QCD antenna radiative spectrum in dense media within the Improved Opacity Expansion

TL;DR

This paper calculates the soft gluon emission spectrum from a quark-antiquark pair in dense QCD media, incorporating both hard and soft scatterings to improve jet quenching models and understand color decoherence effects.

Contribution

It introduces an analytically tractable framework using the Improved Opacity Expansion to include both single hard and multiple soft scatterings in gluon emission spectra.

Findings

Hard scatterings significantly alter large-angle gluon emissions.

Color coherence is rapidly lost due to rare hard scatterings.

The framework simplifies complex interactions into manageable expressions.

Abstract

We compute the double differential inclusive spectrum for the emission of a soft gluon from a color-singlet $q\bar q$ pair traversing a dense QCD medium. Our results extend the existing literature by simultaneously incorporating both single hard and multiple soft gluon exchanges between the jet and the medium -- an essential ingredient for a complete phenomenological description of jet quenching. Using the Improved Opacity Expansion framework, we provide an analytically tractable treatment, reducing the full cross-section to a set of simple expressions. Our analysis demonstrates that rare hard (Moli\`ere) scatterings significantly modify the gluon spectrum at large angles, accelerating the loss of color coherence between the initial quarks. We further quantify whether the modifications are driven by an overall weakening of the interference term, or by more detailed modifications to the fragmentation pattern. Our results provide a direct input for phenomenological jet quenching studies, offering new insights into the role of color decoherence in QCD matter.