Comparison of heavy-ion transport simulations: Collision integral in a box
Comparison of heavy-ion transport simulations: Collision integral in a box
复制标题
重离子输运模拟的比较：盒子中的碰撞积分
DOI：
10.1103/physrevc.97.034625
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发表时间：
2018
影响因子：
3.1
通讯作者：
O
中科院分区：
文献类型：
--
作者：
Zhang Ying-Xun;Wang Yong-Jia;Colonna Maria;Danielewicz Pawel;Ono Akira;Tsang Manyee Betty;Wolter Hermann;Xu Jun;Chen Lie-Wen;Cozma Dan;Feng Zhao-Qing;Das Gupta Subal;Ikeno Natsumi;Ko Che-Ming;Li Bao-An;Li Qing-Feng;Li Zhu-Xia;Mallik Swagata;Nara Yasushi;O
传输代码的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。为了了解不同广泛使用的输运代码之间差异的根源，我们比较了15个这样的代码，这些代码被限制在一个具有周期边界的系统的受控条件下，在饱和密度和温度为0或5 MeV的情况下用费米-狄拉克分布初始化。在这样的计算中，人们能够分别检查运输代码的不同组成部分。在代码评估项目的第二次发布中，我们只考虑两体碰撞项；即，我们执行级联计算。当人为地抑制Pauli阻塞时，发现对于大多数代码的冲突率与基本级联码的分析结果或完全受控的结果一致(在1%或更好)。为了实现这一目标，有必要消除同一对碰撞粒子之间的相关性，这种相关性取决于所采用的碰撞配方。在具有主动泡利阻塞的计算中，发现阻塞概率偏离了预期参考值。其原因在于相空间的大量起伏和拖尾与相空间表示中的数值算法和模型假设有关。这导致了大多数传输代码中的阻塞概率的降低，从而模拟的系统逐渐从费米-狄拉克向玻尔兹曼分布演化。由于Boltzmann-Uehling-Uhlenbeck程序中的数值涨落较弱，费米-狄拉克统计量在那里保持的时间比量子分子动力学程序中的更长。作为这项调查的结果，我们能够判断在运输模拟中确定碰撞概率和泡利阻塞的最有效策略。输运计算中其他成分的类似研究，如平均场传播或核子共振和介子的产生，将在未来的出版物中讨论。
Simulations by transport codes are indispensable to extract valuable physical information from heavy-ion collisions. In order to understand the origins of discrepancies among different widely used transport codes, we compare 15 such codes under controlled conditions of a system confined to a box with periodic boundary, initialized with Fermi-Dirac distributions at saturation density and temperatures of either 0 or 5 MeV. In such calculations, one is able to check separately the different ingredients of a transport code. In this second publication of the code evaluation project, we only consider the two-body collision term;i.e., we perform cascade calculations. When the Pauli blocking is artificially suppressed, the collision rates are found to be consistent for most codes (to within 1% or better) with analytical results, or completely controlled results of a basic cascade code. In order to reach that goal, it was necessary to eliminate correlations within the same pair of colliding particles that can be present depending on the adopted collision prescription. In calculations with active Pauli blocking, the blocking probability was found to deviate from the expected reference values. The reason is found in substantial phase-space fluctuations and smearing tied to numerical algorithms and model assumptions in the representation of phase space. This results in the reduction of the blocking probability in most transport codes, so that the simulated system gradually evolves away from the Fermi-Dirac toward a Boltzmann distribution. Since the numerical fluctuations are weaker in the Boltzmann-Uehling-Uhlenbeck codes, the Fermi-Dirac statistics is maintained there for a longer time than in the quantum molecular dynamics codes. As a result of this investigation, we are able to make judgements about the most effective strategies in transport simulations for determining the collision probabilities and the Pauli blocking. Investigation in a similar vein of other ingredients in transport calculations, like the mean-field propagation or the production of nucleon resonances and mesons, will be discussed in the future publications.