Diffractive processes and the problem of “saturation”

Unitarity effects in diffractive processes are investigated. It is emphasized that diffraction is closely related to the problem of saturation of parton densities in deep inelastic scattering (DIS) in the limit x→0 and to heavy ion collisions at very high energies. The model which includes unitarity effects and gives a good description of structure functions and diffractive processes in DIS is discussed. In the limit x→0 the “saturation” of parton densities is achieved. The Gribov approach to interaction with nuclei is used to describe structure functions of nuclei in the small x region and interactions of nuclei. Calculations show that for heavy ion collisions the shadowing effects are important at RHIC energies, but the “saturation” is not achieved yet.