Deep Inelastic Scattering Events with a LargeRapidity Gap at HERAH 1 Collaboration

Evidence is presented using data taken with the H1 detector at HERA for a class of deep inelastic electron{proton scattering (DIS) events (5 < Q 2 < 120 GeV 2) at low Bjorken-x (10 ?4 < x < 10 ?2) which have almost no hadronic energy ow in a large interval of pseudo-rapidity around the proton remnant direction and which cannot be attributed to our present understanding of DIS and uctuations in-nal state hadronic fragmentation. From an integrated luminosity of 273 nb ?1 , 734 events, that is about 5% of the total DIS sample, have no energy deposition greater than 400MeV forward of laboratory pseudo-rapidity max = 1:8 up to the largest measurable pseudo-rapidity of about 3:65. Evidence that about 10% of observed rapidity gap events are exclusive vector meson electroproduction is presented. Good descriptions of the data are obtained using models based either on a vector meson dominance like picture, which includes a large fraction of inelastic virtual photon dissociation, or on deep inelastic electron{pomeron scattering in which the partonic sub{structure of the latter is resolved.