Color Transparency and Saturation in QCD

Abstract

We review the theoretical interpretation of deep-inelastic electron-proton scattering at low values of the Bjorken variable x Q 2 /W 2 < ∼ 0.1. The process proceeds via the interaction of quark-antiquark (qq) color-dipole fluctuations of the (virtual) photon with the proton. In terms of the forward Compton scattering amplitude, two reaction channels contribute to the interaction of the qq color dipole with the gluon field in the proton. Dependent on the kinematics, there is either color transparency, corresponding to a cancellation of the amplitudes for the two reaction channels, or saturation, occuring when the process is dominated by a single interaction channel. The connection between the color-dipole picture and the pQCD improved parton model is elaborated upon.