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arXiv 2301.03066nucl-thnucl-ex
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动量相关相互作用、对称能和近阈值$NN\to NΔ$截面对同位旋敏感流和π介子观测值的影响

Impacts of momentum dependent interaction, symmetry energy and near-threshold $NN\to NΔ$ cross sections on isospin sensitive flow and pion observables

Yangyang Liu, Yingxun Zhang, Junping Yang, Yongjia Wang, Qingfeng Li, Zhuxia Li

备注：
9 pages, 7 figures. arXiv admin note: text overlap with arXiv:2301.00212
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摘要：

基于超相对论量子分子动力学（UrQMD）模型，研究了动量相关相互作用、对称能和近阈值$NN\to NΔ$截面对同位旋敏感集体流和π介子观测值的影响.我们的结果证实了中子和带电粒子的椭圆流，即$v_2^n$和$v_2^{ch}$，对动量依赖相互作用的强度和椭圆流比，即，$v_2^n/v_2^{ch}$，对刚度对称能敏感。为了描述阈能附近的π介子多重性，精确的$NN\to NΔ$截面是至关重要的。通过对UrQMD模型中动量相关相互作用和$NN\to NΔ$截面的修正，可以用对称能斜率为5 ~ 70 MeV的参数集较好地描述中子和带电粒子的定向流和椭圆流、中子与带电粒子的椭圆流比、带电π介子多重数及其比值$π^-/π^+$等7个观测量.为了描述在集体流和π介子观测量所探测的密度下对称能的约束，研究并使用了命名的特征密度。我们的分析发现，流的特征密度约为1.2 $ρ_0$，π介子的特征密度约为1.5 $ρ_0$，并得到了对称能在特征密度为$S(1.2ρ_0)=34\pm 4$ MeV和$S(1.5ρ_0)=36\pm 8$ MeV时的约束。这些结果与前人用不同输运模型的π介子和流观测量分析的结果一致，表明在同位旋敏感观测量的特征密度下，对称性能量约束应得到合理的描述.

英文摘要：

Based on the ultra-relativistic quantum molecular dynamics (UrQMD) model, the impacts of momentum dependent interaction, symmetry energy and near-threshold $NN\to NΔ$ cross sections on isospin sensitive collective flow and pion observables are investigated. Our results confirm that the elliptic flow of neutrons and charged particles, i.e. $v_2^n$ and $v_2^{ch}$, are sensitive to the strength of momentum dependence interaction and the elliptic flow ratio, i.e., $v_2^n/v_2^{ch}$, is sensitive to the stiffness of symmetry energy. For describing the pion multiplicity near the threshold energy, accurate $NN\to NΔ$ cross sections are crucial. With the updated momentum dependent interaction and $NN\to NΔ$ cross sections in UrQMD model, seven observables, such as directed flow and elliptic flow of neutrons and charged particles, the elliptic flow ratio of neutrons to charged particles, charged pion multiplicity and its ratio $π^-/π^+$, can be well described by the parameter sets with the slope of symmetry energy from 5 MeV to 70 MeV. To describe the constraints of symmetry energy at the densities probed by the collective flow and pion observables, the named characteristic density is investigated and used. Our analysis found that the flow characteristic density is around 1.2$ρ_0$ and pion characteristic density is around 1.5$ρ_0$, and we got the constrains of symmetry energy at characteristic densities are $S(1.2ρ_0)=34\pm 4$ MeV and $S(1.5ρ_0)=36\pm 8$ MeV. These results are consistent with previous analysis by using pion and flow observable with different transport models, and demonstrate a reasonable description of symmetry energy constraint should be presented at the characteristic density of isospin sensitive observables.

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