Medium effects on charged pion ratio in heavy ion collisions

TL;DR

This paper investigates how pion charge ratios in heavy ion collisions are affected by medium interactions, highlighting the importance of both p-wave and s-wave effects in understanding nuclear symmetry energy.

Contribution

It provides a comparative analysis of p-wave and s-wave interactions on pion ratios, emphasizing their impact on extracting nuclear symmetry energy from experimental data.

Findings

P-wave interactions increase the ^-/^+ ratio in neutron-rich matter.

S-wave interactions slightly reduce the ^-/^+ ratio.

The effect size is comparable to uncertainties in nuclear symmetry energy predictions.

Abstract

We have recently studied in the delta-resonance--nucleon-hole model the dependence of the pion spectral function in hot dense asymmetric nuclear matter on the charge of the pion due to the pion p-wave interaction in nuclear medium. In a thermal model, this isospin-dependent effect enhances the ratio of negatively charged to positively charged pions in neutron-rich nuclear matter, and the effect is comparable to that due to the uncertainties in the theoretically predicted stiffness of nuclear symmetry energy at high densities. This effect is, however, reversed if we also take into account the s-wave interaction of the pion in nuclear medium as given by chiral perturbation theory, resulting instead in a slightly reduced ratio of negatively charged to positively charged pions. Relevance of our results to the determination of the nuclear symmetry energy from the ratio of negatively to positively charged pions produced in heavy ion collisions is discussed.