  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.
