Parton saturation scaling function for exclusive production of vector mesons and deeply virtual Compton scattering

We provide a universal expression of cross sections for the exclusive vector meson production and deeply virtual Compton scattering (DVCS) in photon-proton and photon-nucleus interactions based on the geometric scaling phenomenon. The theoretical parametrization based on the scaling property depends only on the single variable τA=Q2/Qsat2, where the saturation scale, Qsat, drives the energy dependence and the corresponding nuclear effects. This phenomenological result describes all available data from DESY-HERA for ρ,ϕ,J/ψ production and DVCS measurements. A discussion is also carried out on the size of nuclear shadowing corrections on photon-nucleus interaction.