Collisional energy loss of a fast heavy quark in a quark-gluon plasma

TL;DR

This paper calculates the collisional energy loss of a high-energy heavy quark in a quark-gluon plasma, including previously overlooked effects, and discusses uncertainties and bounds relevant for RHIC experiments.

Contribution

It provides a comprehensive calculation of collisional energy loss, including collinear logarithms and running coupling effects, extending previous models.

Findings

Logarithmic enhancement in energy loss coefficient.

Identification of a collinear logarithm from u-channel exchange.

Large theoretical uncertainties under RHIC conditions.

Abstract

We discuss the average collisional energy loss dE/dx of a heavy quark crossing a quark-gluon plasma, in the limit of high quark energy E >> M^2/T, where M is the quark mass and T >> M is the plasma temperature. In the fixed coupling approximation, at leading order dE/dx \propto \alpha_s^2, with a coefficient which is logarithmically enhanced. The soft logarithm arising from t-channel scattering off thermal partons is well-known, but a collinear logarithm from u-channel exchange had previously been overlooked. We also determine the constant beyond those leading logarithms. We then generalize our calculation of dE/dx to the case of running coupling. We estimate the remaining theoretical uncertainty of dE/dx, which turns out to be quite large under RHIC conditions. Finally, we point out an approximate relation between dE/dx and the QCD Debye mass, from which we derive an upper bound to dE/dx for all quark energies.