Interference Phenomena in Medium Induced Radiation

TL;DR

This paper investigates how interference effects influence medium-induced gluon radiation from a quark-antiquark pair in a QCD medium, revealing conditions under which interference is suppressed or absent, affecting jet quenching phenomena.

Contribution

It demonstrates the suppression of interference in medium-induced gluon radiation for large dipole angles within the BDMPS-Z regime, clarifying when radiation behaves as independent emissions.

Findings

Interference is suppressed for dipole angles much larger than a critical angle.

Medium-induced radiation equals the sum of independent emissions for large angles.

Radiation vanishes when the dipole angle is much smaller than the critical angle.

Abstract

We consider the interference pattern for the medium-induced gluon radiation produced by a color singlet quark-antiquark antenna embedded in a QCD medium with size $L$ and `jet quenching' parameter $\hat q$. Within the BDMPS-Z regime, we demonstrate that, for a dipole opening angle $\theta_{q\bar q} \gg\theta_c\equiv {2}/{\sqrt{\hat q L^3}}$, the interference between the medium--induced gluon emissions by the quark and the antiquark is suppressed with respect to the direct emissions. This is so since direct emissions are delocalized throughout the medium and thus yield contributions proportional to $L$ while interference occurs only between emissions at early times, when both sources remain coherent. Thus, for $\tqq \gg\theta_c$, the medium-induced radiation is the sum of the two spectra individually produced by the quark and the antiquark, without coherence effects like angular ordering. For $\tqq \ll\theta_c$, the medium--induced radiation vanishes.