KN势对中能重离子碰撞中K介子产生影响的研究

发布时间：2017-12-28 20:25

本文关键词：KN势对中能重离子碰撞中K介子产生影响的研究　出处：《沈阳师范大学》2017年硕士论文　论文类型：学位论文

更多相关文章： 重离子碰撞 对称能 集体流 KN势

【摘要】：核物质状态方程(EOS)一直都是核物理领域一个十分重要的课题。重离子碰撞中产生的K介子可以作为核反应中形成的高密核物质的一个有效探针,结合输运模型模拟可以提取出高密核物质状态方程的相关信息。目前人们对同位旋对称(中子、质子数目相同)核物质的状态方程已经有一定的了解,认为其具有“软”的性质,但对于同位旋不对称的核物质仍旧不是十分清楚。近年来随着研究的不断深入,同位旋非对称核物质的EOS渐渐引起了大家的关注,其中引起热议的便是其最大的不确定部分,即来自于密度依赖的对称能部分。通过对实验数据和输运模型的模拟相结合可以作为探究高密核物质状态方程的一个有效方法。本文首先对K介子以及国内外重离子碰撞领域运用的输运模型作以相关介绍,并在最近更新的极端相对论量子分子动力学(UrQMD)模型基础上,以中能区(入射能量为0.6-2.0GeV/nucleon)Au+Au碰撞为例,探究了时间步长对各种观测量(质子以及π介子的产额和集体流)的影响。发现观测量会不同程度的受到时间步长的影响,其对π介子相关观察量的影响更明显于对质子的作用。本文进一步在UrQMD模型中引入了K介子与核子间相互作用势(KN势),详细给出了KN势推导过程以及如何应用到现有模型当中。同样以中能区Au+Au碰撞为例,研究了KN势对K介子产额和直接流、椭圆流的影响。研究结果表明,KN势使得K~+和K~0介子与核子之间存在排斥作用,从而产生与核子反向的直接流。当考虑KN势后,能够更好的再现K介子集体流的实验数据。还研究发现了K~0/K~+产额比依赖于对称能的“软硬”,发现“软”的对称能给出的K~0/K~+产额比更高;入射能量越低时,K~0/K~+产额比对对称能的敏感性就越强。入射能量为0.8 GeV/nucleon时,K~0/K~+产额比对对称能的敏感性要高于π~-/π~+产额比。随着实验上对重离子碰撞过程中K介子相关观察量的进一步准确测量,以及输运模型的不断优化,可以在这一能量下,利用K介子对对称能进行合理有效的约束。
[Abstract]:The state equation of state of nuclear matter (EOS) has always been a very important subject in the field of nuclear physics. K mesons generated in heavy ion collisions can be used as an effective probe for high-density nuclear matter formed in nuclear reactions. Combined with transport model simulation, we can extract relevant information of high-density nuclear matter equation of state. At present, people have known a lot about the equation of state of isospin symmetry (the same number of neutron and proton), and think it has a "soft" nature, but for isospin asymmetric nuclear matter, it is still not very clear. In recent years, with the deepening of research, the EOS of isospin asymmetric nuclear materials has attracted more and more attention. The most uncertain part is the density dependent symmetric energy part. The combination of the experimental data and the simulation of the transport model can be used as an effective method to explore the state equation of high density nuclear matter. The transport model firstly by ion collision domain of K meson at home and abroad as well as heavy as related to, and in a recent update of the relativistic quantum molecular dynamics (UrQMD) model based on the energy region (incident energy 0.6-2.0GeV/nucleon) Au+Au collision as an example, to explore the time step to measure various views (proton and pion yield and collective flow effect). It is found that the observable measurements are affected by the time step in varying degrees, and the effect on the pion correlation observation is more obvious to the protons. In this paper, we further introduce the K meson and nucleon interaction potential (KN potential) in the UrQMD model, and give the detailed derivation of the KN potential and how to apply it to the existing models. The effects of KN potential on the K meson yield, direct flow and elliptical flow are also studied with the Au+Au collision in the middle energy region as an example. The results show that the KN potential rejects the K~+ and K~0 mesons and nucleons, resulting in a direct flow against the nucleon. When the KN potential is considered, the experimental data of the K meson collective flow can be reproduced. It is also found that the K~0/K~+ yield ratio is dependent on the "soft and hard" dependence of the symmetric energy. It is found that the K~0/K~+ yield ratio of the "soft" symmetry energy is higher; the lower the incident energy is, the more sensitive the K~0/K~+ yield ratio to the symmetry energy is. The incident energy is 0.8 GeV/nucleon, the sensitivity of K~0/K~+ yield ratio is higher than that of the symmetry energy ~-/ Pi Pi + yield ratio. With the further accurate measurement of K meson related observations in heavy ion collisions and the continuous optimization of transport models, we can use the K meson to reasonably and effectively constrain the symmetry energy.
【学位授予单位】：沈阳师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O571.6

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