Mass effect and coherence in medium-induced QCD radiation off a $q {\bar q}$ antenna

TL;DR

This paper calculates the medium-induced gluon radiation spectrum from a massive quark-antiquark antenna in QCD, revealing how interference effects depend on the antenna's opening angle and gluon softness, with implications for energy loss.

Contribution

It provides the first calculation of the medium-induced radiation spectrum off a massive $q \bar{q}$ antenna, highlighting interference effects and their dependence on geometry and gluon energy.

Findings

Interference dominates soft gluon radiation at small opening angles.

The spectrum is collinear finite but infrared divergent, differing from independent emitters.

Mass effects on energy loss are similar in different regimes.

Abstract

The medium-induced one-gluon radiation spectrum off a massive quark-antiquark ($q {\bar q}$) antenna traversing a colored QCD medium is calculated in this contribution. The gluon spectrum off the antenna computed at first order in the opacity expansion is collinear finite but infrared divergent, which is different from the result obtained from an independent emitter which is both infrared and collinear finite. The interference between emitters dominates the soft gluon radiation when the antenna opening angle is small and the emitted gluon is soft, whereas the antenna behaves like a superposition of independent emitters when the opening angle is large and the radiated gluon is hard. As a phenomenological consequence, we investigate the energy lost by the projectiles due to the radiation. In general, the size of the mass effects is similar in both cases.