基于关联度的高阶集合流关联分析方法

基于关联度概念,建立了可以分别检测高阶集合流的方位角关联、横向动量模关联和横向关联的新方法.采用新方法分别分析了1.2A GeV Ar+BaI₂碰撞的Bevalac流光室4π实验事件中末态粒子分布的方位角关联与粒子横向动量模的关联对高阶集合流关联的贡献.研究表明:对于这组碰撞实验,末态粒子分布的方位角关联相对横向动量模的关联在高阶集合流关联中起主要作用;末态粒子横向动量模的关联不但可以使粒子群高阶关联的强度有所增加,而且还为在更为狭窄的区间上确定集合流集体性的范围提供了重要信息.     

重离子碰撞中的横向非对称流与多粒子方位角关联

非对心重离子碰撞中,横向非对称核物质流的存在引起了末态的多粒子方位角关联.对600A MeV Au+Au碰撞的QMD模拟数据分析表明,不同事件中侧向流与椭圆流在横向上的夹角存在明显的涨落,多粒子方位角关联揭示了相互作用区域核物质运动的空间–动量相关性.椭圆流对碰撞系统的演化过程反映敏感,在中间快度区域,不同事件中椭圆流的差别与反应过程中粒子经历再散射的情况有关.     

相对论重离子碰撞中集合流的横向运动关联

本文对1.2AGeV Ar+BaI₂和2.1 AGeV Ne+NaF碰撞的Bevalac流光室4π实验数据进行了集合流横向运动关联特性的研究.研究表明,末态粒子的横向运动不仅存在粒子分布的方位角关联,而且还存在横向动量模的关联;Ar+BaI₂碰撞实验中粒子分布的方位角关联、横向动量模关联和横向运动关联都分别强于Ne+NaF碰撞实验中相对应的各种关联;对于这两组碰撞实验,粒子分布的方位角关联相对横向动量模关联在横向运动关联中起着主要作用.     

高能重离子碰撞中末态粒子分布的非对称性

对Bevalac1.2A GeV Au+Au碰撞实验,根据以流方向为z轴的质心坐标系中末态粒子方位角分布的非对称性为极小的条件,确定了事件中五种质量范围(A=1,2,3,4,5-8)末态粒子的集合侧向流流角.在以流方向为z轴的质心坐标系中研究了不同质量末态粒子极角分布,结果表明质量越大的粒子在流方向分布得越集中,侧向流的“流”值越大.     

高能重离子碰撞中的集体流与空间-动量关联

高能重离子碰撞中,末态粒子的侧向流与椭圆流间存在方位角集体关联,该关联对反应中集体流的性质反映敏感.碰撞时,系统在坐标空间的演化与动量空间的演化过程相互影响,表现出明显的空间-动量关联.不同事件中椭圆流形式的差别与此空间-动量关联有关,反映了系统演化过程的涨落.     

中能重离子碰撞中的各向异性流标度

用同位旋相关的量子分子动力学(IQMD)模型, 研究了25MeV/A的⁸⁶Kr+¹²⁴Sn碰撞系统在较大碰撞参数下的轻碎片的各向异性流(v₂和v₄), 发现横向动量依赖的椭圆流(v₂)存在对轻碎片核子数的标度律(number-of-nucleon scaling)现象, 以及不同轻碎片的v₄/v₂²比值都近似等于一个常数0.5. 这种标度律现象可以用核子层次碎片形成的组合(coalescence)模型来解释.     

QGP强子化的多粒子玻色–爱因斯坦关联分析

计算了由夸克–胶子等离子体(QGP)颗粒表面强子化所产生的π介子和K介子的多粒子玻色–爱因斯坦关联.对有限初始重子数密度的情况,K⁺介子的多粒子关联比π介子的多粒子关联弱,K^－介子的平均多粒子关联强度随QGP颗粒数目N_d的增加而快速下降.在零初始重子数密度情况下,K⁺和π介子的平均多粒子关联强度的差别随N_d的增加而变得明显.     

25MeV/u 40Ar+115In反应碎片和轻带电粒子的方位角关联

在25MeV/u ⁴⁰Ar+¹¹⁵In反应的在平面和出平面大角度关联测量中,提取了碎片和α粒子之间的方位角关联函数和方位角非对称性因子.φ=90°时,方位角关联函数呈现为最小值,表明在集体类转动效应影响下,反应产生的轻带电粒子和碎片优先在反应平面内发射.随着关联对质量的增加,在平面关联粒子的发射相对于束流轴不对称性逐渐增大.随着关联对质量的增加,相继衰变和粒子末态相互作用对φ=0°的关联粒子对方位角关联函数值的影响逐渐降低并直至消失,同时集体转动效应增强,方位角非对称性增加.     

基于Weiss分子场理论对极性液体中静态介电常数随温度变化及其相应取向关联的研究

迄今为止,并没有被普遍接受的液体静态介电常数的微观理论模型, 主要原因是对属于强关联系统的液体中分子之间的取向关联特征仍不十分清楚. 本文基于Weiss分子场理论(WMFT), 对水(water, H₂O)、甲醇(methanol, CH₄O)、乙醇(ethanol, C₂H₆O)和正丙醇(1-propanol, C₃H₈O)等4种极性液体中静态介电常数, 具体为Curie-Weiss常数、Curie温度和Weiss分子场因子随温度变化规律进行分析研究, 得出上述液体中: 1)铁电关联(ferroelectric correlation, FC)和反铁电关联(anti-ferroelectric correlation, AFC)共存, 且FC比AFC强得多, 以及随温度降低FC减弱和/或AFC增强; 2)结构均匀的WMFT不能定量描述上述液体中足够低的温度下反常大的静态介电常数. 可以想象FC和较弱AFC的共存必然导致极性液体中关联序的空间不均匀, 由此作者提出了空间不均匀关联序的粗粒近似的Weiss分子场理论, 并用此理论对上述液体中静态介电常数随温度快速变化的行为进行了解释. 上述结果对深入认知液体物理学, 包括玻璃化转变机制的探索, 无疑是有价值的.     

超相对论Au+Au碰撞中椭圆流的时间依赖

用相对论量子分子动力学(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时间的关系. 研究了在不同的阶段, 椭圆流对末态粒子位置的关系. 结果表明椭圆流随冻出时间的单调递减, 椭圆流对横向半径的关系随冻出时间发生变化. 用压力梯度对所得结果进行了分析. 径向速度用来表征压力梯度.     

Pion collectivity in relativistic heavy-ion collisions

The inelastic nucleon-nucleon cross section may be enhanced in the nuclear medium by pion collectivity. Empirical hamiltonians are on the borderline of strongly collective behavior, and the predicted enhancement factors range from 1–5 for various hamiltonians from the literature. An enhancement would have a substantial effect on the sideward flow in relativistic heavy-ion collisions. If this effect is present, the equation of state could be softer than in previous analyses.     

Sideward flow in Au+Au collisions between 2A and 8A GeV

Using the large acceptance Time Projection Chamber of experiment E895 at Brookhaven, measurements of collective sideward flow in Au+Au collisions at beam energies of 2A, 4A, 6A, and 8A GeV are presented in the form of in-plane transverse momentum and the first Fourier coefficient of azimuthal anisotropy v(1). These measurements indicate a smooth variation of sideward flow as a function of beam energy. The data are compared with four nuclear transport models which have an orientation towards this energy range. All four exhibit some qualitative trends similar to those found in the data, although none show a consistent pattern of agreement within experimental uncertainties.     

Radial, sideward and elliptic flow at AGS energies

We study the baryon transverse in-plane (sideward) and elliptic flow from SIS to AGS energies for AuAu collisions in a relativistic dynamical simulation model that includes all baryon resonances up to a mass of 2 GeV as well as string degrees of freedom for the higher mass continuum. There are two factors which dominantly determine the baryon flow at these energies: the momentum dependence of the scalar and vector potentials and the resonance-string degrees of freedom. We fix the explicit momentum dependence of the nucleon-meson couplings of NL3(hard) equation of state (EoS) by the nucleon optical potential up to 1 GeV of kinetic energy. We simultaneously reproduce the sideward flow, the elliptic flow and the radial transverse mass distribution of protons data at AGS energies. In order to study the sensitivity of different mean-field EoS, we use NL2(soft) and NL23(medium) along with NL3(hard) momenta-dependent mean-field EoS. We find that to describe data on both sideward and elliptic flow, NL3 model is better at 2 A·GeV, while NL23 model is at 4–8 A·GeV.     

CSR能区UU碰撞侧向流蒙特卡罗模拟与研究

应用ART模型研究了E_b=520MeV/u的UU碰撞. 探讨了在两种极端方位UU碰撞下, 核子和π在反应平面内的横向流的时间演化以及对碰撞中心度的依赖关系. 研究表明, 流在高密区域发展并且在膨胀相稳定, 因而它是高密区域反应动力学的一个敏感探针. 对头头和体体UU碰撞, 末态π相对于核子的横向流分别在大约b=9fm和b=2fm处存在明显的正向到负向的改变. π的这种行为是重子共振态和旁观者的遮蔽效应(再散射和再吸收)共同作用的结果.     

Monte-Carlo Simulation and Study of Sideward Flow for 238U238U Collisions at CSR Energy Area

The ART(a Relativistic Transport) Model is applied for studying the UU collisions at a beam kinetic energy about 0.52GeV/nucleon. We discuss the time evolution and the centrality dependence for sideward flow of nucleons and pions at two extreme orientation UU collisions. It is found that the collective (side) flow is developed in the high density region and has a saturation in the expansion phase, so it is a sensitive probe for the reaction dynamics in the high density region. A distinct transition from pion flow to antiflow, which is relative to nucleons flow, occurs at the impact parameters of about 8fm and 2fm in tip-tip and body-body UU collisions, respectively. The pion flow is a result of the competition between the collective flow of baryon resonances and the shadowing of spectators through rescatterings and reabsorptions.     

2.1AGeVNe NaF碰撞中的粒子群关联与集体性

提出了粒子群关联概念，并以此建立了一种检测集合流的新方法，采用新方法对２．１ＡＧｅＶＮｅ＋ＮａＦ碰撞的Ｂｅｖａｌａｃ流光室４π实验事件粒子群的关联进行了研究．通过与蒙特卡罗结果进行比较，推测该实验事件集合流的集体性约在７５％－９５％之间。     

Collective mechanism for nuclear stopping and transverse flow in heavy-ion collisions

The role of filamentation instability of quark-gluon plasma, in explaining collective phenomena in relativistic heavy-ion collisions, has been analyzed. Using equations of SU(2) two fluid color hydrodynamics it is shown that this instability can significantly enhance nuclear stopping and might contribute to collective sideward flows.     

Statistic and collective properties of the fireball formed in relativistic reactions of very massive ions

Some recent analyses performed with the FOPI Detector at GSI for the Au(150–600 AMeV)+Au reactions are presented and discussed. The emphasis is put first on the quality of the fireball selection. To this aim, several approaches are examined and compared. Different aspects of the fireball decay are presented. The thermal and chemical equilibrium of the fireball are examined and the baryonic entropy is determined. The extracted values depart from those of earlier measurements and agree well with hydrodynamic predictions. The collective flow (sideward and squeeze-out) is measured as a function of centrality, charge of the ejectiles and bombarding energy. Comparisons with quantum molecular dynamical model predictions are shown and discussed. The shape of the flow in the particular case of highly central reactions is presented. A transverse flow, mostly contained in the azimuthal plane, is evidenced for the first time. In all these analyses the relevance of the cluster measurements is underlined.     

Collective flows in high-energy heavy-ion collisions at AGS and SPS energies

Proton collective flows in heavy-ion collisions from AGS ((2–11) A GeV) to SPS ((40,158) A GeV) energies are investigated in a nonequilibrium transport model with nuclear mean-field (MF). Sideward (p _x), directedv ₁, and ellipticv ₂ flows are systematically studied with different assumptions on the nuclear equation of state (EoS). We find that momentum dependence in the nuclear MF is important for understanding the proton collective flows at AGS and SPS energies. Calculated results with momentum-dependent MF qualitatively reproduce the experimental data of proton sideward, directed, and elliptic flows in an incident energy range of (2–158) A GeV This talk is based on ref. [1]