Isospin-dependent pion in-medium effects on charged pion ratio in heavy ion collisions

TL;DR

This paper investigates how isospin-dependent in-medium effects influence the charged pion ratio in heavy ion collisions, using theoretical models to evaluate pion spectral functions in asymmetric nuclear matter and discussing implications for nuclear symmetry energy.

Contribution

It introduces a combined theoretical approach using chiral perturbation theory and delta-resonance models to evaluate pion spectral functions in asymmetric nuclear matter, highlighting isospin effects.

Findings

Positively charged pion spectral strength is larger at low energies in neutron-rich matter.

The isospin-dependent effects slightly decrease the negatively to positively charged pion ratio.

Results have implications for extracting nuclear symmetry energy from experimental data.

Abstract

Using results from the chiral perturbation theory for the s-wave interaction and the delta-resonance model for the p-wave interaction of pions with nucleons, we have evaluated the spectral functions of pions in asymmetric nuclear matter with unequal proton and neutron densities. We find that in hot dense neutron-rich matter the strength of the spectral function of positively charged pion at low energies is somewhat larger than that of negatively charged pion. In a thermal model, this isospin-dependent effect slightly reduces the ratio of negatively charged to positively charged pions that are produced in heavy ion collisions induced by radioactive beams. Relevance of our results to the determination of the nuclear symmetry energy from measured ratio of negatively to positively charged pions produced in heavy ion collisions is discussed.