Comparison of heavy-ion transport simulations: Collision integral with pions and Delta resonances in a box
Comparison of heavy-ion transport simulations: Collision integral with pions and Delta resonances in a box
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重离子输运模拟的比较：盒子中π介子和Delta共振的碰撞积分
DOI：
10.1103/physrevc.100.044617
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发表时间：
2019
影响因子：
3.1
通讯作者：
Ohnishi Aki
中科院分区：
文献类型：
--
作者：
Ono Akira;Xu Jun;Colonna Maria;Danielewicz Pawel;Ko Che Ming;Tsang Manyee Betty;Wang Yong-Jia;Wolter Hermann;Zhang Ying-Xun;Chen Lie-Wen;Cozma Dan;Elfner Hannah;Feng Zhao-Qing;Ikeno Natsumi;Li Bao-An;Mallik Swagata;Nara Yasushi;Ogawa Tatsuhiko;Ohnishi Aki
背景：通过传输代码进行模拟对于从重离子碰撞中提取有价值的物理信息是必不可少的。目的：评估、理解和减少输运代码结果中的不确定性，这些不确定因素源于在处理共振和点的产生时采用不同的近似。方法：我们比较了10个输运代码在受控条件下的比较，这些系统被限制在一个盒子中，具有周期边界条件，以饱和密度和60 MeV的核子初始化。在目前的比较中，反应和实现了，但泡利阻塞和平均场势失活了。因此，这些是包括介子和共振在内的级联计算。将结果与化学平衡的理想气体混合物和速率方程的两个参考算例的结果进行了比较。结果：对于AND的个数，在许多程序中观察到与参考值的偏差，并且它们显著地依赖于时间步长的大小。这些偏差与同一时间步长内发生的碰撞和衰变等反应顺序的不同方式有关。在反应速率和同位旋物种之间的数目比上，与参考值有较好的一致性。然而，反应速率和数比都受到粒子位置之间的关联的影响，这种关联在Boltzmann方程中是不存在的，但在许多输运计算中是由处理粒子散射的方式引起的。在让存在共振衰变后，输运代码预测的不确定度对于初始系统来说是在几个百分点以内。结论：在这个简化的情况下，粒子在盒子中的最终比的不确定度足够小，因此它不会强烈地影响来自重离子碰撞的高密度对称能量的约束。大多数不确定性的来源已经被理解，个别代码在未来的应用中可能会得到进一步的改进。这项调查将在未来扩展到重离子碰撞，以确保这里发现的问题仍在控制之下。
Background:Simulations by transport codes are indispensable for extracting valuable physical information from heavy-ion collisions. Pion observables such as theyield ratio are expected to be sensitive to the symmetry energy at high densities.Purpose:To evaluate, understand, and reduce the uncertainties in transport-code results originating from different approximations in handling the production ofresonances and pions.Methods:We compare ten transport codes under controlled conditions for a system confined in a box, with periodic boundary conditions, and initialized with nucleons at saturation density and at a temperature of 60 MeV. The reactionsandare implemented, but the Pauli blocking and the mean-field potential are deactivated in the present comparison. Thus, these are cascade calculations including pions andresonances. Results are compared to those from the two reference cases of a chemically equilibrated ideal gas mixture and of the rate equation.Results:For the numbers ofand, deviations from the reference values are observed in many codes, and they depend significantly on the size of the time step. These deviations are tied to different ways in ordering the sequence of reactions, such as collisions and decays, that take place in the same time step. Better agreements with the reference values are seen in the reaction rates and the number ratios among the isospin species ofand. Both the reaction rates and the number ratios are, however, affected by the correlations between particle positions, which are absent in the Boltzmann equation, but are induced by the way particle scatterings are treated in many of the transport calculations. The uncertainty in the transport-code predictions of theratio, after letting the existingresonances decay, is found to be within a few percent for the system initialized at.Conclusions:The uncertainty in the finalratio in this simplified case of particles in a box is sufficiently small so that it does not strongly impact constraining the high-density symmetry energy from heavy-ion collisions. Most of the sources of uncertainties have been understood, and individual codes may be further improved in future applications. This investigation will be extended in the future to heavy-ion collisions to ensure the problems identified here remain under control.