【作者】 钟洋；

【导师】 冯笙琴；

【作者基本信息】 三峡大学 ， 凝聚态物理， 2010， 硕士

【摘要】 随着相对论重离子对撞机(RHIC)的大量有重要研究意义实验数据的发表和公布,和更高能量的大强子对撞机(LHC)即将运行,相对论重离子碰撞研究已经成为21世纪一个有重大研究意义的前沿研究领域之一。RHIC和LHC要解决的重大问题之一是:碰撞所产生的物质热化到什么程度?RHIC和LHC能产生极端高温高密的物质以及数目巨大的粒子数,这种极端高温高密的物质有许多问题需要我们去探索,在什么情况下这种物质处于局部或者整体热平衡?能否用一些热力学量,例如温度、压强和能量来表征它们的特征和怎样表征它们的特征?这些高温高密物质相空间分布具有怎样的特征?如何更详细讨论这种热物质的状态方程以及状态之间的转化?核几何对这些碰撞特征有什么影响?近期,许多理论和实验物理学家注意到:集体流特性研究已成为研究相对论重离子碰撞的多强子产生的一个重要研究工具,这是由于高能重离子碰撞所产生的纵向和横向流有丰富的物理内涵,它与系统的早期演化和核阻止特性有紧密的联系。可以用集体流来研究相对论重离子碰撞产生的核阻止和一些集体运动特征,通过分别对热解冻时,净质子和奇异粒子的相空间特征的研究,将会加深我们对重离子碰撞动力学机制的了解和认识。非均匀集体流模型(Non-Uniform Flow Model NUFM)认为:净重子快度分布出现中心下凹现象可能与纵向相空间非均匀分布特性有关,也即是:随着碰撞能量的升高,不仅会出现较强的纵向(与横向比较),导致有圆柱状的相空间分布特征,而且,由于末态产生粒子还带有母核的运动学特征,在纵向分布的发射源会集中分布在大快度区间.集体流分布在纵向会出现非均匀分布特征,在纵向出现的非均匀分布将导致中心下凹现象。本文的主要工作是利用NUFM,并考虑重子数守恒的修正,系统分析了A GS、SPS和RHIC能区的净质子分布特征.我们发现:对于RHIC能区,考虑到重子数守恒修正后,分布特征与不考虑分布完全不同。考虑重子数守恒,很显然是对原NUFM理论一个重要且合理的一个修正.原来没有考虑重子数守恒的NUFM在考虑RHIC能区上是有缺陷的,特别是在远离中心快度区间的区间,实验上还没有给出该快度区间的分布结果,且RHIC能区的动力学区间比A GS和SPS要宽许多,这一点已被实验所证实.文章预言该区域呈现峰状,这样的结论将有待更新的实验结果验证。并在此基础上分析了从AGS到RHIC能区的核阻止特性随入射粒子快度关系。本文最为重要的一项工作,通过系统分析A GS、SPS和RHIC能区的净质子分布特征和核阻止特性,在此工作基础上,预言LHC能区的净质子分布和核阻止本领。当然,这项研究还需等待LHC实验结果的检验。本文还根据非均匀流理论系统分析了SPS能区的奇异粒子分布特征,以及纵向流平均速度βγ随入射能量变化关系。更多还原

【Abstract】 With the running of Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider(LHC) , relativistic heavy ion collisions have been one of the most important research area. Several of the most important questions that RHIC and LHC should be answered are: what is the degree of thermalization of that LHC can reach? What is the situation of the produced matter to reach local equilibrium? How to express the thermalization feature of the system by using the thermalization quantity such as temperature, pressure and energy? What is the feature of the phase space of the material of high temperature and high density? How to investigate the equation of state and the transition between the hadron and QGP?and how to study the effect of collision on nuclear geometry ?The study of collective flow in high energy nuclear collisions has attracted increasing attentions from both experimental and theoretical points of view. The physics of longitudinal and transverse flows is due to their system evolution at early time and nuclear stopping. In general, the collective evolution of the hot and dense matter leaves a distinct imprint on the phase space distribution of the fireball at freeze-out. To disentangle such information from features generated during freeze-out, a refined understanding of the decoupling process is needed.Non-Uniform Flow Model (NUFM) realized that central dip of net proton distribution is closely related to the non-uniform feature of longitudinal phase space. As the incident energy increase, the transparency/stopping of relativistic heavy-ion collisions should be taken into account more carefully. A more reasonable assumption is that the fireballs keep some memory on the motion of the incident nuclei, and therefore the distribution of fireballs, instead of being uniform in the longitudinal direction, is more concentrated in the direction of motion of the incident nuclei, i.e. more dense at large absolute value of rapidity. It will not only lead to anisotropy in longitudinal-transverse directions, but also render the fireballs (especially for those baryons) distributing non-uniformly in the longitudinal direction. NUFM may analyze the central dip of baryon rapidity distribution by assuming that the centers of fireballs are distributed non-uniformly in the longitudinal phase space.We have ever used NUFM to study the net proton rapidity among AGS, SPS and RHIC energy regions. But for the RHIC energy regions, we made a mistake before to predict the distributions of net proton distributions since we neglected the effects of the baryon number conservation. Therefore, it is necessary to reanalyze the features of net proton rapidity distributions among AGS to RHIC by taking into account the baryon number conservation. It is found that when we consider the baryon number conservation, the features of the distributions at RHIC are completely different from the results given before , especially at large absolute rapidity region.With the run of forthcoming LHC, the predictions of the features of net proton rapidity distributions at LHC are also important. We will restudy the features of net proton rapidity distributions among AGS to RHIC by using NUFM, and make prediction for the features of forthcoming LHC in this paper.The strange particle distributions are also investigated by using NUFM during the SPS energy region. The dependence of the number of strange particles and the velocity of longitudinal flow on incident energies is also studied in this paper.更多还原