Rapidity gaps between jets in Photoproduction at HERA

Photoproduction events which have two or more jets have been studied in the W_#gamma#_p range 135 GeV<W_#gamma#_p<280 GeV with the ZEUS detector at HERA. A class of events is observed with little hadronic activity between the jets. The jets are separated by pseudorapidity intervals (#DELTA##eta#) of up to four units and have transverse energies greater than 6 GeV. A gap is defined as the absence between the jets of particles with transverse energy greater than 300 MeV. The fraction of events containing a gap is measured as a function of #DELTA##eta#. It decreases exponentially as expected for processes in which colour is exchanged between the jets, up to a value of #DELTA##eta##approx#3, then reaches a constant value of about 0.1. The excess above the exponential fall-off can be interpreted as evidence for hard diffractive scattering via a strongly interacting colour singlet object. (orig.)25 refs.Available from TIB Hannover: RA 2999(95-194) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman