The broad away side of azimuthal correlations: 3 vs 2 final state particles in high energy nuclear collisions

TL;DR

This paper investigates the origin of the broad and double hump structures in azimuthal correlations of particles in high energy nuclear collisions, highlighting the role of three-particle final states and medium effects.

Contribution

It introduces a scenario where three-particle final states are enhanced in A+A collisions due to geometry and energy loss, explaining the observed correlation structures.

Findings

Three-particle processes contribute to azimuthal correlation structures.

Medium effects suppress two-particle processes more than three-particle ones.

Double hump structures are linked to enhanced three-particle final states in A+A collisions.

Abstract

In high energy heavy ion collisions at RHIC there are important aspects of the medium induced dynamics, that are still not well understood. In particular, there is a broadening and even a double hump structure of the away-side peak appearing in azimuthal correlation studies in Au+Au collisions which is absent in p+p collisions at the same energies. These features are already present but suppressed in p+p collisions: 2 to 3 parton processes produce such structures but are suppressed with respect to 2 to 2 processes. We argue that in A+A collisions the different geometry for the trajectories of 3 as opposed to 2 particles in the final state, together with the medium induced energy loss effects on the different cross sections, create a scenario that enhances processes with 3 particles in the final state, which gives on average this double hump structure.