In-medium nucleon-nucleon cross section in nuclear matter

Abstract

In-medium nucleon-nucleon ($NN$) cross sections at various densities and isospin asymmetries are investigated systematically in the framework of the Brueckner-Hartree-Fock approach. The calculations are base on the exact treatment of the center-of-mass momentum instead of the total momentum approximation employed in previous works. The neutron-proton in-medium cross section is shown to exhibit nearly isospin asymmetry independence. For convenience in application, analytical formulas embodying the medium correction to free $NN$ cross section with parameters calibrated to the calculated results have been provided. Using these formulas, the transverse and elliptic flows of emitted nucleons in heavy-ion collisions are studied within the isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model. We find the medium effect of the cross section from the $G$ matrix contributes to the transverse and elliptic flows oppositely to and obviously smaller than that from the effective mass. In addition, the present microscopic in-medium cross sections can significantly revise the predictions of the transverse and elliptic flows compared to the in-medium cross sections previously adopted in transport models for heavy-ion collisions.