Correlations and the ridge in the Color Glass Condensate beyond the glasma graph approximation

TL;DR

This paper advances the understanding of two-gluon production in dilute-dense collisions within the Color Glass Condensate framework by going beyond the glasma graph approximation, analyzing correlations, and identifying key contributions.

Contribution

It extends the CGC framework beyond the dilute limit, clarifies the relation between glasma graphs and $k_T$-factorization, and isolates classical, HBT, and Bose enhancement effects in gluon correlations.

Findings

HBT and Bose enhancement contributions persist beyond higher-order density corrections.

Bose enhancement is suppressed relative to uncorrelated contributions.

Results are demonstrated using a simple numerical toy model.

Abstract

We consider two-gluon production in dilute-dense collisions within the Color Glass Condensate framework, applicable to both proton-nucleus and heavy-light ion collisions. We go beyond the glasma graph approximation which is valid in the dilute-dilute limit and show the correspondence between the glasma graphs and the $k_T$-factorized approach that we use in our calculation. We then identify the classical uncorrelated, and the Hanbury-Brown-Twiss (HBT) and Bose enhancement correlated contributions, with the Bose enhancement contribution being suppressed by the number of degrees of freedom with respect to the uncorrelated piece. We show that both the HBT and the Bose enhancement pieces survive the inclusion of higher order contributions in density and that they stem from the quadrupole piece of the two-gluon inclusive cross section. Finally, we illustrate the results using a toy model that allows a simple numerical implementation.