In-medium Nucleon-nucleon Scattering Cross Sections And The Relevant Effects On The Observables In Nuclear Reaction

We have calculated in-medium nucleon-nucleon（NN）cross sections based on the microscopic many-body Brueckner-Hartree-Fock（BHF）method with bare two-body in-teractionAV（18）potential and microscopic three-body forces.The calculations are based on exact numerical treatment of the total momentum of the two scattering nucleons instead of the average total momentum approximation employed in previous works.The three-body force effects and medium effects on the in-mediumNNcross sections are discussed.For convenience in application,parametric analytical formulas of the medium reduction factors are provided.In-mediumNNcross sections are related to the state of the scattering two nucleons and depend complicatedly on the total nucleon density and isospin asymmetry of nuclear medium,as well as the total momentum and the total kinetic energy of the two scattering nucleons due to the influence of the surrounding nucleons.To facilitate applications,deep neural network method is adopted to obtainNNscross sections under various conditions based on the microscopic predicted in-mediumNNcross sections.ConsideringNNcross sections is a fundamental input to the transport models of heavy ion collisions,we investigate the transverse flow and elliptic flow of protons and neutrons in heavy ion collisions by using five different kinds ofNNcross sections,including the vacuum cross sectionσ_freeand the in-medium effective cross sectionsσ_BHF,σ_BHF^*,σ_effandσ_fit.The transverse flow and elliptic flow are sensitive probes for detecting the softness and hardness of the equation of state of nuclear matter,so it is of great significance to study the influence of theNNcross sections on transverse flow and elliptic flow.It is shown that the medium effect of theNNcross sections on transverse flow and elliptic flow mainly comes from the effective mass.While the influence of the medium effect from thematrix is quite smaller.