5$ s N N = 11 . 5 to 5020 GeV

The energy dependence of light (anti)nuclei and (anti)hypertriton production are investigated in central Au-Au collisions from AGS up to LHC energies at midrapidity, using the parton and hadron cascade model (PACIAE) together with the dynamically constrained phase-space coalescence model(DCPC). We find that the yields, yield ratios of the antiparticles to their corresponding particles, the coalescence parameters $B_A$ and the strangeness population factor $s_3$ of light (anti)nuclei and (anti)hypertriton strongly depend on the energy. Furthermore, we analyze and discuss the strangeness population factor $s_3$ and the coalescence parameters $B_A$, and find a transition point near by 20 GeV. These results thus suggest the potential usefulness of the $s_3$ and $B_A$ of light nuclei production in relativistic heavy-ion collisions as a direct probe of the transition point associated with the QCD critical phenomena. The results from PACIAE+DCPC model are well consistent with experimental data.