高能重离子碰撞中集体流的转动和极化研究

In high-energy heavy-ion collisions, collective flow is an important probe for detecting the properties of quark-gluon plasma (QGP). In recent years, as the intensive investigation on the properties of QGP, people show great interests on the rotation and polarization of collective flow, this also brings the new challenges for analying the features of the hot-dense flow in the early stage of nuclear collisions. The project was planned to analyze the rotation and polarization of collective flow of the final state of heavy ion collisions, by employing a hybrid model which combines the relativistic hydrodynamics model and microscopic transport model PACIAE. The core research topics and the goals of the project are as follows: 1) To analyze the construction and advantages of the hybrid model, consider the different initial states, explore the conditions and properties of collective flow with Kelvin-Helmholtz Instability (KHI), look for the best initial state model; 2) From the perspective of Lambda polarization and two-particle correlation, to quantitatively analyze the rotation and polarization of collective flow of the final state, so as to provide the theoretical method for experimental detection of the rotation and polarization. The researches of this project are not only beneficial for the understanding of the evolution process of high energy heavy-ion collisions from initial state to final state, but also provide some theoretical guidance on the heavy-ion collisions experimental detection of rotation and polarization of collective flow.

在高能重离子碰撞中，集体流是探测夸克胶子等离子体（QGP）性质的重要探针。近年来，随着对QGP性质的深入研究，人们对集体流的转动和极化产生了极大的兴趣，这也为研究核碰撞早期的热密流体性质提出了新的挑战。本项目拟利用相对论流体力学模型和微观输运模型PACIAE相结合的组合模型研究重离子碰撞末态集体流的转动和极化，重点研究内容和目标为：1)分析组合模型的构建并挖掘其优势，考虑不同的初态选择，探讨具有开尔文-赫姆赫兹不稳定性集体流的产生条件及其性质，寻找最佳初态模型；2)从Lambda粒子极化和两粒子关联视角，量化研究末态集体流的转动和极化，为实验测量提供理论方法。本项目的研究不仅有利于认识重离子碰撞中系统从初态到末态的演化，而且为重离子碰撞实验上探测集体流的转动和极化提供理论指导。

本项目主要从两方面开展研究工作：一是利用相对论3 +1D的流体力学模型研究重离子碰撞末态集体流的转动和极化，主要研究进展包括：1）发现模型中的纵向极化与实验观察到的横动量平面上四极结构具有类似的结果；2）发现由系统膨胀引起的第二项或相对论热旋度的时间分量对结果起着至关重要的作用；3）发现全局极化对快度没有显著的依赖性，这与实验结果一致。二是利用部分子-强子级联模型PACIAE研究了金核-金核在不同质心系能量碰撞下的涡旋与极化，主要研究进展包括：1）探究高能重离子碰撞中部分子流体涡旋演化对时间、碰撞能量和碰撞参数的依赖性和空间分布等性质；2）计算Λ超子的全局极化，研究PACIAE模型中Λ超子全局极化对碰撞能量、碰撞参数和时间截断的依赖性等性质；3）分析在LHC能量下的核-核对撞中，强子与其夸克成分的核修饰因子的对应关系以及部分子、强子层次的核修正因子味（质量）排序。