利用重离子碰撞研究对称能的高密行为

发布时间：2018-04-29 14:06

本文选题：对称能 + 高密行为　；参考：《兰州大学》2016年博士论文

【摘要】：非对称核物质状态方程(特别是对称能的高密行为)的研究是当前核物理领域的热点之一,这一研究对于认识和理解核物理与核天体物理中许多物理问题和物理现象至关重要。重离子碰撞是目前实验室内可以形成高密非对称核物质从而用于研究对称能高密行为的唯一手段。由于实验上不能直接测量对称能,人们需要利用输运理论模型模拟重离子碰撞过程并与相应的实验观测量进行比较来间接提取对称能密度依赖性的相关信息。目前,中国、美国、德国、日本等国家的各大重离子实验室都将非对称核物质性质以及对称能高密行为的研究作为主要的物理目标。本论文在同位旋依赖的Boltzmann-Uehling-Uhlenbeck(IBUU)模型和极端相对论量子分子动力学(UrQMD)模型理论框架内,通过系统模拟中能重离子碰撞过程,研究了对称能的各种灵敏观测量,得到了一些有价值的结果,主要包括:研究并指出了π-/π+比、自由核子发射n/p比、质子和中子的集体流、中子-质子微分横向流等常用的对称能敏感观测量的模型依赖性;研究了高密对称能对核子的同位旋相分化的影响,提出高动能核子的正常和反常同位旋相分化可以作为模型无关的对称能高密行为的定性探针;讨论了介质中核子-核子弹性散射截面对域下π介子发射的影响,结果表明:具有相同质量数的丰中子系统和缺中子系统的π-/π+的双比可以消除介质中核子-核子弹性散射截面效应,而保留对称能效应;研究了π势对重离子碰撞中π介子发射的影响,结果表明:在较低束流能量下,由于π势的作用,对称能对π-/π+比的影响会减小;还进一步研究了?共振态势对π-/π+比和预平衡发射核子n/p比的影响,结果表明:?共振态势对预平衡发射核子n/p比几乎没有影响,而对π-/π+比有轻微的影响,而且,在采用软的对称能时,可以用核子的同位旋标量势代替?共振态势,从而避免??π反应道的能量不守恒问题。
[Abstract]:The study of asymmetric nuclear matter equation of state (especially the high density behavior of symmetric energy) is one of the hotspots in the field of nuclear physics. This research is very important for understanding and understanding many physical problems and phenomena in nuclear physics and nuclear astrophysics. Heavy ion collision is the only way to study symmetric energy and high density behavior in laboratory. Because the symmetry energy can not be measured directly in the experiment, it is necessary to simulate the heavy ion collision process by using the transport theory model and compare it with the corresponding experimental observations to extract indirectly the relevant information of the symmetry energy density dependence. At present, the major heavy ion laboratories in China, the United States, Germany, Japan and other countries have made the study of asymmetric nuclear matter properties and the high density behavior of symmetric energy as the main physical targets. Within the framework of the isospin dependent Boltzmann-Uehling-Uhlenbecking-IBUUU model and the ultra-relativistic quantum molecular dynamics (QMD) model, various sensitive measurements of symmetric energy are studied through the systematic simulation of energy heavy ion collisions. Some valuable results are obtained, including: the model dependence of the commonly used symmetric energy sensitive observations, such as 蟺-/ 蟺 ratio, free nucleon emission n / p ratio, collective flow of protons and neutrons, neutron differential transverse currents, etc. The effect of high density symmetric energy on the isospin differentiation of nucleon is studied. It is suggested that the normal and abnormal isospin differentiation of high kinetic energy nucleon can be used as a qualitative probe for the model-independent symmetric energy high density behavior. The effect of the nucleon-nucleon elastic cross section on the 蟺 meson emission in the medium is discussed. The results show that the 蟺-/ 蟺 double ratio of the rich and missing subsystems with the same mass number can eliminate the nucleon-nucleon elastic cross section effect in the medium, but retain the symmetric energy effect. The effect of 蟺 potential on 蟺 -meson emission in heavy ion collisions is studied. The results show that the effect of symmetry energy on 蟺-/ 蟺 ratio is reduced at lower beam energy, and the effect of symmetry energy on 蟺-/ 蟺 ratio is further studied. The effect of the resonance state on the 蟺-/ 蟺 ratio and the n / p ratio of the pre-equilibrium emission nucleon is obtained. The resonance state has little effect on the n / p ratio of the pre equilibrium emission nucleon, but has a slight effect on the 蟺-/ 蟺 ratio. Moreover, the isospin scalar potential of the nucleon can be replaced by the soft symmetric energy. Resonance state, thus avoiding the energy nonconservation of pion reaction channel.
【学位授予单位】：兰州大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O571.6

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