# Impact of Glasma on heavy quark observables in nucleus-nucleus collisions at LHC

## TL;DR

This paper investigates how the early Glasma stage in heavy-ion collisions affects charm quark observables, revealing a novel initial enhancement in nuclear modification factor and increased elliptic flow, aligning with experimental data.

## Contribution

It demonstrates that Glasma-induced charm quark dynamics significantly influence $R_{AA}$ and $v_2$, challenging standard drag-diffusion models in describing pre-thermal stages.

## Key findings

- Initial $R_{AA}$ enhancement at high $p_T$ due to Glasma effects
- Increased elliptic flow $v_2$ from Glasma dynamics
- Standard drag-diffusion models cannot simultaneously reproduce $R_{AA}$ and $v_2$

## Abstract

In the pre-thermal equilibrium stage of relativistic heavy-ion collisions, a strong quasi-classical transverse gluon field emerges at about $\tau_0 \simeq 0.1 \, \rm fm/c$ and evolves together with their longitudinal counterparts according to the classical Yang-Mills (CYM) equations. Recently it has been shown that these fields induce a diffusion of charm quarks in momentum space resulting in a tilt of their spectrum without a significant drag. We find that in nucleus-nucleus collisions at LHC such a novel dynamics of charm quarks leads to an initial enhancement of the nuclear modification factor ($R_{AA}$) at $p_T$ larger than 2 GeV$/c$ contrary to the standard lore. Moreover, the same dynamics leads to a larger final elliptic flow ($v_2$) inducing a relation between $R_{AA}$ and $v_2$ that is quite close to the experimental measurements. Our study also shows that such an initial pre-thermal stage is unlikely to be described in terms of a standard drag and diffusion dynamics, because even if one tune such coefficients to reproduce the same $R_{AA}(p_T)$ this would imply a significantly smaller $v_2$.