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

TL;DR

This paper reports the observation of hard scattering events with large rapidity gaps in photoproduction at HERA, indicating diffractive processes with two-jet final states and minimal energy outside the jets.

Contribution

First observation of hard scattering in photoproduction events with large rapidity gaps at HERA, supporting diffractive scattering models with a quasi-real photon interacting with a colorless proton component.

Findings

Events with large rapidity gaps are consistent with diffractive scattering.

High transverse energy events show a two-jet structure with little outside energy.

Results support the hard scattering of a photon with a colorless proton component.

Abstract

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.