Feasibility of constraining the curvature parameter of the symmetry energy using elliptic flow data
Feasibility of constraining the curvature parameter of the symmetry energy using elliptic flow data
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DOI：
10.1140/epja/i2018-12470-1
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发表时间：
2018-03-09
影响因子：
2.7
通讯作者：
Cozma, M. D.
中科院分区：
文献类型：
--
作者：
Cozma, M. D.
一种QMD输运模型，其采用修正的动量相关相互作用（MDI 2）势，补充了一个与FOPI实验的自由核子和轻团簇多重数相空间聚结模型，通过与FOPI-LAND和ASYEOS合作组在Au-197 + Au-197中测量的实验椭圆流比的比较，研究了饱和点以上对称能的密度依赖性。400 MeV/核子碰撞能量下的197次碰撞。先前使用相同模型的计算已经证明，中子-质子和中子-带电粒子椭圆流比探测平均不同密度，原则上允许提取对称能的斜率L和曲率K-sym参数。为了利用这一结果的Gogny相互作用启发的潜力被修改的密度依赖，动量独立的条款，同时执行一个密切的描述的经验核子光学势，允许独立的修改L和K对称。通过对中子-质子和中子-带电粒子椭圆流比的理论预测与实验数据进行比较，得到了以下约束：L = 85 +/- 22（exp）+/- 20（th）+/- 12（sys）MeV，K-sym = 96 +/- 315（exp）+/- 170（th）+/- 166（sys）MeV。理论误差包括由于在状态方程的isoscope部分的不确定性的影响，等值矢量中子-质子有效质量分裂的值，在介质中的弹性核子-核子截面的影响，泡利阻塞算法的变体和考虑的系统的总能量守恒的情况。系统的不确定性所产生的传输模型无法重现实验轻集群质子的多重性比。一个没有系统理论不确定性的L值可以单独从中子-质子椭圆流比中提取：L = 84 +/- 30（exp）+/- 19（th）MeV。它表明，椭圆流比达到最大的灵敏度在重离子碰撞的K-对称参数约250兆电子伏/核子碰撞能量，允许减少其实验组件的不确定性约150兆电子伏。
A QMD transport model that employs a modified momentum dependent interaction (MDI2) potential, supplemented by a phase-space coalescence model fitted to FOPI experimental multiplicities of free nucleons and light clusters is used to study the density dependence of the symmetry energy above the saturation point by a comparison with experimental elliptic flow ratios measured by the FOPI-LAND and ASYEOS Collaborations in Au-197 + Au-197 collisions at 400 MeV/nucleon impact energy. A previous calculation using the same model has proven that neutron-to-proton and neutron-to-charged-particles elliptic flow ratios probe on average different densities allowing in principle the extraction of both the slope L and curvature K-sym parameters of the symmetry energy. To make use of this result a Gogny interaction inspired potential is modified by the addition of a density dependent, momentum independent term, while enforcing a close description of the empirical nucleon optical potential, allowing independent modifications of L and K-sym. Comparing theoretical predictions with experimental data for neutron-to-proton and neutron-to-charged-particles elliptic flow ratios the following constraint is extracted: L = 85 +/- 22(exp) +/- 20(th) +/- 12(sys) MeV and K-sym = 96 +/- 315(exp) +/- 170(th) +/- 166(sys) MeV. Theoretical errors include effects due to uncertainties in the isoscalar part of the equation of state, value of the isovector neutron-proton effective mass splitting, in-medium effects on the elastic nucleon-nucleon cross-sections, Pauli blocking algorithm variants and scenario considered for the conservation of the total energy of the system. Systematical uncertainties are generated by the inability of the transport model to reproduce experimental light-cluster-to-proton multiplicity ratios. A value for L free of systematical theoretical uncertainties can be extracted from the neutron-to-proton elliptic flow ratio alone: L = 84 +/- 30(exp) +/- 19(th) MeV. It is demonstrated that elliptic flow ratios reach a maximum sensitivity on the K-sym parameter in heavy-ion collisions of about 250 MeV/nucleon impact energy, allowing a reduction of its experimental component of uncertainty to about 150 MeV.