Events with a large rapidity gap and total transverse energy greater than 5 GeV have been observed in quasi-real photoproduction at HERA with the ZEUS detector. The distribution of these events as a function of the gamma p centre of mass energy is consistent with diffractive scattering. For total 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. For the two-jet events, little energy flow is found outside the jets. This observation is consistent with the hard scattering of a quasi-real photon with a colourless object in the proton.
Derrick, M., Krakauer, D., Magill, S., Musgrave, B., Repond, J., Schlereth, J., et al. (1995). OBSERVATION OF HARD SCATTERING IN PHOTOPRODUCTION EVENTS WITH A LARGE RAPIDITY GAP AT HERA RID B-9165-2008 RID C-5889-2009 RID C-1693-2008. PHYSICS LETTERS. SECTION B, 346(3-4), 399-414 [10.1016/0370-2693(95)00022-D].