高能重离子碰撞中颗粒与涨落非均匀源的多观测量分析

发布时间：2017-12-27 22:35

本文关键词：高能重离子碰撞中颗粒与涨落非均匀源的多观测量分析　出处：《大连理工大学》2016年博士论文　论文类型：学位论文

【摘要】：单粒子横动量谱、椭圆流和两粒子Hanbury-Brown-Twiss (HBT)关联是高能重离子碰撞实验的三个重要末态可观测量。它们从不同方面反映了碰撞产生的粒子发射源在不同时期的性质,因此对这三者进行联合研究能够对唯象的源模型给予很强的限制。通过对模型结果与实验数据的比较分析,人们在理解BNL的RHIC实验结果方面已取得了很大进展。最近,在CERN的LHC上进行的TeV能量重离子碰撞实验数据相继公布,系统并统一地解释RHIC和LHC两个能区重离子碰撞的多种末态可观测量的实验结果是对各种唯象模型的挑战。为解释RHIC能区的HBT之谜,人们提出并发展了流体力学演化的QGP颗粒源模型。本文中,我们在之前颗粒源工作的基础上进一步利用颗粒源模型研究RHIC和LHC能量下不同碰撞对心度重离子碰撞的多个末态可观测量。研究表明,颗粒源模型能够重现RHIC能区的Au+Au碰撞和LHC能区的Pb+Pb碰撞在不同碰撞对心度情况下的π介子横动量谱,椭圆流和HBT干涉学实验数据。其中,颗粒源模型参量随碰撞能量和碰撞对心度的变化展现出一定的规律。对这些规律的研究有助于人们了解RHIC和LHC两个能区重离子碰撞的粒子发射源的时空演化和动力学行为。在此基础上,我们改变颗粒源中的颗粒初始能量密度分布,并通过重现两个能区的实验数据,研究不同初始条件对颗粒源模型参数的影响。随着2015年RHIC能区K介子以及大横质量π介子HBT实验结果的发表,用统一的颗粒源模型对这些新的实验数据进行模拟分析是进一步检验和发展颗粒源模型的一个重要方面。由于K介子冻出的时间早,在颗粒源模型中早期从某个颗粒冻出的K介子在源内传播时有可能被其它颗粒吸收。为此我们在颗粒源模型中引入了一种对吸收效应的简单处理,研究了颗粒的吸收对K介子和π介子干涉学半径的影响。结果表明,所考虑的吸收对K介子的HBT半径有较大的影响,对π介子的HBT半径影响不大。在考虑了吸收效应后,颗粒源模型能够较好地同时重现K介子和π介子的HBT干涉学实验数据。近年来,粘滞流体力学在高能重离子碰撞研究中得以迅速发展。我们为此也将理想流体演化的QGP颗粒源模型进行推广。通过考虑颗粒流体演化的粘滞效应,我们发展了粘滞流体力学演化的QGP颗粒源模型,研究了粘滞效应对颗粒源模型末态π介子横动量谱、椭圆流和HBT半径结果的影响,并分析了理想和粘滞流体演化颗粒源模型参量的差异和变化。研究结果表明,QGP颗粒的剪切粘滞可以加速颗粒的流体演化,而体粘滞对颗粒演化的影响可以忽略。颗粒源模型下粘滞性对π介子横动量谱和椭圆流的影响不大,而对HBT半径Rout有较大影响,会使其变小。由于有粘滞性,颗粒源模型的初始颗粒半径参量会增加,而颗粒的初始速度参量和源的壳参量会减小。在高能重离子碰撞中,由于碰撞核中核子的位置分布存在随机涨落,同时每个核子中的夸克和胶子场也存在着量子涨落,因此核一核碰撞后的物质系统在尺寸、形状和密度分布上会呈现出逐事件涨落。随着系统的动力学演化,这些事件的初始空间几何涨落会转化为末态粒子动量空间方位角的各向异性。在本文最后,我们采用Monte Carlo Glauber (MC-Glauber)模型作为初始条件并结合(2+1)维粘滞流体力学演化,研究LHC能区的Pb+Pb碰撞情况下,从初态空间涨落到末态动量方位角各向异性的流体转化。研究表明,高能重离子碰撞初始涨落导致的不同阶初始几何偏心率εn之间存在关联,各阶εn与末态粒子相应阶的横动量流系数vn之间的转化并非是一对一的,各阶末态事件流平面角度之间也存在关联。初态不同阶几何偏心率之间的关联与相应不同阶初始参与平面角之间的关联会在流体演化过程中产生相互作用,共同推动导致末态的各向异性流。
[Abstract]:The single particle transverse momentum spectrum, elliptic flow and two particle Hanbury-Brown-Twiss (HBT) is associated with high energy heavy ion collision experiment three important final observables. They reflect the nature of the particle emission sources produced by collisions in different periods from different aspects. Therefore, the joint study of these three can impose a strong restriction on the phenomenological source model. By comparing the results of the model to the experimental data, people have made great progress in understanding the results of BNL's RHIC experiment. Recently, in the CERN LHC TeV energy heavy ion collision experimental data have been published, and a unified account of RHIC and LHC two kinds of final energy heavy ion collision observables experimental results on various phenomenological model challenges. In order to explain the riddle of HBT in the RHIC energy region, a QGP particle source model for the evolution of hydrodynamics is proposed and developed. In this paper, we base on the work of the particle source before further use of the granular source model study of RHIC and LHC energy under different collision to the heart of the heavy ion collision multiple final observables. The research shows that particle source model can reproduce the Pb+Pb collision of RHIC energy region Au+Au collision and LHC energy region, and the pion momentum spectrum, the experimental data of elliptical flow and HBT interference in different degrees of collision. The parameter of the particle source model shows a certain rule with the change of the collision energy and the impact on the degree of the heart. The study of these laws will help people understand the spatio-temporal evolution and dynamic behavior of the particle emission sources of heavy ion collisions in the two energy regions of RHIC and LHC. On this basis, we change the initial energy density distribution of particles in particle source, and reproduce the influence of different initial conditions on the parameters of particle source model by reconstructing the experimental data of two energy zones. With the publication of 2015 RHIC energy region K meson and large cross mass pion HBT experimental results, it is an important aspect to further examine and develop particle source models by using unified particle source model to simulate and analyze these new experimental data. As the K meson is frozen out early, the K meson that is frozen from a certain particle early in the particle source model may be absorbed by other particles when it is propagated from the source in the source. For this reason, we introduce a simple processing of absorption effect in particle source model, and study the influence of particle absorption on the interference radius of K meson and pion. The results show that the absorption of the K has a great influence on the HBT radius of the meson, and has little effect on the HBT radius of the pion. After considering the absorption effect, the particle source model can reproduce the HBT Interferometry Data of K meson and pion at the same time. In recent years, viscous fluid mechanics has developed rapidly in the study of high energy heavy ion collisions. Therefore, we also extend the QGP particle source model of the ideal fluid evolution. By considering the viscous effect of particle fluid evolution, we developed the QGP particle source evolution model of viscous fluid mechanics, study the influence of viscosity effect on the particle source model of final pion transverse momentum spectrum, elliptic flow and HBT radius results, and analyzes the ideal and viscous fluid play different particle source model parameters and changes. The results show that the shear viscosity of QGP particles can accelerate the fluid evolution of the particles, and the effect of body viscosity on the particle evolution can be ignored. Little effect on particle source model of viscosity on pion transverse momentum spectrum and elliptic flow, and has a great influence on the radius of HBT Rout, will become smaller. The parameters of viscosity, initial particle radius particle source model will increase, while the shell parameters of particles and the source parameters of the initial velocity will decrease. In high energy heavy ion collisions, collision of the Nucleon in nuclear distribution random fluctuations, while each nucleon quark and gluon field also exist quantum fluctuations, so the material system of nucleus nucleus collision will show fluctuations by event in size, shape and density distribution. With the evolution of system dynamics, the initial geometrical fluctuations of these events will be converted to the anisotropy of final particles in momentum space azimuth. At the end of this paper, we use the Monte Carlo Glauber (MC-Glauber) model as the initial conditions and combined with the (2+1) dimensional evolution of viscous fluid mechanics, Pb+Pb collision energy region of LHC, the transformation from initial state to the final state space fluid momentum fluctuation azimuthal anisotropy. The research shows that there is a correlation between the different order of initial geometric eccentricity n initial fluctuations in high energy heavy ion collisions caused by the transverse momentum of each order epsilon n final state particles and the corresponding order flow conversion coefficient between VN is not one to one, there is correlation between each order final event flow plane angle. The initial association between different geometric eccentricity and different initial order in association between the plane angle interact in fluid evolution process, and jointly promote the cause of anisotropy of final flow.
【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O571.6

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