Estimating gluon saturation in dijet photoproduction in UPC

Abstract

We study dijet production in the ultra-peripheral heavy ion collisions (UPC) at LHC within the saturation formalism. More precisely, we use an approach which is the large-$p_T$ approximation to the Color Glass Condensate on one hand, and the small-$x$ limit of the transverse momentum dependent (TMD) factorization on the other. The direct component of the dijet production in UPC at small $x$ probes the so-called Weizsacker-Williams (WW) TMD gluon distribution, which is not accessible in more inclusive processes, where rather the dipole TMD gluon distribution is probed. Although the WW TMD gluon distribution is not known from data, it can be calculated from the data-restricted dipole TMD gluon distribution using the mean field approximation. Using such approximated WW distribution we calculate various dijet observables in UPC and estimate the saturation effects.