# Radiative energy loss of neighboring subjets

## TL;DR

This paper calculates the probability distribution of energy loss for two neighboring subjets in a medium, revealing how their color coherence changes with angular separation, advancing understanding of jet quenching beyond single-parton models.

## Contribution

It provides the first leading-order calculation of in-medium energy loss for neighboring subjets, incorporating color decoherence effects and bridging the gap between single-parton and multi-parton jet quenching models.

## Key findings

- At small angles, subjets lose energy coherently as a single color charge.
- At large angles, subjets lose energy independently.
- The result models the gradual transition of color decoherence with angular separation.

## Abstract

We compute the in-medium energy loss probability distribution of two neighboring subjets at leading order, in the large-$N_c$ approximation. Our result exhibits a gradual onset of color decoherence of the system and accounts for two expected limiting cases. When the angular separation is smaller than the characteristic angle for medium-induced radiation, the two-pronged substructure lose energy coherently as a single color charge, namely that of the parent parton. At large angular separation the two subjets lose energy independently. Our result is a first step towards quantifying effects of energy loss as a result of the fluctuation of the multi-parton jet substructure and therefore goes beyond the standard approach to jet quenching based on single parton energy loss. We briefly discuss applications to jet observables in heavy-ion collisions.