费米动量对中能重离子碰撞椭圆流的影响  

Influence of Fermi momentum on elliptic flow in heavy-ion collisions at intermediate energies

作　　者：高波 王永佳[2] 李庆峰[2,3] 李保春[1] GAO Bo;WANG Yongjia;LI Qingfeng;LI Baochun(School of Physics and Electronics Engineering,The Shanxi University,Taiyuan 030006,China;School of Science,Huzhou University,Huzhou 313000,China;Institute of Modern Physics,Chinese Academy of Sciences,Lanzhou 730000,China)

机构地区：[1]山西大学物理电子工程学院,太原030006 [2]湖州师范学院理学院,湖州313000 [3]中国科学院近代物理研究所,兰州730000

出　　处：《核技术》2023年第7期69-77,共9页Nuclear Techniques

基　　金：国家自然科学基金(No.U2032145,No.11875125);国家重点研究开发计划(No.2020YFE0202002);山西省自然科学基金(No.202103021224036)资助。

摘　　要：椭圆流(v_2)是利用重离子碰撞探究核物质性质最重要的观测量之一,它的大小除了受到动力学过程的影响外,还与初态核子的费米动量有关。基于极端相对论量子分子动力学(Ultrarelativistic Quantum Molecular Dynamics,UrQMD)模型,通过反向追踪反应末态处在中心快度区(|y0|<0.1)的核子的v_2随时间的演化过程。探究初始时无费米动量、有费米动量和有一半费米动量对v_2演化的影响。以束流能量为0.4A GeV和0.8A GeV、碰撞参数为6 fm的金与金(Au+Au)碰撞为例,计算结果表明有费米动量时中心快度区的核子数远多于无费米动量的情况,这是由于不考虑费米动量时,核子-核子碰撞数目减少而导致。而v_2却表现出相反的效应,不考虑费米动量时的v_2更大,因为旁观核子有更强的阻止效应。这表明核子动量的初始化需要在输运模型中细致考虑。[Background]Elliptic flow(v2)is one of the most important observations for exploring the properties of nuclear matter using heavy-ion collisions.v2 is not only affected by dynamic processes but is also related to the Fermi momentum of the initial nucleus.[Purpose]This study aims to quantitatively determine the effect of the initial Fermi momentum on the time evolution of v2.[Methods]First,based on the Ultrarelativistic Quantum Molecular Dynamics(UrQMD)model,gold-gold(Au+Au)collisions at beam energies of 0.4A GeV and 0.8A GeV with impact parameter b=6 fm were simulated.In the initial stage,three cases were considered:without Fermi momentum,with Fermi momentum,and with half-Fermi momentum.Then,by reverse tracing the nucleons that were emitted at mid-rapidity(|y0|<0.1)throughout the reaction process,the time evolution of v2 for these traced nucleons was investigated in detail.Finally,the influence of the initial Fermi momentum on v2 of the nucleons in the mid-rapidity region in heavy-ion collisions at intermediate energies was examined.[Results]The yield of free nucleons calculated by considering the Fermi momentum was much larger than that obtained without the Fermi momentum,owing to the reduction in nucleon-nucleon collisions.However,v2 shows the opposite effect;it is obtained by considering that the Fermi momentum is much smaller than that in the latter case because of the stronger blocking effect of the spectator nucleons.[Conclusions]Our results indicate that the initialization of the nucleon momentum must be carefully considered in the transport model.

关 键 词：重离子碰撞 费米动量 椭圆流 

分 类 号：O571.6[理学—粒子物理与原子核物理]