Collisional relaxation in simulations of heavy-ion collisions using Boltzmann-type equations

We compare three test-particle methods currently used in numerical simulations of Boltzmann-type equations for the analysis of intermediate-energy heavy-ion collisions with an exact solution of the Krook-Wu model. These methods are the full ensemble, parallel ensemble, and hybrid techniques. We find that collisional relaxation is sensitive to the method of simulation used. The full ensemble approach is found to agree with the exact results of the Krook-Wu model. The parallel ensemble procedure provides a reasonable approximation to the analytical relaxation rate for a wide range of systems, while the hybrid method overestimates the relaxation rate. We further compare transverse flow data from the first two of these methods in a cascade simulation of heavy-ion collisions, and find reasonable agreement provided the two-body cross section is not enhanced by a large factor over its free space value. This has implications for quantitative comparisons of calculations to experimental data