利用两π介子HBT关联约束重离子碰撞中高密核物质的状态方程

The High-density Equation of State in Heavy-ion Collisions:Constraints from Two-pion HBT Correlation

高重子密度区核物质状态方程的研究是当前核物理研究的前沿热点问题之一。利用极端相对论量子分子动力学(UrQMD)模型,以两π介子Hanbury-Brown-Twiss(HBT)关联为例讨论了2~5倍饱和密度(ρ_(0))区核物质状态方程对两粒子关联效应的影响。通过使用不同的核物质状态方程,展示了密度依赖的势相互作用以及相变对两π介子HBT关联和π介子发射源时空属性的影响。结果显示,在~5ρ_(0)以下,π介子发射源的HBT半径及参数敏感于核物质状态方程的软硬,通过与实验数据的比较,现有的HBT半径实验数据排除了~4ρ_(0)以下发生一阶相变的可能性,并支持一个在低密区(-4ρ_(0))表现偏硬,且在高密区由于相变而逐渐软化的核物质状态方程。研究结果强调了π介子发射源的HBT半径及参数敏感于核物质状态方程的软硬,可用于理解和约束高重子密度区的核物质状态方程。

The investigation of the equation of state(EoS)of nuclear matter,especially at high baryon densities is one of the hot topics in the frontier of nuclear physics.The impact of the EoS at 2~5 times saturation density ρ_(0) on the two-particle correlation is discussed with the ultra-relativistic quantum molecular dynamics(UrQMD)model.Focusing on the two Hanbury-Brown-Twiss(HBT)correlations,by adopting different EoSs,the effects of potential interaction and phase transition on the HBT correlation and the spatiotemporal properties of the emission source of π are investigated.The results show that below~5ρ_(0),the HBT radius and parameters are sensitive to the stiffness of the EoS.By comparing with the experiment data,firstorder phase transition with a significant softening of the equation of state below 4 times nuclear saturation density can be excluded using HBT data,and the available data on the HBT radi in the investigated energy region favor a relatively stiff EoS at low densities,which then turns into a soft EoS at high densities.These results highlight that the pion's HBT radius and parameters are sensitive to the stiffness of the equation of state,and can be used to constrain and understand the equation of state in the high baryon density region.