FAIR能核碰撞的微观模型和有效状态方程
Microscopic models and effective equation of state in nuclear collisions at FAIR energies
摘要：
采用UrQMD和QGSM两种微观模型研究了能量为11.6 ~ 160 AGeV的重离子碰撞中局部平衡的热密核物质的形成.对体积为V = 125 fm**3的固定中心立方晶胞和遵循具有均匀分布的能量的中心区域的生长的膨胀晶胞进行分析。为了确定是否达到平衡，将微观计算的结果与统计热模型的结果进行比较。这两种动力学模型都表明，在任何轰击能量下，经过一定的弛豫时间后，都接近于动力学、热力学和化学平衡状态。能量越高，弛豫时间越短。状态方程具有简单的线性关系P = a（sqrt{s}）*e，其中a = c_s**2是声速的平方。它从E_{lab} = 11.6 AGeV时的0.12 \pm 0.01变化到E_{lab} = 160 AGeV时的0.145 \pm 0.005。a（sqrt{s}）行为的斜率变化发生在E_{lab} = 40 AGeV处，可以归因于从重子富集物质到介子主导物质的转变。在T-mu_B平面上的相图显示了沿着每个重子的等熵线的扭结的存在。这些扭结与系统中的非弹性（即化学）冻结有关。
英文摘要：
Two microscopic models, UrQMD and QGSM, were employed to study the formation of locally equilibrated hot and dense nuclear matter in heavy-ion collisions at energies from 11.6 AGeV to 160 AGeV. Analysis was performed for the fixed central cubic cell of volume V = 125 fm**3 and for the expanding cell which followed the growth of the central area with uniformly distributed energy. To decide whether or not the equilibrium was reached, results of the microscopic calculations were compared to that of the statistical thermal model. Both dynamical models indicate that the state of kinetic, thermal and chemical equilibrium is nearly approached at any bombarding energy after a certain relaxation period. The higher the energy, the shorter the relaxation time. Equation of state has a simple linear dependence P = a(sqrt{s})*e, where a = c_s**2 is the sound velocity squared. It varies from 0.12 \pm 0.01 at E_{lab} = 11.6 AGeV to 0.145 \pm 0.005 at E_{lab} = 160 AGeV. Change of the slope in a(sqrt{s}) behavior occurs at E_{lab} = 40 AGeV and can be assigned to the transition from baryon-rich to meson-dominated matter. The phase diagrams in the T - mu_B plane show the presence of kinks along the lines of constant entropy per baryon. These kinks are linked to the inelastic (i.e. chemical) freeze-out in the system.
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