Diffusion of heavy quarks in the early stage of high-energy nuclear collisions at energies available at the BNL Relativistic Heavy Ion Collider and at the CERN Large Hadron Collider
Jun-Hong Liu, Salvatore Plumari, Santosh K. Das, Vincenzo Greco, Marco Ruggieri
Abstract
We study the diffusion of charm and beauty in the early stage of high-energy nuclear collisions at RHIC and LHC energies, considering the interaction of these heavy quarks with the evolving Glasma by means of the Wong equations, in the color-$SU(2)$ case. In comparison with previous works, we add the longitudinal expansion of the gluon medium as well as we estimate the diffusion coefficient in momentum space, and the effect of energy loss due to gluon radiation. We find that heavy quarks diffuse in the strong transverse color fields in the very early stage (0.2--0.3 fm/c) and this leads to a suppression at low ${p}_{T}$ and enhancement at intermediate low ${p}_{T}$. The shape of the observed nuclear suppression factor obtained within our calculations is in qualitative agreement with the experimental results of the same quantity for $D$ mesons in proton-nucleus collisions. We compute the nuclear suppression factor in nucleus-nucleus collisions as well, for both charm and beauty, finding a substantial impact of the evolving Glasma phase on these, suggesting that initialization of heavy quarks spectra in the quark-gluon plasma phase should not neglect the early evolution in the strong gluon fields.