The problem of “saturation” in DIS and heavy-ion collisions

Abstract

The problem of saturation of parton densities in deep inelastic scattering (DIS) in the limit x → 0 and in heavy-ion collisions at very high energies is investigated in the framework of Reggeon theory. It is emphasized that the shadowing effects are important in a definite kinematical region. 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 allows one to describe structure functions of nuclei in the small-x region. It is shown how the prediction of the Glauber model for the density of hadrons produced in the central rapidity region in nucleus-nucleus interactions is modified due to shadowing of small-x partons. Calculations show that shadowing effects are important at RHIC energies, but the situation is far from saturation. Production of particles with large transverse momenta and jets is discussed.