Centrality and energy dependence of rapidity correlation patterns in relativistic heavy ion collisions

The centrality and energy dependence of rapidity correlation patterns are studied in Au+Au collisions by using AMPT with string melting,RQMD and UrQMD models.The behaviors of the shortrange correlation(SRC)and the long-range correlation(LRC)are presented clearly by two spatial-position dependent correlation patterns.For centrality dependence.UrQMD and RQMD give similar results as those in AMPT,i.,e., in most central collisions,the correlation structure is flatter and the correlation range is larger,which indicates a long range rapidity correlation.A long range rapidity correlation showing up in RQMD and UrQMD implies that patton interaction is not the only source of long range rapidity correlations.For energy dependence,AMPT with string melting and RQMD show quite different results.The correlation patterns in RQMD at low collision energies and those in AMPT at high collision energies have similar structures,i.e.aconvex curve.while the correlation patterns in RQMD at high collision energies and those in AMPT at low collision energies show fiat structures,having no position dependence.Long range rapidity correlation presents itself at high energy and disappears at low energy in RQMD,which also indicates that long range rapidity correlations may come from some trivial effects,rather than the parton interactions.     

Trace initial interaction from final state observable in relativistic heavy ion collisions

In order to trace azimuthal angle dependence of the initial interaction in ultra-relativistic heavy ion collision,two azimuthal multiplicity-correlation patterns - neighboring and fixed-to-arbitrary angularbin correlation patterns - are suggested.From the simulation of Au + Au collisions at √SNN = 200 GeV by using the Monte Carlo models RQMD with hadron re-scattering and AMPT with and without string melting,we observe that the correlation patterns change gradually from out-of-plane preferential one to inplane preferential one when the centrality of collision shifts from the central collision to peripheral collision,meanwhile the anisotropic collective flow v2 keeps positive in all cases.This regularity is found to be collision energy independent.The physics behind the two opposite trends of correlation patterns,in particular,the presence of out-of-plane correlation patterns at RHIC energy,are discussed.     

部分子相互作用与(S_(NN))~(1/2)=130GeV Au-Au碰撞中两粒子的横向动量关联(英文)

采用蒙特卡罗模型AMPT 究了(S_(NN))~(1/2)=130GeV Au Au碰撞中部分子相互作用对两粒子横向动量关联的影响,结果表明部分子相互作用对两粒子的横向动量关联有重要的贡献．还计算了AMPT模型中(S_(NN))~(1/2)=130GeV Au Au碰撞的两粒子横向动量关联与碰撞对心性的依赖关系并与来自STAR的实验数据进行了比较,发现AMPT的理论预言很好地符合实验数据．     

Trace initial interaction from final state observable in relativistic heavy ion collisions

In order to trace the initial interaction in ultra-relativistic heavy ion collision in all azimuthal directions, neighboring angular-bin multiplicity correlation pattern is suggested. From the simulation of Au+Au collisions at ?{s_NN }\sqrt {s_{NN} } = 200 GeV by using the Monte Carlo models RQMD with hadron re-scattering and AMPT with and without string melting, we observe that the correlation pattern changes gradually from out-of-plane preferential one to inplane preferential one when the centrality of collision shifts from central to peripheral. This regularity is found to be model and collision energy independent. The physics behind the two opposite trends of correlation pattern is discussed.     

RHIC能区Au+Au碰撞中HBT关联参数分析

利用相对论量子分子动力学模型RQMD,对RHIC能区s=200GeV/u Au+Au碰撞进行了2π干涉学分析,并讨论了HBT半径参数对横动量的依赖关系.研究表明,两粒子关联函数能够给出碰撞源在冻结时刻的时空拓扑信息,HBT半径参数能够较好地反映源的尺度和形状,但其对横动量的依赖关系并不能直接反映源的压缩性质,而是对粒子产生时源的空间–动量关联程度更为敏感.     

Pseudorapidity dependence of short-range correlations from a multi-phase transport model

Using a multi-phase transport model(AMPT) that includes both initial partonic and hadronic interactions, we study neighboring bin multiplicity correlations as a function of pseudorapidity in Au+Au collisions at (sNN)~(1/2) = 7.7- 62.4 GeV.It is observed that for (sNN)~(1/2) 19.6 GeV Au+Au collisions, the short-range correlations of final particles have a trough at central pseudorapidity, while for (sNN)~(1/2) 19.6 GeV AuAu collisions,the short-range correlations of final particles have a peak at central pseudorapidity. Our findings indicate that the pseudorapidity dependence of short-range correlations should contain some new physical information, and are not a simple result of the pseudorapidity distribution of final particles. The AMPT results with and without hadronic scattering are compared. It is found that hadron scattering can only increase the short-range correlations to some level, but is not responsible for the different correlation shapes for different energies. Further study shows that the different pseudorapidity dependence of short-range correlations are mainly due to partonic evolution and the following hadronization scheme.     

Probing the QCD phase boundary with elliptic flow in relativistic heavy ion collisions at STAR

We present measurement of elliptic flow, v ₂, for charged and identified particles at midrapidity in Au+Au collisions at $\sqrt {s_{NN} } $ = 7.7?C39 GeV. We compare the inclusive charged hadron v ₂ to those from transport model calculations, such as the UrQMD model, AMPT default model and AMPT string-melting model. We discuss the energy dependence of the difference in v ₂ between particles and anti-particles. The v ₂ of ? meson is observed to be systematically lower than other particles in Au+Au collisions at $\sqrt {s_{NN} } $ = 11.5 GeV.     

Novel rapidity dependence of directed flow in high-energy heavy-Ion collisions

For high-energy nucleus-nucleus collisions, we show that a combination of space-momentum correlations characteristic of radial expansion, together with the correlation between the position of a nucleon in the nucleus and its stopping, results in a very specific rapidity dependence of directed flow: a reversal of sign in the midrapidity region. We support our argument by RQMD model calculations for Au+Au collisions at sqrt[s] = 200A GeV.     

Partonic interactions and two particle transverse momentum correlations in Au + Au collisions at √sNN=130GeV

Partonic effects on two-particle transverse momentum correlations are studied for Au+Au collisions at \sqrt{s_{_{\rm NN}}}=130GeV in the Monte Carlo model, AMPT. This study demonstrates that in these collisions partonic interactions contribute significantly to the correlations. Additionally, model calculations are compared with data of the two-particle transverse momentum correlations measured by the STAR Collaboration at RHIC, and it is found that AMPT with string melting can well reproduce the measured centrality dependence of the two-particle transverse momentum correlations in Au+Au collisions at \sqrt{s_{_{\rm NN}}}=130GeV.     

RHIC能区Au+Au非对心碰撞中的事件形状

利用相对论量子分子动力学模型RQMD,结合2π干涉学分析,对RHIC能区s=200AGeV Au+Au非对心碰撞的事件形状进行了研究.研究表明,HBT参数可以反映事件在坐标空间的非对称性,而不能直接给出事件在动量空间的压力梯度.另外,HBT参数对横动量的依赖关系对系统的空间–动量关联较为敏感.     

Is constituent quark scaling a unique sign of parton recombination?

We study the transverse momentum dependence of the anisotropic flow v₂ for π, K, nucleon, Λ, Ξ and Ω for Au+Au collisions at within two independent string-hadron transport approaches (RQMD and UrQMD). Although both models reach only 60% of the absolute magnitude of the measured v₂, they both predict the particle-type dependence of v₂ as observed by the RHIC experiments: v₂ exhibits a hadron-mass hierarchy in the low p_T region and a number-of-constituent-quark (NCQ) dependence in the intermediate p_T region. The failure of the hadronic models to reproduce the absolute magnitude of the observed v₂ indicates that transport calculations of heavy-ion collisions at RHIC must incorporate interactions among quarks and gluons in the early, hot and dense phase. The presence of an NCQ scaling in the string-hadron model results suggests that the particle-type dependences observed in heavy-ion collisions at intermediate p_T might be related to the hadronic cross sections in vacuum rather than to the hadronization process itself.     

Partonic effect on anisotropic flows of Ω baryon for Au+Au at 62.4 and 200 GeV/c

The elliptic flow v₂ and the fourth order anisotropic flow v₄ of (Ω+Ω̄) have been studied in the framework a parton–hadronic transport model, namely a multi-phase transport (AMPT) model, for ¹⁹⁷Au+¹⁹⁷Au collisions at = 200 GeV and 62.4 GeV. The transverse momentum (p_T) and the transverse kinetic energy (m_T-m₀) dependence of v₂ and v₄ are presented. The calculation in the AMPT model seems consistent with the STAR data. The results show that the v₂ of (Ω+Ω̄) in 200 GeV obeys the constituent quark number scaling that has been observed for other mesons and baryons. Comparison of (Ω+Ω̄) elliptic flow v₂ in the default version of AMPT, the melting version of AMPT and the RQMD model calculation, shows that the parton cascade process is important to reproduce the sizeable v₂, and the string melting AMPT model preferably reproduces (Ω+Ω̄) elliptic flow v₂ in ¹⁹⁷Au+¹⁹⁷Au collisions at = 200 GeV. The v₂ of (Ω+Ω̄) in the 62.4 and 200 GeV collisions seem similar, and the p_T dependence of (Ω+Ω̄) baryons’ v₄ in 62.4 GeV and 200 GeV looks also similar in the string melting AMPT model, which indicates that a similar partonic matter phase has been reached in both energies.     

相对论重离子碰撞中HBT关联λ参数分析(英文)

利用相对论量子分子动力学模型 RQMD,对 RHIC能区 s =2 0 0 AGe VAu+ Au中心碰撞进行了 2 π干涉学分析,对 HBT关联相干因子 λ的行为进行了研究 .研究表明 ,参数 λ一般小于理想混沌源时的值,这反映了源的部分相干特性外 ,还与源的膨胀和持续冻结有关 ,体现为 λ参数对粒子的冻结时间较为敏感.Using the dynamical transport model RQMD with a correlation after burner, the behavior of two pion HBT λ parameter is studied in Au+Au central collisions at RHIC energy s=200 A GeV. The λ parameter is found to be sensitive to the sequential freeze out in heavy ion collisions.     

Centrality dependence of pT spectra for identified hadrons in Au+Au and Cu+Cu collisions at √SNN=200 GeV

The centrality dependence of transverse momentum spectra for identified hadrons at midrapidity in Au+Au collisions at √SNN=200GeV is systematically studied in a quark combination model.The pT spectra of π±,K±,P(p-)and A(A)in different centrality bins and the nuclear modification factors(Rcp)for these hadrons are calculated.The centrality dependence of the average collective transverse velocity(β(r)) for the hot and dense quark matter is obtained in Au+An collisions,and it is applied to a relative smaller Cu+Cu collision system.The centrality dependence of pT spectra and the Rcp for π0,K0/s and A in Cu+Cu collisions at √SNN=200 GeV are well described.The results show that(β(r))is only a function of the number of participants Npart and it is independent of the collision system.     

Centrality, azimuthal and rapidity dependence of two-particle transverse-momentum correlation in relativistic heavy ion collisions

The centrality, azimuthal and rapidity dependence of two-particle transverse-momentum correlations are studied for Au-Au collision at 200 GeV using RQMD (relativistic quantum molecular dynamics) with and without final hadron re-scattering models. The influences of the re-scattering effects on the measured correlations are discussed. The results are compared with those from current heavy ion experiments.     

RHIC能区Au+Au碰撞中椭圆流的横半径依赖

用RQMD模型模拟了质心系束能量为s_NN=200GeV的Au+Au非对心碰撞, 研究了椭圆流对末态粒子冻出位置的关系. 研究表明, 随着冻出半径的增加, 椭圆流逐渐增强, 在源的初始表面处达到最大值, 随着冻出半径的继续增加, 椭圆流逐渐减小. 椭圆流的这种变化趋势反映了随着半径的增加, 压力梯度在各个方向上不同的变化. 本文提出了利用平均径向速度分析压力梯度的方法.     

Jozsó's Legacy: Chemical and kinetic freeze-out in heavy-ion collisions

We review J. Zimányi's key contributions to the theoretical understanding of dynamical freeze-out in nuclear collisions and their subsequent applications to ultra-relativistic heavy-ion collisions, leading to the discovery of a freeze-out hierarchy where chemical freeze-out of hadron yields precedes the thermal decoupling of their momentum spectra. Following Zimányi's lines of reasoning we show that kinetic freeze-out necessarily leads to a dependence of the corresponding freeze-out temperature on collision centrality. This centrality dependence can be predicted within hydrodynamic models, and for Au+Au collisions at RHIC this prediction is shown to reproduce the experimentally observed centrality dependence of the thermal decoupling temperature, extracted from hadron momentum spectra. The fact that no such centrality dependence is observed for the chemical decoupling temperature, extracted from the hadron yields measured in these collisions, excludes a similar kinetic interpretation of the chemical decoupling process. We argue that the chemical decoupling data from Au+Au collisions at RHIC can only be consistently understood if the chemical freeze-out process is driven by a phase transition, and that the measured chemical decoupling temperature therefore measures the critical temperature of the quark-hadron phase transition. We propose additional experiments to further test this interpretation.     

Centrality,azimuthal and rapidity dependence of two-particle transverse-momentum correlation in relativistic heavy ion collisions

The centrality, azimuthal and rapidity dependence of two-particle transverse-momentum correlations are studied for Au-Au collision at 200 GeV using RQMD （relativistic quantum molecular dynamics） with and without final hadron re-scattering models. The influences of the re-scattering effects on the measured correlations are discussed. The results are compared with those from current heavy ion experiments.     

Identified baryon and meson distributions at large transverse momenta from Au + Au collisions at square root sNN=200 GeV

Transverse momentum spectra of pi+/-, p, and p up to 12 GeV/c at midrapidity in centrality selected Au + Au collisions at square root sNN=200 GeV are presented. In central Au + Au collisions, both pi +/- and p(p) show significant suppression with respect to binary scaling at pT approximately >4 GeV/c. Protons and antiprotons are less suppressed than pi+/-, in the range 1.5 approximately < pT approximately < 6 GeV/c. The pi-/pi+ and p/p ratios show at most a weak pT dependence and no significant centrality dependence. The p/pi ratios in central Au + Au collisions approach the values in p + p and d + Au collisions at pT approximately >5 GeV/c. The results at high pT indicate that the partonic sources of pi+/-, p, and p have similar energy loss when traversing the nuclear medium.     

Backward yields of pions,protons, and deuterons in relativistic 28Si+Pb collisions at 14.6 A GeVc

The production of pions, protons and deuterons is studied at a laboratory angle of 144° in ²⁸Si+Pb collisions at 14.6 GeV/c per nucleon. The centrality dependence of the pion yields is studied over the full impact parameter range using a zero degree calorimeter. The results are compared with the hadronic cascade model RQMD. These calculations are generally in agreement with the experimental results. According to these calculations, the pion yield in our acceptance is completely dominated by Δ-decay at freeze-out. Our measurements thus support the importance of baryon resonance production as one of the central features of relativistic heavy ion collisions at AGS energies. Although the strength of the pion spectrum is adequately described for kinetic energies above 50 MeV, an additional very soft component is observed in the pion spectra which is not predicted by RQMD. This very soft component accounts for a significant fraction of the total pion yield in this rapidity range but remains unexplained.