Within the framework of the relativistic Vlasov-Uehling-Uhlenbeck transport model based on the relativistic nonlinear NLρ interaction, we study pion in-medium effects on the π−/π+ ratio in Au+Au collisions at the energy of E/A = 400 MeV. 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 Δ-hole model, respectively. We find that theπ−/π+ 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 suppressedπ−/π+ ratio. Including also the in-medium threshold effects onΔresonance production and decay and using a nuclear symmetry energy with a slope parameter L = 59 MeV by reducing the coupling of isovector-vector ρ meson to nucleon, our result is in good agreement with measuredπ−/π+ 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.

Host: Prof. Lie-Wen Chen