Photoproduction of events with rapidity gaps between jets at HERA

TL;DR

This paper investigates dijet photoproduction events with large rapidity gaps at HERA, finding an excess over standard models that suggests the exchange of a color-singlet object, supported by models including such exchanges.

Contribution

It provides experimental evidence for color-singlet exchange in photoproduction, which is not accounted for in standard models, and demonstrates the effectiveness of models including this exchange.

Findings

Clear excess of rapidity-gap events over standard predictions

Evidence supporting color-singlet exchange in photoproduction

Monte Carlo models with color-singlet exchange fit the data well

Abstract

The photoproduction of dijet events, where the two jets with the highest transverse energy are separated by a large gap in pseudorapidity, have been studied with the ZEUS detector using an integrated luminosity of 39 pb$^{-1}$. Rapidity-gap events are defined in terms of the energy flow between the jets, such that the total summed transverse energy in this region is less than some value $E_{\rm T}^{\rm CUT}$. The data show a clear excess over the predictions of standard photoproduction models. This is interpreted as evidence for a strongly interacting exchange of a color-singlet object. Monte Carlo models which include such a color-singlet exchange are able to describe the data.