# In-medium parton branching beyond eikonal approximation

## TL;DR

This paper advances the theoretical understanding of in-medium parton branching by calculating the gluon radiation spectrum beyond the eikonal approximation, confirming the validity of a probabilistic shower model in quark-gluon plasma.

## Contribution

It provides the first calculation of in-medium gluon radiation beyond the eikonal approximation using a quark-antiquark antenna setup, demonstrating factorization of broadening effects.

## Key findings

- Broadening effects can be factorized from radiation modifications.
- Probabilistic picture of parton shower evolution remains valid in QGP.
- Enhanced understanding of gluon emissions beyond eikonal accuracy.

## Abstract

The description of the in-medium modifications of partonic showers has been at the forefront of current theoretical and experimental efforts in heavy-ion collisions. It provides a unique laboratory to extend our knowledge frontier of the theory of the strong interactions, and to assess the properties of the hot and dense medium (QGP) that is produced in ultra-relativistic heavy-ion collisions at RHIC and the LHC. The theory of jet quenching, a commonly used alias for the modifications of the parton branching resulting from the interactions with the QGP, has been significantly developed over the last years. Within a weak coupling approach, several elementary processes that build up the parton shower evolution, such as single gluon emissions, interference effects between successive emissions and corrections to radiative energy loss of massive quarks, have been addressed both at eikonal accuracy and beyond by taking into account the Brownian motion that high-energy particles experience when traversing a hot and dense medium. In this work, by using the setup of single gluon emission from a color correlated quark-antiquark pair in a singlet state ($q\bar{q}$ antenna), we calculate the in-medium gluon radiation spectrum beyond the eikonal approximation. The results show that we are able to factorize broadening effects from the modifications of the radiation process itself. This constitutes the final proof that a probabilistic picture of the parton shower evolution holds even in the presence of a QGP.