Two-particle correlations in high energy collisions and the gluon four-point function

TL;DR

This paper derives the evolution equation for the gluon four-point function at small x, revealing factorization breaking effects beyond leading order that influence two-gluon correlations in high energy collisions.

Contribution

It provides the first derivation of the rapidity evolution for the gluon four-point function including factorization breaking terms beyond the Gaussian approximation.

Findings

Factorization breaking terms contribute at leading order in Nc.

These terms affect two-gluon correlations as functions of rapidity and azimuthal angle.

The results are relevant for interpreting experimental data from RHIC and LHC.

Abstract

We derive the rapidity evolution equation for the gluon four-point function in the dilute regime and at small x from the JIMWLK functional equation. We show that beyond leading order in Nc the mean field (Gaussian) approximation where the four point function is factorized into a product of two point functions is violated. We calculate these factorization breaking terms and show that they contribute at leading order in Nc to correlations of two produced gluons as a function of their relative rapidity and azimuthal angle, for generic (rather than back-to-back) angles. Such two-particle correlations have been studied experimentally at the BNL-RHIC collider and could be scrutinized also for pp (and, in the future, also AA) collisions at the CERN-LHC accelerator.