Speaker
Description
Based on the microscopic Brueckner–Hartree–Fock (BHF) approach, we systematically investigate the medium modifications of nucleon–nucleon (NN) scattering cross sections and their applications in transport simulations of heavy-ion collisions. By accurately treating the total momentum K of the colliding nucleon pair, the in-medium NN cross sections are calculated at different densities and isospin asymmetries. Furthermore, analytical parameterizations of the medium correction factors are provided for convenient implementation in transport models.
The microscopic in-medium cross sections are subsequently incorporated into the IBUU transport model to investigate the effects of medium modifications on various observables, including the collective flows of emitted nucleons, nuclear stopping, neutron-to-proton ratio, neutron–proton differential flow, pion multiplicities, and the π−/π+ ratio. In addition, the individual contributions from the scattering amplitude, density of states, and total momentum K dependence are separately explored.
The results demonstrate that among the different medium effects, the reduction of the cross section induced by the effective mass plays a dominant role, while the modification of the scattering amplitude arising from the in-medium G-matrix provides a relatively minor contribution and tends to enhance the cross sections. The effect of the total momentum K dependence is also found to be non-negligible. The neutron-to-proton ratio and neutron–proton transverse flow difference exhibit weak sensitivity to the in-medium cross sections, making them suitable observables for probing the symmetry energy. In contrast, the neutron–proton differential flow and pion production observables show strong sensitivity to the medium modifications.
Therefore, considering only the effective mass correction is insufficient, and a complete treatment of medium effects, including contributions from the scattering amplitude and the total momentum K dependence, is essential for reliable applications of in-medium NN cross sections in transport models.
