Report/Journal Article

GSI-2020-00007

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Comparison of heavy-ion transport simulations: Collision integral with pions and Δ resonances in a box

Ono, A. (Corresponding author) ; Xu, J. ; Colonna, M. ; Danielewicz, P. ; Ko, C. M. ; Tsang, M. B. ; Wang, Y.-J. ; Wolter, H. ; Zhang, Y.-X. ; Chen, L.-W. ; Cozma, D. ; Elfner, H.GSI* ; Feng, Z.-Q. ; Ikeno, N. ; Li, B.-A. ; Mallik, S. ; Nara, Y. ; Ogawa, T. ; Ohnishi, A. ; Oliinychenko, D. ; Su, J. ; Song, T.GSI* ; Zhang, F.-S. ; Zhang, Z.

2019
Inst. Woodbury, NY

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Please use a persistent id in citations: doi:10.1103/PhysRevC.100.044617

Report No.: arXiv:1904.02888

Abstract: We compare ten transport codes for a system confined in a box, aiming at improved handling of the production of $\Delta$ resonances and pions, which is indispensable for constraining high-density symmetry energy from observables such as the $\pi^-/\pi^+$ yield ratio in heavy-ion collisions. The system in a box is initialized with nucleons at saturation density and at 60 MeV temperature. The reactions $NN\leftrightarrow N\Delta$ and $\Delta\leftrightarrow N\pi$ are implemented, but the Pauli blocking and the mean-field potential are deactivated in the present comparison. Results are compared to those from the two reference cases of a chemically equilibrated ideal gas mixture and of the rate equation. In the results of the numbers of $\Delta$ and $\pi$, 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 collisions and decays, that take place in the same time step. Better agreements are seen in the reaction rates and the number ratios among the isospin species of $\Delta$ and $\pi$. These are, however, affected by the correlations, which are absent in the Boltzmann equation, but are induced by the way particle scatterings are treated in transport calculations. The uncertainty in the transport-code predictions of the $\pi^-/\pi^+$ ratio for the system initialized at n/p = 1.5, after letting the existing $\Delta$ resonances decay, is found to be within a few percent, which 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. This investigation will be extended in the future to heavy-ion collisions to ensure the problems identified here remain under control.

Note: 36 pages, 27 figures; a new Fig. 21 and revised results from some codes, achieving improved and consistent understanding

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Contributing Institute(s):

1. HIC for FAIR - Helmholtz International Center for FAIR - Data Analysis, Theory and Simulations (HIC4FAIR)

Research Program(s):

1. 612 - Cosmic Matter in the Laboratory (POF3-612) (POF3-612)

Appears in the scientific report 2019

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Database coverage:
; Clarivate Analytics Master Journal List ; Current Contents - Physical, Chemical and Earth Sciences ; Ebsco Academic Search ; IF < 5 ; JCR ; SCOPUS ; Science Citation Index ; Science Citation Index Expanded ; Web of Science Core Collection

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