Angular distribution of medium-induced QCD cascades

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.