Impact parameter dipole saturation model

Abstract

We develop a dipole model for DESY HERA deep inelastic scattering data which incorporates the impact parameter distribution of the proton. The model describes the inclusive total ${\ensuremath{\gamma}}^{*}p$ cross sections as well as the diffractive $J/\ensuremath{\psi}$ differential cross sections. We compare the model with previous approaches and show that the t distributions are sensitive to saturation phenomena. We estimate the boundary of the saturation region and show that it dominates the data in the low-${Q}^{2}$ region where the total ${\ensuremath{\gamma}}^{*}p$ cross section exhibits the same universal rise as hadronic cross sections. The model is then extended to nuclei and shows good agreement with the nuclear shadowing data at small x. Finally, we estimate the saturation scale in nuclei.