Energy dependence of pion in-medium effects on \pi^-/\pi^+ ratio in heavy-ion collisions

TL;DR

This study investigates how pion in-medium effects influence the /+ ratio in heavy-ion collisions, revealing that these effects decrease the ratio more significantly at lower energies due to spectral function narrowing.

Contribution

It introduces a thermal model combined with IBUU transport results to analyze pion in-medium effects on charged-pion ratios across different collision energies.

Findings

Pion in-medium effects decrease the /+ ratio.

The effect is more pronounced at lower collision energies.

Pion spectral functions narrow at lower temperatures.

Abstract

Within the framework of a thermal model with its parameters fitted to the results from an isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model, we study the pion in-medium effect on the charged-pion ratio in heavy-ion collisions at various energies. We find that due to the cancellation between the effects from pion-nucleon s-wave and p-wave interactions in nuclear medium, the \pi^-/\pi^+ ratio generally decreases after including the pion in-medium effect. The effect is larger at lower collision energies as a result of narrower pion spectral functions at lower temperatures.