作者机构：
[Zhang, Liang; Liu, Feng] Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Hubei, Peoples R China.;[Zhang, Liang; Liu, Feng] Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Hubei, Peoples R China.;[Li, Cheng; Jiang, Kun] Univ Sci & Technol China, Dept Modern Phys, Hefei 230026, Anhui, Peoples R China.;[Zhang, Liang; Wang, Fuqiang; Jiang, Kun] Purdue Univ, Dept Phys & Astron, W Lafayette, IN 47907 USA.;[Wang, Fuqiang] Huzhou Univ, Sch Sci, Huzhou 313000, Zhejiang, Peoples R China.
通讯机构：
[Liu, Feng] C;Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Hubei, Peoples R China.;Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Hubei, Peoples R China.
摘要：
Background: Measurements of two-particle azimuthal angle correlations are a useful tool to study the distribution of jet energy loss; however, they are complicated because of the significant anisotropic flow background.
作者机构：
[Zhang, Chao; Zheng, Liang; Liu, Feng; Shi, Shusu; Lin, Zi-Wei] Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Hubei, Peoples R China;[Zhang, Chao; Zheng, Liang; Liu, Feng; Shi, Shusu; Lin, Zi-Wei] Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Hubei, Peoples R China;[Zheng, Liang] China Univ Geosci, Wuhan 430074, Hubei, Peoples R China;[Lin, Zi-Wei] East Carolina Univ, Dept Phys, Greenville, NC 27858 USA
通讯机构：
[Shi, Shusu] C;Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Hubei, Peoples R China. Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Hubei, Peoples R China.
摘要：
A multiphase transport (AMPT) model has been successful in explaining a wide range of observables in relativistic heavy ion collisions. In this work, we implement a newer set of free proton parton distribution functions and an impact parameter-dependent nuclear shadowing in the AMPT model. After refitting the parameters of the two-component initial condition model to the experimental data on pp and pp¯ total and inelastic cross sections from s∼ 4 GeV to 13 TeV, we study particle productions in pp and AA collisions. We show that the updated AMPT model with string melting can reasonably describe the overall particle yields and transverse momentum spectra for both pp and AA collisions at RHIC and LHC energies after we introduce a nuclear scaling of the minijet transverse momentum cutoff for AA collisions at LHC energies that is motivated by the color glass condensate. Since heavy flavor and high−pT particles are produced by perturbative-QCD processes and thus directly depend on parton distribution functions of nuclei, the updated AMPT model is expected to provide a more reliable description of these observables.
作者机构：
[Luo, Xiaofeng; Liu, Feng; Chen, Jiamin] Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Hubei, Peoples R China.;[Luo, Xiaofeng; Liu, Feng; Chen, Jiamin] Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Hubei, Peoples R China.;[Luo, Xiaofeng] Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90095 USA.;[Nara, Yasushi] Akita Int Univ, Akita 0101292, Japan.;[Nara, Yasushi] Frankfurt Inst Adv Studies, D-60438 Frankfurt, Germany.
关键词：
heavy-ion collisions;elliptic flow;equation of state;QCD phase transition
摘要：
We perform a systematic study of elliptic flow (v_2)in Au+Au collisions at √S_(NN)=5 GeV by using a microscopic transport model, JAM. The centrality,pseudorapidity, transverse momentum and beam energy dependence of v_2 for charged as well as identified hadrons are studied. We investigate the effects of both the hadronic mean-field and the softening of equation of state (EoS) on elliptic flow. The softening of the EoS is realized by imposing attractive orbits in two body scattering, which can reduce the pressure of the system. We found that the softening of the EoS leads to the enhancement of v_2, while the hadronic mean-field suppresses v_2 relative to the cascade mode. It indicates that elliptic flow at high baryon density regions is highly sensitive to the EoS and the enhancement of V_2 may probe the signature of a first-order phase transition in heavy-ion collisions at beam energies of a strong baryon stopping region.
作者机构：
[Luo, Xiaofeng; Zhang, Chao; Liu, Feng; Chen, Jiamin] Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Hubei, Peoples R China.;[Luo, Xiaofeng; Zhang, Chao; Liu, Feng; Chen, Jiamin] Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Hubei, Peoples R China.;[Nara, Yasushi] Akita Int Univ, Akita 0101292, Japan.;[Nara, Yasushi] Frankfurt Inst Adv Studies, D-60438 Frankfurt, Germany.
通讯机构：
[Luo, Xiaofeng] C;Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Hubei, Peoples R China.;Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Hubei, Peoples R China.
摘要：
We present a detailed analysis of the beam energy dependence of the mechanisms for the generation of directed and elliptic flows in Au + Au collisions focusing on the role of hadronic rescattering and spectator shadowing within a microscopic transport model jam with different equations of state. A systematic study of the beam energy dependence is performed for Au + Au collisions at sNN=2.3−62.4 GeV. The transition of the dynamical origin of the directed flow is observed. We find that the initial Glauber-type nucleon-nucleon collisions generate negative v1 for nucleons at midrapidity due to the presence of spectator matter, and this negative nucleon v1 is turned to be positive by the meson-baryon interactions at the beam energy region of sNN<30 GeV. In contrast, above 30 GeV there is no spectator shadowing at midrapidity, and initial nucleon-nucleon collisions do not generate directed flow, but subsequent rescatterings among produced particles generate negative v1 for nucleons. It is demonstrated that negative pion-directed flows are mostly generated by the interaction with the spectator matter. It is also shown that the squeeze-out effect is largely suppressed in the case of softening, which leads to the enhancement of elliptic flow around sNN=5−7 GeV. The elliptic flow at midrapidity above 10 GeV is not influenced by the squeeze-out due to spectator matter, while its effect is seen at the forward rapidity range of y/yc.m.>0.5, which decreases as beam energy increases.
作者机构：
[Luo, Xiaofeng; Liu, Feng; Zhou, Chang; Xu, Ji] Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Peoples R China.;[Luo, Xiaofeng; Liu, Feng; Zhou, Chang; Xu, Ji] Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.;[Luo, Xiaofeng] Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90095 USA.
通讯机构：
[Luo, Xiaofeng] C;[Luo, Xiaofeng] U;Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Peoples R China.;Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.;Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90095 USA.
摘要：
Fluctuations of conserved quantities, such as baryon, electric charge, and strangeness number, are sensitive observables in heavy-ion collisions to search for the QCD phase transition and critical point. In this paper, we performed a systematical analysis on the various cumulants and cumulant ratios of event-by-event net-strangeness distributions in Au+Au collisions at sNN=7.7, 11.5, 19.6, 27, 39, 62.4, and 200 GeV from an ultrarelativistic quantum molecular dynamics model. We performed a systematical study on the contributions from various strange baryons and mesons to the net-strangeness fluctuations. The results demonstrate that the cumulants and cumulant ratios of net-strangeness distributions extracted from different strange particles show very different centrality and energy-dependence behavior. By comparing with the net-kaon fluctuations, we found that the strange baryons play an important role in the fluctuations of net strangeness. This study can provide useful baselines to study the QCD phase transition and search for the QCD critical point by using the fluctuations of net strangeness in heavy-ion collisions experiment. It can help us to understand noncritical physics contributions to the fluctuations of net strangeness.
摘要：
Anisotropic flow is an important observable in the study of the quark-gluon plasma that is expected to be formed in heavy-ion collisions. With a multiphase transport (AMPT) model we investigate the elliptic (v_2), triangular (v_3), and quadrangular (v_4) flow of charged particles in Pb+Pb collisions at √SNN = 5.02 TeV. We then compare our flow results with the published ALICE flow results. We find our AMPT simulated results are consistent with ALICE experimental data.
作者机构：
[Xiao, Kai; Liu, Feng; Wang, Fu-Qiang] Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Hubei, Peoples R China.;[Xiao, Kai; Liu, Feng; Wang, Fu-Qiang] Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Hubei, Peoples R China.;[Xiao, Kai; Liu, Feng] South Cent Univ Nationalities, Coll Elect & Informat Engn, Wuhan 430074, Hubei, Peoples R China.;[Wang, Fu-Qiang] Purdue Univ, Dept Phys, W Lafayette, IN 47907 USA.;[Wang, Fu-Qiang] Huzhou Univ, Sch Sci, Huzhou 313000, Zhejiang, Peoples R China.
通讯机构：
[Xiao, Kai] C;[Xiao, Kai] S;Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Hubei, Peoples R China.;Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Hubei, Peoples R China.;South Cent Univ Nationalities, Coll Elect & Informat Engn, Wuhan 430074, Hubei, Peoples R China.
关键词：
elliptic flow fluctuations;eccentricity;initial configuration;parton-parton interactions;hadronization and hadronic scatterings
摘要：
Sources of event-by-event elliptic flow fluctuations in relativistic heavy-ion collisions are investigated in a multiphase parton transport model (AMPT). Besides the well-known initial eccentricity fluctuations, several other sources of elliptic flow dynamical fluctuations are identified. One is fluctuations in initial parton configurations at a given eccentricity. Configuration fluctuations are found to be as important as eccentricity fluctuations in elliptic flow development. A second is quantum fluctuations in parton-parton interactions during system evolution. A third is fluctuations caused by hadronization and final-state hadronic scatterings. The magnitudes of these fluctuations are investigated relative to the eccentricity fluctuations and the average elliptic flow magnitude. The fluctuations from the latter two sources are found to be negative. The results may have important implications for the interpretation of elliptic flow data.
摘要：
Substantial experimental and theoretical efforts worldwide are devoted to explore the phase diagram of strongly interacting matter. At LHC and top RHIC energies, QCD matter is studied at very high temperatures and nearly vanishing net-baryon densities. There is evidence that a Quark-Gluon-Plasma (QGP) was created at experiments at RHIC and LHC. The transition from the QGP back to the hadron gas is found to be a smooth cross over. For larger net-baryon densities and lower temperatures, it is expected that the QCD phase diagram exhibits a rich structure, such as a first-order phase transition between hadronic and partonic matter which terminates in a critical point, or exotic phases like quarkyonic matter. The discovery of these landmarks would be a breakthrough in our understanding of the strong interaction and is therefore in the focus of various high-energy heavy-ion research programs. The Compressed Baryonic Matter (CBM) experiment at FAIR will play a unique role in the exploration of the QCD phase diagram in the region of high net-baryon densities, because it is designed to run at unprecedented interaction rates. High-rate operation is the key prerequisite for high-precision measurements of multi-differential observables and of rare diagnostic probes which are sensitive to the dense phase of the nuclear fireball. The goal of the CBM experiment at SIS100 (\(\sqrt{s_{NN}}=\) 2.7--4.9 GeV) is to discover fundamental properties of QCD matter: the phase structure at large baryon-chemical potentials ( \(\mu_B > 500\) MeV), effects of chiral symmetry, and the equation of state at high density as it is expected to occur in the core of neutron stars. In this article, we review the motivation for and the physics programme of CBM, including activities before the start of data taking in 2024, in the context of the worldwide efforts to explore high-density QCD matter.
作者机构：
[Luo, Xiaofeng] Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Peoples R China.;Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.
通讯机构：
[Luo, Xiaofeng] C;Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Peoples R China.
摘要：
Fluctuations of conserved quantities are sensitive observables to probe the signature of QCD phase transition and critical point in heavy-ion collisions. With the UrQMD model, we have studied the centrality and energy dependence of various order cumulants and cumulant ratios (up to fourth order) of net-proton, net-charge, and net-kaon multiplicity distributions in Au+Au collisions at sNN=7.7, 11.5, 19.6, 27, 39, 62.4, 200 GeV. The model results show that the production mechanism of the particles and antiparticles has significant impact on the cumulants of net-particles multiplicity distributions and shows strong energy dependence. We also made comparisons between model calculations and experimental data measured in the first phase of the beam energy scan (BES) program by the STAR experiment at the BNL Relativistic Heavy Ion Collider. The comparisons indicate that the baryon conservation effect strongly suppresses the cumulants of net-proton distributions at low energies and the nonmonotonic energy dependence for the net-proton κσ2 at the most central Au+Au collisions measured by the STAR experiment cannot be described by the UrQMD model. Since there has been no physics of QCD phase transition and QCD critical point implemented in the UrQMD, the model results provide us baselines and qualitative estimates about the noncritical background contributions to the fluctuations observables in heavy-ion collisions.
摘要：
Momentum-space azimuthal harmonic event planes (EP) are constructed from final-state midrapidity particles binned in transverse momentum (pT) in sNN=200 GeV Au+Au collisions in a multiphase transport (AMPT) model. The EP correlations between pT bins, corrected by EP resolutions, are smaller than unity. This indicates that the EP's decorrelate over pT in AMPT, qualitatively consistent with data and hydrodynamic calculations. It is further found that the EP correlations approximately factorize into single pT-bin EP correlations to a common plane. This common plane appears to be the momentum-space EP integrated over all pT, not the configuration-space participant plane (PP).
摘要：
We trace the development of azimuthal anisotropy (nu(n), n = 2, 3) via parton-parton collision history in two transport models. The parton nu(n) is studied as a function of the number of collisions of each parton in Au + Au and d + Au collisions at root s(NN) = 200 GeV. It is found that the majority of nu(n) comes from the anisotropic escape probability of partons, with no fundamental difference at low and high transverse momenta. The contribution to nu(n) from hydrodynamic-type collective flow is found to be small. Only when the parton-parton cross-section is set unrealistically large does this contribution start to take over. Our findings challenge the current paradigm emerged from hydrodynamic comparisons to anisotropy data. (C) 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
作者机构：
[Zhou, You] Univ Copenhagen, Niels Bohr Inst, Blegdamsvej 17, DK-2100 Copenhagen, Denmark.;[Feng, Zhao; Xiao, Kai; Liu, Feng] Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Peoples R China.;[Feng, Zhao; Xiao, Kai; Liu, Feng] Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.;[Xiao, Kai] South Cent Univ Nationalities, Wuhan 430074, Peoples R China.;[Snellings, Raimond] Univ Utrecht, POB 80000, NL-3508 TA Utrecht, Netherlands.
通讯机构：
[Zhou, You] U;[Liu, Feng] C;Univ Copenhagen, Niels Bohr Inst, Blegdamsvej 17, DK-2100 Copenhagen, Denmark.;Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Peoples R China.;Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.
摘要：
With a multiphase transport (AMPT) model we investigate the relation between the magnitude, fluctuations, and correlations of the initial state spatial anisotropy ɛn and the final state anisotropic flow coefficients vn in Au+Au collisions at sNN=200 GeV. It is found that the relative eccentricity fluctuations in AMPT account for the observed elliptic flow fluctuations, both are in agreement with the elliptic flow fluctuation measurements from the STAR collaboration. In addition, the studies based on two- and multiparticle correlations and event-by-event distributions of the anisotropies suggest that the elliptic-power function is a promising candidate of the underlying probability density function of the event-by-event distributions of ɛn as well as vn. Furthermore, the correlations between different order symmetry planes and harmonics in the initial coordinate space and final state momentum space are presented. Nonzero values of these correlations have been observed. The comparison between our calculations and data will, in the future, shed new insight into the nature of the fluctuations of the quark-gluon plasma produced in heavy ion collisions.
作者机构：
[Peng, G. X.; Xu, J. F.] Univ Chinese Acad Sci, Sch Phys, Beijing 101408, Peoples R China.;[Peng, G. X.] Inst High Energy Phys, Theoret Phys Ctr Sci Facil, Beijing 100049, Peoples R China.;[Hou, De-Fu; Liu, F.] Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Peoples R China.;[Hou, De-Fu; Liu, F.] Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.;[Chen, Lie-Wen] Shanghai Jiao Tong Univ, Dept Phys & Astron, Shanghai 200240, Peoples R China.
通讯机构：
[Peng, G. X.] U;Univ Chinese Acad Sci, Sch Phys, 380 Huaibeizhen, Beijing 101408, Peoples R China.
摘要：
A quark model with running coupling and running strange quark mass, which is thermodynamically self-consistent at both high and lower densities, is presented and applied to study properties of strange quark matter and structure of compact stars. An additional term to the thermodynamic potential density is determined by meeting the fundamental differential equation of thermodynamics. It plays an important role in comparatively lower density and ignorable at extremely high density, acting as a chemical-potential dependent bag constant. In this thermodynamically enhanced perturbative QCD model, strange quark matter still has the possibility of being absolutely stable, while the pure quark star has a sharp surface with a maximum mass as large as about 2 times the solar mass and a maximum radius of about 11 kilometers.
作者机构：
[Zhang, Liang; Wang, Fuqiang; Liu, Feng] Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Peoples R China.;[Zhang, Liang; Wang, Fuqiang; Liu, Feng] Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.;[Wang, Fuqiang] Purdue Univ, Dept Phys & Astron, W Lafayette, IN 47907 USA.
通讯机构：
[Zhang, Liang] C;Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Peoples R China.
摘要：
We investigate the survival rate of an initial momentum anisotropy (v2ini), not spatial anisotropy, to the final state in a multiphase transport (AMPT) model in Au+Au collisions at sNN=200 GeV. It is found that both the final-state parton and charged hadron v2 show a linear dependence versus v2ini{PP} with respect to the participant plane (PP). It is found that the slope of this linear dependence (referred to as the survival rate) increases with transverse momentum pT, reaching ∼100% at pT∼2.5 GeV/ c for both parton and charged hadron. The survival rate decreases with collision centrality and energy, indicating decreasing survival rate with increasing interactions. It is further found that a v2ini{Rnd} with respect to a random direction does not survive in v2{PP} but in the two-particle cumulant v2{2}. The dependence of v2{2} on v2ini{Rnd} is quadratic rather than linear.
作者机构：
Laboratory of Information Technologies, Joint Institute for Nuclear Research (JINR-LIT), Dubna, Russian Federation;GSI Helmholtzzentrum für Schwerionenforschung GmbH (GSI), Darmstadt, Germany;Institut für Kernphysik, Goethe Universität Frankfurt, Frankfurt, Germany;Department of Physics, Bose Institute, Kolkata, India;Marian Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland
摘要：
The paper shows the advances of research carroed out by the CBM (Compressed Barionic Matter) Collaboration at FAIR/GSI in Darmstadt.
作者机构：
[Yu, N.; Liu, F.] Cent China Normal Univ, MOE, Key Lab Quark & Lepton Phys, Wuhan 430079, Peoples R China.;[Yu, N.; Liu, F.] Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.;[Wu, K.] China Three Gorges Univ, Coll Sci, Yichang 443002, Peoples R China.
通讯机构：
[Yu, N.] C;Cent China Normal Univ, MOE, Key Lab Quark & Lepton Phys, Wuhan 430079, Peoples R China.
摘要：
Driven by the Beam Energy Scan (BES) program at the RHIC, researches and discussions on the QCD phase diagram have flourished recently. In order to provide a reference from microscopic transport models, we performed a systematic analysis, using a multiphase transport (AMPT) model for the particle yields and a statistical model (thermus) for the thermal fit, for Au + Au collisions at sNN=7.7–200 GeV. It is found that at a fixed collision centrality the chemical freeze-out parameter, temperature Tch, increases with collision energy and somehow saturates at certain values of Tch in collisions near sNN=10 GeV, indicating the limiting temperature in hadronic interactions; meanwhile the baryon chemical potential μB decrease with the collision energy. The saturation temperature is also found to be dependent on partonic interaction. At a given collision energy, it is found that both Tch and μB decrease towards more peripheral collisions in the grand canonical approach. The energy and centrality dependence of other chemical freeze-out parameters, strangeness chemical potential μS, strangeness undersaturation factor γS, and the volume of the fireball V are also presented in this paper. The chemical potential ratio μs/μB is also compared with lattice QCD calculation. The AMPT default model gives better descriptions on both the particle yields and the chemical freeze-out parameters than those from the AMPT string-melting model.
