Diffractive leptoproduction of small masses in QCD

In this paper we consider the process of diffraction dissociation in deep inelastic scattering in which a small mass is produced. This process is analyzed by calculating <(q)over bar q> <(q)over bar qG> production. We show that the small distance contributions (r(perpendicular to) proportional to 1/Q) to the longitudinal polarized virtual photon dominate the diffractive channels. Formulae for the cross section using the gluon density are written within the framework of perturbative QCD. We show that the production of small masses by a transverse polarized photon is concentrated at moderate values of r(perpendicular to) similar to 1 GeV-1, where the pQCD approach is valid. It is shown that only <(q)over bar q> pair production contributes to diffraction dissociation with beta > 0.4, and the possibility to extract the values of the gluon density from the measurements in this kinematic region is discussed. Shadowing corrections are assessed for both longitudinal and transverse polarized photons, and estimates of the different damping factors are given. The relation between diffractive production and the corrections to F-2 is alluded to. The evolution of the diffractive structure function is studied and a solution to the diffractive evolution equations is proposed. (C) 1997 Elsevier Science B.V.