Saturation of Nuclear Partons: the Fermi Statistics or Nuclear Opacity?

Abstract

We derive the two-plateau momentum distribution of final state (FS) quarks produced in deep inelastic scattering (DIS) off nuclei in the saturation regime. The diffractive plateau which dominates for small transverse momentum p measures precisely the momentum distribution of quarks in the beam photon, the role of the nucleus is simply to provide an opacity. The plateau for truly inelastic DIS exhibits a substantial nuclear broadening of the FS momentum distribution. We discuss the relationship between the FS quark densities and the properly defined initial state (IS) nuclear quark densities.The Weizs\"acker-Williams glue of a nucleus exhibits a substantial nuclear dilution, still soft IS nuclear sea saturates because of the anti-collinear splitting of gluons into sea quarks.