标题： 早期热化和在BES、FAIR和NICA能区重离子碰撞中的剪切黏度与熵比 显示英文标题

标题： Early thermalization and shear viscosity to entropy ratio in heavy-ion collisions at energies of BES, FAIR and NICA

摘要： 在BES、FAIR和NICA能区的A+A碰撞中，通过微观模型计算研究了高激发富含重子物质的平衡化。研究表明，从碰撞初始阶段开始，系统演化可以近似为相对论流体动力学，尽管此时热密核物质还未达到局部平衡。 在火球演化过程中，提取的能量密度、净重子密度和净奇夸克密度被用作统计模型（SM）的输入，以计算系统的温度$T$、化学势$\mu_B$和$\mu_S$以及熵密度$s$。同时，这些参数也被用作具有周期性边界条件的盒子的输入，以研究无限核物质中的动量关联函数。 根据格林-库珀公式计算剪切粘度$\eta$。在所有能量下，剪切粘度与熵密度比在最大重子密度对应的时间点达到最小值。研究了该比率随$T, \mu_B, \mu_S$变化的规律，包括平衡和非平衡情况。 显示英文摘要

摘要： Equilibration of highly excited baryon-rich matter is studied within the microscopic model calculations in A+A collisions at energies of BES, FAIR and NICA. It is shown that the system evolution from the very beginning of the collision can be approximated by relativistic hydrodynamics, although the hot and dense nuclear matter is not in local equilibrium yet. During the evolution of the fireball the extracted values of energy density, net baryon and net strangeness densities are used as an input to Statistical Model (SM) in order to calculate temperature $T$, chemical potentials $\mu_B$ and $\mu_S$, and entropy density $s$ of the system. Also, they are used as an input for the box with periodic boundary conditions to investigate the momentum correlators in the infinite nuclear matter. Shear viscosity $\eta$ is calculated according to the Green-Kubo formalism. At all energies, shear viscosity to entropy density ratio shows minimum at time corresponding to maximum baryon density. The ratio dependence on $T, \mu_B, \mu_S$ is investigated for both in- and out of equilibrium cases.