在重离子碰撞中的K－介子吸收对其产生的影响

用RBUU方法研究了中高能重离子碰撞中K^－介子产额及谱的情况.我们发现K⁺/K^－产额比是与核系统大小相关的,这种相关性与K^－介子在核介质中所受的吸收效应有关.还研究了在三种不同核系统中的K^－平均吸收路程,发现K^－平均吸收路程在轻核系统中与在中、重核系统中存在较大的差别,从而定量地解释了这种K⁺/K^－比与核系统的相关性.研究结果给出了核介质对K^－介子的吸收程度还与不同反应道的贡献有关,这是导致Bπ→K^－X道在核系统,特别是在轻、中量核系统中起重要作用的一个重要原因.     

高能核碰撞中的K+/π+比与次级碰撞效应

用程函近似分析在高能核碰撞中次级作用对K⁺/π⁺比的影响.计算表明,在K⁺/π⁺比中次级碰撞效应是重要的.     

相对论重离子碰撞中π介子椭圆流劈裂

近年来,美国布鲁克海文国家实验室的相对论重离子对撞机上正在进行着束流能量扫描实验, STAR国际合作组的研究人员发现π介子椭圆流劈裂与电荷不对称度存在着线性关系.该现象被认为是手征磁波效应的重要信号.本文基于拓展的多相输运模型,利用三味Nambu-Jona-Lasinio (NJL)模型研究了构成π⁺和π^-介子不同的夸克同位旋平均场势,为解释π介子椭圆流劈裂与电荷不对称度线性关系的实验现象提供了新思路,可为同质异素体碰撞以及致密星体中夸克物质同位旋效应研究提供理论依据.     

重离子碰撞中的矢量介子自旋排列

在非对心相对论重离子碰撞中,参与反应的系统具有巨大的轨道角动量,从而使产生的夸克胶子等离子体具有极强涡旋场,并通过自旋-轨道相互作用导致部分子的自旋极化,经过强子化导致重子的自旋极化以及矢量介子的自旋排列等可观测效应.矢量介子的自旋排列是指其自旋密度矩阵的00元素ρ00偏离1/3.在矢量介子衰变到两个赝标介子的过程中,衰变产物的极角分布只与ρ00有关,以此可以对自旋排列进行测量.理论研究表明,重离子碰撞过程中,重子的自旋极化反映了夸克自旋极化的时空平均效应,而矢量介子自旋排列则反映了夸克反夸克自旋极化的局域相空间关联.本文回顾了相对论重离子碰撞中矢量介子自旋排列的相关理论工作.重点以非相对论夸克融合模型为例,明确地计入夸克极化的相空间依赖性,展示了矢量介子自旋排列与夸克反夸克自旋极化特别是它们之间相空间关联的关系.本文还讨论了涡旋、电磁场、有效φ介子场以及它们的局域涨落对φ介子自旋排列的贡献,结果显示强作用场的时空关联效应是导致φ介子自旋排列的主要因素.矢量介子自旋排列为探索强相互作用物质和强相互作用场的性质提供了新途径.     

中高能重离子碰撞中的集体流性质

本文研究了在静态时不同势场下,标示核物质的核物质内部压强和束缚能对核物质密度的依赖关系.在同时考虑势场的动量相关和介质效应的情况下,通过BUU动力学计算,系统地研究了核物质流对碰撞参数和入射能量的依赖关系.通过对不同状态下的计算结果与实验值的比较,加深了对核物质状态方程的了解.     

重离子碰撞中的轻矢量介子光生过程(英文)

计算了相对论重离子碰撞中轻矢量介子(ρ,ω和φ)的光生过程。基于窄-宽近似,严格推导了相对论重离子碰撞中ρ,ω和φ半弹性和非弹性光生过程的遍举和单举横截面。从数值结果可以看出对于p-p碰撞,光生过程的贡献是不重要的,但是对于pT2.5 GeV Au-Au碰撞和pT3 GeV Pb-Pb碰撞,轻矢量介子光生过程的贡献是明显的。     

重离子碰撞中K介子和π介子产生的统一动力学模拟

用RVUU模型统一地研究了重离子碰撞中产生的K介子和π介子的动力学过程.考虑了K产生和输运过程的介质效应,同时,计入了π在核物质中的传播.用它模拟了每核子1GeV入射能量的重离子碰撞中π产生和阈下K产生过程.讨论了核介质效应对π末态性质的影响,以及对K末态性质的联带影响.计算结果表明,吸引的π光学势,影响了末态π动量分布,使横动量分布中具有小动量的π产额增大,同时明显增大了K的产额,改变了K的动量分布.这说明要合理地评价重离子碰撞的探测信息,需要统一地研究K和π的这些末态动力学作用.     

中能重离子碰撞动力学过程中的介质效应

本文对BUU方程碰撞项中的核子-核子碰撞截面分别采用有介质和无介质两种情况下的数据,系统地计算了重离子碰撞中介质效应对于集体流的影响.从有介质核碰撞截面和无介质核子碰撞截面随入射核子能量变化的规律合理地解释了介质效应对重离子碰撞横动量,流角等物理量的明显影响.分析这些影响可以看出在该能区和只考虑核子-核子弹性碰撞,π产生和π吸收的情况下介质效应与核物质状态方程的密切关系.     

KK强相互作用束缚态及K+K－原子态的研究

讨论了KK的强相互作用单介子交换势, 发现当考虑动量平方项时, 仅由单介子(ρ,ω,φ)交换势, 不足以构成束缚态. K⁺K^－在库仑势的作用下可以形成束缚态, 我们进一步计算了单介子交换势对K⁺K^－库仑势束缚态能级的影响以及K⁺K^－束缚态衰变到ππ和ηπ的宽度.     

重离子碰撞中的介子——兰州重离子冷却储存环上可能实验的讨论

讨论了在兰州重离子加速装置冷却储存环上开展介子产生的实验研究的可能性和进行π和η介子产生研究的意义在 ＣＳＲ能量区域内, 核子可以激发为Δ和 Ｎ,因此, 在研究热密核物质的状态方程时, 考虑Δ和Ｎ自由度是重要的． 观察重离子碰撞中产生的介子可以提供热密核物质的状态方程, 从而可以提供核内物质分布以及 Ｎ在核物质中传播的信息． 建议建造一个测量介子的实验装置, 以开展该领域的研究.The possibilities for experimental study of meson production at Cooling Storage Ring (CSR) of Lanzhou are discussed. It is shown that the study of production of the pion and eta mesons at CSR is of significance. Nucleon can be excited to Δ and N * at CSR energy region. Therefore, it is important to consider the degree of Δ and N * in the study of the equation of states of hot and dense matter. The produced mesons in heavy ion collisions can provide information on...     

Bose-Einstein Correlation of Kaon Pairs from Heavy-Ion Collisions at CERN Energy

The Bose-Einstein correlation of kaons from 160A GeV/c Pb + Pb collisions is analyzed within an event generator UR4SiMA. The theoretical results are in agreement with the preliminary data of NA44.     

Influence of Chiral Mean Field on Kaon In-plane Flow in Heavy Ion Collisions

The influence of the chiral mean field on the K⁺ in-planeflow in heavy ion collisions at SIS energy is investigated within covariant kaon dynamics. For the kaon mesons inside the nuclear medium a quasi-particle picture includingscalar and vector fields is adopted and compared to the standard treatment with a static potential. It is confirmed that a Lorentz force from spatial component of the vector field providesan important contribution to the in-medium kaon dynamics andstrongly counterbalances the influence of the vector potentialon the K⁺ in-plane flow. The calculated results show thatthe new FOPI data can be reasonably described using theBrown & Rho parametrization, which partly takes into accountthe correction of higher order contributions in the chiralexpansion. This indicates that one can abstract the informationon the kaon potential in a nuclear medium from the analysis ofthe K⁺ in-plane flow.     

来自夸克-胶子等离子体的弱磁辐射

在相对论重离子对撞中,必然有电磁场产生。尽管伴随夸克胶子等离子体演化的电磁场可能很弱,但它们有可能对电磁探针有重要意义。本工作首次提出了弱磁场和背景介质的纵向动力学的耦合效应。阐明了当夸克-胶子等离子体存在弱外部磁场时,由磁场诱导的光子是高度各向异性的。另一方面,来自夸克-胶子等离子体的弱磁光子发射对光子产量只有很小的修正。在具有倾斜构型的火球经流体动力学演化之后,可以很好地重现实验测量的直接光子椭圆流。同时,在流体动力学阶段使用的时间平均磁场不大于介子质量平方的百分之几。     

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]     

在pA碰撞中K~±,η和ф介子的阈下产生

简要评述了在pA碰撞过程中K±,η和ф介子的阈下产生及其对应的物理含义。这些介子的阈下产生都可以在兰州CSR上实现,特别是通过pA碰撞实现ф介子的阈下产生还没有看到实验数据的报道。     

用第一级反应平面测量重离子碰撞中逐事件椭圆流涨落的一种方法

A new method is presented for measuring event-by-event fluctuationsof elliptic flow (v₂) using first-order event planes.By studying the event-by-event distributions of v₂ observables and first-order event-plane observables, average flow〈v₂〉and event-by-event fluctuations with respect to thataverage can be separately determined, making appropriate allowancefor the effects of finite multiplicity. The relation of flow fluctuations to eccentricity fluctuations in the initial-state participant region, as well as detector acceptance effects, are discussed.     

J/ψ Dissociation in QGP via Multi-gluon Absorption

We propose that the suppression of J/ψ production in relativistic heavy ion collisions may be explained by that J/ψ dissociates via absorbing multi-gluons in the environment of quark-gluon-plasma (QGP) where abundance of gluons is expected.     

Finite-Size Effects on the Phase Diagram and Evolution of Strangelets in Ultrarelativistic Heavy-Ion Collisions

In the framework of multiple reflection expansion, finite-size effects are incorporated into the study of the phase diagram and evolution of a strangelet in equilibrium with a finite hadronic phase. It is found that in a significant way finite-size effects can modify the phase diagram and reduce the survival probabilities of cold strangelets in ultrarelativistic heavy-ion collisions. The inclusion of finite-size effects can also allow a quantitative analysis of the properties of a cold strangelet resulting from a smooth hydrodynamic evolution with equilibrium hadronization and isentropic expansion.     

Fragmentation in ^16 O-emulsion interactions at 3.7 A GeV

The topology of ¹⁶O fragmentation at 3.7 A GeV in reactions with emulsion nuclei is presented. The multiplicity distributions of projectile fragments,charged secondaries and their dependences on the projectile residues are discussed.     

Intermittency in 3.7 A GeV ^16O-emulsion interactions

The intermittency effect has been studied for an interaction of 3.7 A GeV ^16O with emulsion using the distributions of both the pseudorapidity intervals and the azimuthal angle intervals of the shower particles emitted in a central rapidity region. The scaled factorial moments, reduced scaled factorial moments and multifractal moments as functions of the bin size in pseudorapidity and in azimuthal angle have been calculated and have revealed the presence of an intermittent behaviour which may be due to the random cascading property of the reaction. The anomalous fractal dimension has been found to increase with the increase of rank of the moment.