Aspects of the momentum dependence of the equation of state and of the residual NN cross section, and their effects on nuclear stopping
Résumé
With the semiclassical Landau-Vlasov transport model we studied the stopping observable RE, the energy-based isotropy ratio, for the Xe129+Sn120 reaction at beam energies spanning 12A to 100A MeV. We investigated the impacts of the nonlocality of the nuclear mean field, of the in-medium modified nucleon-nucleon (NN) cross section, and of the reaction centrality. A fixed set of model parameters yields RE values that favorably compare with the experimental ones, but only for energies below the Fermi energy EF. Above EF agreement is readily possible, but by a smooth evolution with energy of the parameter that controls the in-medium modification of NN cross section. By comparing the simulation correction factor F applied to the free NN cross section with the one deduced from experimental data [Phys. Rev. C 90, 064602 (2014)PRVCAN0556-281310.1103/PhysRevC.90.064602], we infer that the zero-range mean field almost entirely reproduces it. Also, in accordance with what has been deduced from experimental data, around EF a strong reduction of the free NN cross section is found. In order to test the impact of sampling central collisions by multiplicity, an event generator (hipse) was used. We obtain that high multiplicity events are spread over a broad impact parameter range, but it turns out that this has a small effect on the observable RE and, thus, on F as well.