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

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.