Three and two-hadron correlations in \sqrt{s_{NN}}=200 GeV proton-proton and nucleus-nucleus collisions

TL;DR

This paper compares two- and three-hadron azimuthal correlations in proton-proton and nucleus-nucleus collisions at 200 GeV, revealing how parton energy loss affects correlation patterns and may explain experimental observations at RHIC.

Contribution

It introduces a perturbative QCD-based analysis of three- and two-hadron correlations, incorporating parton energy loss effects to explain azimuthal correlation shapes in heavy-ion collisions.

Findings

Two-to-three processes have different path length distributions than two-to-two.

Parton energy loss leads to an enhancement of three-hadron correlations.

The observed azimuthal correlation shapes at RHIC can be explained by these effects.

Abstract

We compare the azimuthal correlations arising from three and two hadron production in high energy proton-proton and nucleus-nucleus collisions at \sqrt{s_{NN}}=200 GeV, using the leading order matrix elements for two-to-three and two-to-two parton-processes in perturbative QCD. We first compute the two and three hadron production cross sections in mid-rapidity proton-proton collisions. Then we consider Au + Au collisions including parton energy loss using the modified fragmentation function approach. By examining the geometrical paths the hard partons follow through the medium, we show that the two away-side partons produced in two-to-three processes have in average a smaller and a greater path length than the average path length of the away-side parton in two-to-two processes. Therefore there is a large probability that in the former processes one of the particles escapes while the other gets absorbed. This effect leads to an enhancement in the azimuthal correlations of the two-to-three with respect to the two-to-two parton-processes when comparing to the same processes in proton-proton collisions since in average the particle with the shortest path length looses less energy with respect to the away side particle in two-to-two processes. We argue that this phenomenon may be responsible for the shape of the away-side in azimuthal correlations observed in mid-rapidity Au + Au collisions at RHIC.