An Impact Parameter Dipole Saturation Model

Abstract

We develop a dipole model for HERA DIS data which incorporates the impact parameter distribution of the proton. The model describes the inclusive total $\gamma^*p$ cross-sections as well as the diffractive $J/\psi$ 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 $\gamma^*p$ 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.