Saturation and Diffractive DIS

Around 10% of deep inelastic scattering (DIS) events observed at HERA at small value of the Bjorken variable x are diffractive events [1, 2], when the incoming proton stays intact losing only a small fraction xIP of its initial momentum. A large rapidity gap is formed between the scattered proton (or its low mass excitation) and the diffractive system. The ratio of diffractive to total DIS cross sections is to a good approximation constant as a function of Q2. Thus in a first approximation, DIS diffraction is a leading twist effect with logarithmic scaling violation. Moreover, the same ratio as a function of x (or energy) is also constant. Theoretical models of diffraction should explain these facts.