Angular distribution of medium-induced QCD cascades

TL;DR

This paper analytically describes the angular distribution of gluons in medium-induced QCD cascades, identifying soft and hard components and providing a complete solution beyond the diffusion approximation, relevant for jet shape studies in heavy-ion collisions.

Contribution

It offers a comprehensive analytical framework for the angular distribution of gluons in QCD cascades, including a power series solution beyond the diffusion approximation.

Findings

Identified soft and hard components in gluon angular distribution.

Derived the boundary angle analytically as a function of gluon energy and medium size.

Provided a power series solution for the cascade dynamics.

Abstract

We provide a complete description of the angular distribution of gluons in a medium-induced QCD cascade. We identify two components in the distribution, a soft component dominated by soft multiple scatterings, and a hard component dominated by a few hard scatterings. The typical angle that marks the boundary between these two components is determined analytically as a function of the energy of the observed gluon and the size of the medium. We construct the complete solution (beyond the diffusion approximation) in the regime where multiple branchings dominate the dynamics of the cascade in the form of a power series in the number of collisions with the medium particles. The coefficients of this expansions are related to the moments of the distribution in the diffusion approximation and are determined analytically. The angular distribution may be useful in phenomenological studies of jet shapes in heavy-ion collisions.