Heavy quark diffusion in pre-equilibrium stage of heavy ion collisions

TL;DR

This paper calculates heavy quark drag and diffusion coefficients during the pre-equilibrium stage of heavy ion collisions, revealing rapid diffusion comparable to equilibrium phases, impacting experimental interpretations.

Contribution

It introduces a perturbative QCD framework to evaluate heavy quark transport coefficients in the pre-equilibrium gluonic phase using KLN and classical Yang-Mills spectra.

Findings

Heavy quarks experience similar drag in equilibrium and out-of-equilibrium gluonic systems.

Diffusion in the pre-equilibrium phase is as fast as in kinetically equilibrated gluons.

Pre-equilibrium diffusion exceeds that in chemically equilibrated quark-gluon plasma.

Abstract

The drag and diffusion coefficients of heavy quarks (HQs) have been evaluated in the pre-equilibrium phase of the evolving fireball produced in heavy ion collisions at RHIC and LHC energies. The KLN and classical Yang-Mills spectra have been used for describing the momentum distributions of the gluons produced just after the collisions but before they thermalize. The interaction of the HQs with these gluons has been treated within the framework of perturbative QCD. We have observed that the HQs are dragged almost equally by the kinetically equilibrated and out-of-equilibrium gluonic systems. We have also noticed that the HQs diffusion in the pre-equilibrium gluonic phase is as fast as in the kinetically equilibrated gluons. Moreover, the diffusion is faster in the pre-equilibrium phase than in the chemically equilibrated quark-gluon plasma. These findings may have significant impact on the analysis of experimental results on the elliptic flow and the high momentum suppression of the open charm and beauty hadrons.