Diffractive production of isolated photons with the ZEUS detector at HERA

TL;DR

This paper measures the production of isolated photons in diffractive events at HERA, comparing results to models and finding evidence for direct Pomeron interactions beyond existing predictions.

Contribution

It provides the first detailed measurement of isolated photon production in diffractive processes at HERA, highlighting discrepancies with the RAPGAP model and suggesting direct Pomeron interactions.

Findings

Data exceeds RAPGAP predictions for z|P(meas)>0.9

Evidence for direct Pomeron interactions

Photon production cross sections measured in specified kinematic ranges

Abstract

The photoproduction of isolated photons has been measured in diffractive events recorded by the ZEUS detector at HERA. Cross sections are evaluated in the photon-proton transverse-energy and pseudorapidity ranges 5<ET(gamma)<15 GeV and -0.7<eta(gamma)<0.9 inclusively and also with a jet with transverse energy and pseudorapidity in the range 4<ET(jet)<35 GeV and -1.5<eta(jet)<1.8, using a total integrated electron-proton luminosity of 374 pb-1. A number of kinematic variables were studied and compared to predictions from the RAPGAP Monte Carlo model. An excess of data is observed above the RAPGAP predictions for z|P(meas)>0.9, where z|P(meas) is the fraction of the longitudinal momentum of the colourless "Pomeron" exchange that is transferred to the photon-jet final state, giving evidence for direct Pomeron interactions.