# Effect of pre-equilibrium phase on $R_{AA}$ and $v_2$ of heavy quarks in heavy ion collisions

## TL;DR

This study investigates how the pre-equilibrium phase influences heavy quark suppression and flow in heavy ion collisions, finding a significant effect on $R_{AA}$ but negligible on $v_2$, and suggests early thermalization can mimic pre-equilibrium effects.

## Contribution

It demonstrates that the pre-equilibrium phase significantly affects $R_{AA}$ and can be approximated by early thermalized QGP conditions, providing insights into initial state modeling.

## Key findings

- Pre-equilibrium phase impacts $R_{AA}$ by 20-25%.
- Impact on $v_2$ from pre-equilibrium is negligible.
- Early thermalized QGP can mimic pre-equilibrium effects.

## Abstract

Heavy quark $R_{AA}$ and $v_2$ have been calculated at RHIC energy considering initial conditions with and without pre-equilibrium phase to highlight the effect of the latter on heavy quark observables. The momentum evolution of the heavy quark has been studied by means of the Boltzmann transport equation. To model the pre-equilibrium phase we have used the KLN initial condition. We have found that the pre-equilibrium phase impacts the $R_{AA}$ of about 20-25 $\%$ whereas the impact on $v_2$ is very negligible. We have also calculated heavy quark $R_{AA}$ and $v_2$ in the case of initializations with early thermalized quark-gluon plasma. We have checked that the particular form of the initial spectrum is not very important for $R_{AA}$, the larger energy density being more important. In fact, comparing the results obtained within the two initializations we have found that one can mimic the impact of the pre-equilibrium phase using a early thermalized QGP medium.