# In-medium effects on particle production in heavy ion collisions

## TL;DR

This study investigates how in-medium modifications of nucleon-nucleon cross sections influence particle production in heavy ion collisions, highlighting the robustness of particle ratios as probes of the nuclear equation of state at high densities.

## Contribution

It demonstrates the density dependence of inelastic cross sections affects particle yields but not ratios, and evaluates kaon potentials using two schemes for consistent results.

## Key findings

- In-medium inelastic cross sections significantly affect pion and kaon yields.
- Particle ratios like $( ext{pi}^{-}/ ext{pi}^{+})$ and $(K^{0}/K^{+})$ are only moderately affected.
- Kaon potentials show a repulsive contribution, reducing effects on yield ratios.

## Abstract

The effect of possible in-medium modifications of nucleon-nucleon ($NN$) cross sections on particle production is investigated in heavy ion collisions ($HIC$) at intermediate energies. In particular, using a fully covariant relativistic transport approach, we see that the density dependence of the {\it inelastic} cross sections appreciably affects the pion and kaon yields and their rapidity distributions. However, the $(\pi^{-}/\pi^{+})$- and $(K^{0}/K^{+})$-ratios depend only moderately on the in-medium behavior of the inelastic cross sections. This is particularly true for kaon yield ratios, since kaons are more uniformly produced in high density regions. Kaon potentials are also suitably evaluated in two schemes, a chiral perturbative approach and an effective meson-quark coupling method, with consistent results showing a similar repulsive contribution for $K^{+}$ and $K^{0}$. As a consequence we expect rather reduced effects on the yield ratios. We conclude that particle ratios appear to be robust observables for probing the nuclear equation of state ($EoS$) at high baryon density and, particularly, its isovector sector.