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arXiv · 1701.06682

Medium effects on pion production in heavy ion collisions

Zhen Zhang·Che Ming Ko
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Abstract

Within the framework of the relativistic Vlasov-Uehling-Uhlenbeck transport model based on the relativistic nonlinear NL$ρ$ interaction, we study pion in-medium effects on the $π^-/π^+$ ratio in Au+Au collisions at the energy of $E/A=400~\mathrm{MeV}$. 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 the $π^-/π^+$ 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 suppressed $π^-/π^+$ ratio. Including also the in-medium threshold effects on $Δ$ resonance production and decay and using a nuclear symmetry energy with a slope parameter $L=59~\mathrm{MeV}$ by reducing the coupling of isovector-vector $ρ$ meson to nucleon, our result is in good agreement with measured $π^-/π^+$ 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.

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Zhen Zhang, Che Ming Ko. 2017-01-23. Medium effects on pion production in heavy ion collisions. https://doi.org/10.1103/physrevc.95.064604

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