# Studies of the diffractive photoproduction of isolated photons at HERA

## TL;DR

This study measures the diffractive photoproduction of isolated photons at HERA, compares results with models, and finds evidence for direct Pomeron interactions at high momentum fractions.

## Contribution

It provides the first detailed measurement of isolated photon production in diffractive events at HERA, highlighting deviations from models and evidence for direct Pomeron interactions.

## Key findings

- Data exceeds Rapgap predictions for high $z^{meas}_{Pomeron}$ values.
- Evidence supports the presence of direct Pomeron interactions.
- Kinematic variables analyzed show specific deviations from theoretical models.

## 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 transverse-energy and pseudorapidity ranges $5 < E_T < 15$ GeV and $-0.7 < \eta < 0.9,$ inclusively and also with a jet with transverse energy and pseudorapidity in the ranges $4 < E_{jet} < 35$ GeV and $-1.5 < \eta_{jet} < 1.8,$ using a total integrated electron-proton luminosity of 456 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 $z^{meas}_{Pomeron} > 0.9,$ where $z^{meas}_{Pomeron}$ 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.