Medium effects on pion production in heavy ion collisions
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2017 American Physical Society. Within the framework of the relativistic Vlasov-Uehling-Uhlenbeck transport model based on the relativistic nonlinear NL interaction, we study pion in-medium effects on the -/+ ratio in Au+Au collisions at the energy of E/A=400MeV. These effects include the isospin-dependent pion s-wave and p-wave potentials, which are taken from calculations based on the chiral perturbation theory and the -hole model, respectively. We find that the -/+ ratio in this collision is suppressed by the pion s-wave potential but enhanced by the p-wave potential, with a net effect of a significantly suppressed -/+ ratio. Including also the in-medium threshold effects on resonance production and decay and using a nuclear symmetry energy with a slope parameter L=59MeV by reducing the coupling of isovector-vector meson to nucleon, our result is in good agreement with measured -/+ ratio from the FOPI Collaboration. We further investigate the pion in-medium effects on the ratio of charged pions as a function of their kinetic energies.