Probing The In-medium Nucleon-nucleon Inelastic Scattering Cross Section And Thermal Equilibrium In Heavy-ion Collisions

The paper contains two parts:(1)Probing the in-medium nucleon-nucleon inelastic scattering cross section by using an energy-dependent n/p ratio;(2)Probing the thermal equilibrium of heavy ion collisions by n/p ratio.Symmetry energy terms is one of the most important part of the equation of state(EOS)of asymmetric nuclear matter.It plays an important role in nuclear physics and astrophysics,for example,neutron star merging,supernova explosion,and the synthesis of superheavy nuclei(SHN).The~-?~+ratio and neutron-to-proton ratio n/p were found to be sensitive to symmetry energy.However,the~-?~+ratio is also influenced by the in-medium nucleon-nucleon(NN)cross section in the intermediate energy heavy ion collisions(HIC).If a probe can be used to constrain the inelastic nucleon-nucleon cross scattering in medium,symmetry energy can be better studied in the future,and a more accurate equation of state asymmetric nuclear matter can be obtained,so that the properties of neutron stars can be better understood.Based on the isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model,in-medium nucleon-nucleon inelastic scattering(which is dominated by pion production at low and intermediate energies)is explored.It is found that the in-medium modification of nucleon-nucleon inelastic scatterings appear to reduce the neutron-to-proton ratio n/p at higher kinetic energies.Although the in-medium modification of nucleon-nucleon inelastic scatterings,as expected,affects the value of~-?~+ratio,considering a series of undetermined properties of delta resonance and?in medium,the energetic neutron-to-proton ratio n/p is more suitable to be used to probe the in-medium correction of nucleon-nucleon inelastic scatterings.The second work of this paper is to find the probe for the thermal equilibrium of heavy ion collisions by using two forms of mean field potential in the BUU program.The two forms of mean field potential are the mean field potential originally used in the BUU code,and the other is the stationary state of mean field potential.By comparing the results with two different potentials,it is found that the neutron-to-proton n/p ratio can be used as a probe of thermal equilibrium of heavy-ion collisions.