Comparison of heavy-ion transport simulations: Collision integral in a box

Ying Xun Zhang, Yong Jia Wang, Maria Colonna, Pawel Danielewicz, Akira Ono, Manyee Betty Tsang, Hermann Wolter, Jun Xu, Lie Wen Chen, Dan Cozma, Zhao Qing Feng, Subal Das Gupta, Natsumi Ikeno, Che Ming Ko, Bao An Li, Qing Feng Li, Zhu Xia Li, Swagata Mallik, Yasushi Nara, Tatsuhiko OgawaAkira Ohnishi, Dmytro Oliinychenko, Massimo Papa, Hannah Petersen, Jun Su, Taesoo Song, Janus Weil, Ning Wang, Feng Shou Zhang, Zhen Zhang

Research output: Contribution to journalArticlepeer-review

82 Citations (Scopus)

Abstract

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 orderto 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.

Original languageEnglish
Article number034625
JournalPhysical Review C
Volume97
Issue number3
DOIs
Publication statusPublished - 2018 Mar 30

ASJC Scopus subject areas

  • Nuclear and High Energy Physics

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