Melting of $c \bar c$ and $b \bar b$ pairs in the pre-equilibrium stage of proton-nucleus collisions at the Large Hadron Collider

TL;DR

This paper investigates how heavy quark-antiquark pairs melt during the early, pre-equilibrium stage of high-energy proton-nucleus collisions at the LHC, emphasizing the role of color decorrelation in this process.

Contribution

It introduces a novel kinetic theory approach to quantify heavy quark pair melting during the glasma stage in proton-nucleus collisions.

Findings

Approximately 50% of $c\bar c$ and $b\bar b$ pairs melt within 0.4-0.5 fm/c after formation.

Color decorrelation is identified as the dominant melting mechanism.

The model relates pair melting probability to fluctuations in color charges.

Abstract

We study the melting of $c\bar c$ and $b\bar b$ pairs in the early stage of high-energy proton-nucleus collisions. We describe the early stage in terms of an evolving $SU(3)$ glasma stage, that is dominated by intense, out-of-equilibrium gluon fields. On top of these fields, we liberate heavy quark-antiquark pairs, whose constituents are let evolve according to relativistic kinetic theory coupled to the gluon fields. We define a pair-by-pair probability that the pair melts during the evolution, which we relate to the fluctuations of the color charges induced by the interaction of the quarks with the gluon fields. We find that color decorrelation is the main melting mechanism within the pre-equilibrium stage. Moreover, we estimate that within $\Delta \tau\approx0.4-0.5$ fm/c after the formation time of the pairs, about $50\%$ of $c\bar c$ and $b\bar b$ pairs are melted.