DPS in CGC: HBT correlations in double inclusive photon production

TL;DR

This paper develops a method within the CGC framework to analyze double parton scattering, revealing that prompt photon pairs exhibit HBT correlations that inform about nonperturbative parton distributions.

Contribution

It introduces a calculable approach to DPS in CGC using new 2GTMD functions and links HBT correlations in photon pairs to parton spatial distributions.

Findings

HBT correlations appear in prompt photon pairs from independent partons.

The HBT peak width relates to the proton's transverse size.

Prompt photon correlations can probe nonperturbative 2GTMDs.

Abstract

We introduce a technique to study double parton scattering (DPS) in the Color-Glass-Condensate (CGC) approach. We show that the cross-section of the DPS in the CGC approach is calculable in terms of new nonperturbative objects, generalized double transverse momentum-dependent parton distribution (2GTMD) functions. We investigate the production of pairs of prompt photons from two partons in the projectile hadron in high-energy proton-nucleus collisions. We show that even for independent partons in the projectile, the prompt photon correlation function exhibits Hanbury Brown and Twiss (HBT) correlations. The width of the HBT peak is controlled by the transverse distance between the parton of the pair, which is of the order of the proton size. Thus, the HBT measurements in two-particle production such as prompt photon pairs provide useful information about the nonperturbative 2GTMDs.