Observation of hard scattering in photoproduction events with a large rapidity gap at HERA

Events with a large rapidity gap and a transverse energy greater than 5 GeV have been observed in quasi-real photoproduction at HERA with the ZEUS detector. The rate of these events as a function of the γp centre of mass energy is consistent with diffractive scattering. For transverse energies above 12 GeV, the hadronic final states show predominantly a two-jet structure with each jet having a transverse energy greater than 4 GeV. Thus, hard scattering has been observed in large rapidity gap, photoproduced interactions. For these events, little energy flow is observed between the jets and the pro- ton direction. These observations are consistent with the hard scattering of a quasi-real photon on partons in a colourless object in the proton