We analyze the dissociation of a photon in diffractive deep inelastic scattering in the kinematic regime where the diffractive mass is much bigger than the photon virtuality. We consider the dominant $q\overline{q}g$ component keeping track of the transverse momentum of the gluon which can be measured as a final-state jet. We show that the diffractive gluon-jet production cross-section is strongly sensitive to unitarity constraints. In particular, in a model with parton saturation, this cross-section is sensitive to the scale at which unitarity effects become important, the saturation scale. We argue that the measurement of diffractive jets at HERA in the limit of high diffractive mass can provide useful information on the saturation regime of QCD.

• Received 27 April 2005

DOI:https://doi.org/10.1103/PhysRevD.71.114005