Diffractive deep inelastic scattering at HERA

At HERA, about 10% of the deep inelastic events present a large rapidity gap in the hadronic final state, attributed to the exchange of a colour singlet system. A pomeron and a secondary reggeon exchange are needed in order to explain the data in terms of Regge phenomenology. A QCD analysis of the extracted structure function for the pomeron exchange indicates parton distributions dominated by a gluon carrying a large fraction of the exchange momentum at low Q2. This behaviour is confirmed in measurements of the hadronic final states. The usage of leading proton spectrometers allows the measurement of additional kinematic variables