EMMI Workshop: Mining for gluon saturation at the LHC and the future EIC

We study the diffractive production of a massive quark pair in coherent photon-nucleus collisions within the Color Glass Condensate framework. We work in the correlation limit, where we explicitly distinguish between hard and semi-hard scales. In a first study, we consider the emission of an unmeasured semi-hard gluon with transverse momentum of the order of the saturation scale by the massive quark pair. In this regime, the differential cross section factorizes into a mass-dependent hard factor, which describes the formation of the quark-antiquark, and the diffractive gluon transverse momentum dependent (TMD) distribution. In a second study, we consider the production of a semi-hard quark and a hard antiquark and gluon, which have transverse momenta much larger than the saturation scale. We then factorize the differential cross section into a mass-independent hard factor and a mass-dependent quark diffractive TMD distribution. Our results are the base for future phenomenology predictions for quarkonium and open charm production in the saturation regime in ultraperipheral collisions at the LHC.