The $D^*/D$ ratio in heavy ion collisions

TL;DR

This paper investigates the $D^*/D$ ratio in heavy ion collisions, showing it remains roughly constant during the hadron gas phase despite increasing multiplicities, indicating charm mesons are near chemical equilibrium.

Contribution

It provides a theoretical calculation of the $D^*/D$ ratio's behavior during the hadron gas phase using an effective Lagrangian approach and estimates its dependence on system size.

Findings

The $D^*/D$ ratio remains approximately constant over time.

The ratio is nearly independent of system size.

Charm mesons are close to chemical equilibrium in the hadron gas phase.

Abstract

In this work we study the $D^*$ and $D$ multiplicities and how they change during the hadron gas phase of heavy ion collisions. With the help of an effective Lagrangian formalism, we calculate the production and absorption cross sections of the $D^*$ and $D$ mesons in a hadronic medium. We compute the time evolution of the abundances and the ratio $D^* /D$. They are approximately constant in time. Also, assuming a Bjorken type cooling and using an empirical relation between the freeze-out temperature and the central multiplicity density, we estimate $D^* /D$ as a function of $ dN /d \eta (\eta =0)$, which represents the system size. We find that, while the number of $D^*$'s and $D$'s grows significantly with the system size, their ratio remains approximately constant. This prediction can be compared with future experimental data. Our results suggest that the charm meson interactions in the hadron gas do not change their multiplicities and consequently these mesons are close to chemical equilibrium.