同位旋分馏、同位旋弛豫与非对称核物质状态方程

采用同位旋相关的输运模型IBUU04对中能区(400 MeV/u～1GeV/u)重离子碰撞中产生的π-/π+产额比实验数据进行了系统分析.通过符合π-/π+的激发函数及其随系统N/Z比变化关系的实验数据发现,对称能在约2ρ0的区域具有随密度的增加而减小的趋势.通过选择具有相同N/Z但不同质量的碰撞系统,研究了π-/π+对Esym(ρ)的依赖敏感度随系统大小和入射能量的关系,发现该敏感度与同位旋分馏程度有直接的关联.此外,π-/π+在同位旋非对称系统(Ru+Zr与Zr+Ru)中的分布表明中心碰撞的同位旋没有达到完全平衡,其分布特征与核子分布特征具有明显的差异,这可能支持π-/π+是高密区Esym(ρ)探针的一个证据.

Isospin fractionation, isospin relaxation and asymmetric nuclear equation of state

The experimental π-/π＋ ratios in the heavy ion collisions at intermediate energies （400 MeV/u ～ 1 GeV/u） are reanalyzed systematically by applying the isospin dependent transport model IBUU04. By fitting the excitation function and the system dependence of π-/π＋ ratio, it is found that the symmetry tends to soften with the densities at about 2ρ0 . The π-/π ＋ ratios are calculated as functions of system size and incident energy in three systems with the same N/Z but different masses. It is shown that the sensitivity of π-/π＋ depending on E sym （ρ） correlates with the degree of isospin fractionation. In addition, the rapidity distribution of π-/π＋ in an isospin asymmetric systems （Ru＋Zr and Zr＋Ru） shows that the equilibrium of isospin degree of freedom is not fully achieved. The difference with the behavior of protons suggests that π-/π＋ probes the nuclear matter at high density region.