Drag induced radiative loss from semi-hard heavy quarks

TL;DR

This paper revisits gluon bremsstrahlung from semi-hard heavy quarks in nuclear matter, revealing a new sensitivity to the drag parameter $ ext{ extgreek e}$, which affects heavy quark energy loss differently than light quarks.

Contribution

It introduces the first analysis showing heavy quark gluon emission depends on both transverse momentum diffusion and drag parameters, unlike previous models.

Findings

Heavy quark gluon spectrum is sensitive to $ ext{ extgreek e}$.

Additional energy loss term for semi-hard heavy quarks.

Negligible effect on light flavor energy loss.

Abstract

The case of gluon bremsstrahlung off a heavy quark in extended nuclear matter is revisited within the higher twist formalism. In particular, the in-medium modification of "semi-hard" heavy quarks is studied, where the momentum of the heavy quark is larger but comparable to the mass of the heavy quark ($p \gtrsim M$). In contrast to all prior calculations, where the gluon emission spectrum is entirely controlled by the transverse momentum diffusion parameter ($\hat q$), both for light and heavy quarks, in this work, we demonstrate that the gluon emission spectrum for a heavy quark (unlike that for flavors) is also sensitive to $\hat e$, which so far has been used to quantify the amount of light-cone drag experienced by a parton. This mass dependent effect, due to the non-light-like momentum of a semi-hard heavy-quark, leads to an additional energy loss term for heavy-quarks, while resulting in a negligible modification of light flavor (and high energy heavy flavor) loss. This result can be used to estimate the value of this sub-leading non-perturbative jet transport parameter ($\hat e$) from heavy flavor suppression in ultra-relativistic heavy-ion collisions.