Comparison of Heavy-Ion Transport Simulations: Mean-field Dynamics in a Box

TL;DR

This study compares different heavy-ion transport simulation codes in a controlled box environment, analyzing their mean-field response and zero-sound propagation, highlighting differences between BUU-like and QMD-like methods.

Contribution

The paper provides a systematic comparison of BUU-like and QMD-like transport codes for zero-sound propagation in a periodic box, identifying key differences and improvements.

Findings

BUU-like codes accurately reproduce analytical zero-sound features with proper parameters.

QMD-like codes exhibit larger damping and slower oscillations due to phase-space fluctuations.

Recent lattice formulations improve QMD-like code performance.

Abstract

Within the transport model evaluation project (TMEP) of simulations for heavy-ion collisions, the mean-field response is examined here. Specifically, zero-sound propagation is considered for neutron-proton symmetric matter enclosed in a periodic box, at zero temperature and around normal density. The results of several transport codes belonging to two families (BUU-like and QMD-like) are compared among each other and to exact calculations. For BUU-like codes, employing the test particle method, the results depend on the combination of the number of test particles and the spread of the profile functions that weight integration over space. These parameters can be properly adapted to give a good reproduction of the analytical zero-sound features. QMD-like codes, using molecular dynamics methods, are characterized by large damping effects, attributable to the fluctuations inherent in their phase-space representation. Moreover, for a given nuclear effective interaction, they generally lead to slower density oscillations, as compared to BUU-like codes. The latter problem is mitigated in the more recent lattice formulation of some of the QMD codes. The significance of these results for the description of real heavy-ion collisions is discussed.