Adding vacuum branching to jet evolution in a dense medium

TL;DR

This paper investigates how jet fragmentation in a dense quark-gluon plasma is affected by both vacuum-like emissions and medium-induced radiation, revealing modifications to the parton shower and aligning with LHC data.

Contribution

It introduces a factorization approach separating vacuum-like and medium-induced emissions, showing how the medium modifies the jet evolution at leading twist.

Findings

Medium reduces the radiation phase-space.

First emission outside the medium can violate angular ordering.

Results qualitatively match LHC measurements.

Abstract

We study the fragmentation of a jet propagating in a dense quark-gluon plasma. We show that the "vacuum-like" emissions triggered by the parton virtualities can be factorized from the medium-induced radiation responsible for the energy loss within a controlled, "double-logarithmic", approximation in perturbative QCD. We show that the collisions with the plasma constituents modify the vacuum-like parton shower already at leading twist, in two ways: the radiation phase-space is reduced and the first emission outside the medium can violate angular ordering. We compute the jet fragmentation function and find results in qualitative agreement with measurements at the LHC.