Rapidity Gaps between Jets in Photoproduction at Hera H1 Collaboration

Photoproduction events which have two or more jets with transverse energy E T > 4:5 GeV have been studied in the p centre of mass energy range 158 GeV < W < 247 GeV with the H1 detector at HERA. The fraction f (() of events with a rapidity gap between the two highest E T jets is measured as a function of the rapidity separation between the jet axes. A gap is deened as the absence between the jets of any particle with energy E > 400 MeV. The gap fraction is observed to fall exponentially up to < 3:5. An excess of events with a large rapidity gap, over what would be expected from standard photoproduction processes, is observed for > 3:5. The excess can be interpreted as the result of the exchange of a strongly interacting colour singlet object.