Measurement of inclusive prompt photon photoproduction at HERA

TL;DR

This paper reports the first measurements of isolated prompt photon production in photoproduction at HERA, comparing experimental data with theoretical models and QCD calculations to test their accuracy.

Contribution

It provides the first inclusive measurements of prompt photons in photoproduction at HERA and compares them with various theoretical predictions.

Findings

Good agreement in the forward region with models

Models underestimate data in the rear direction

Provides data to test photon structure models

Abstract

First inclusive measurements of isolated prompt photons in photoproduction at the HERA ep collider have been made with the ZEUS detector, using an integrated luminosity of 38.4 pb$^{-1}$. Cross sections are given as a function of the pseudorapidity and the transverse energy ($\eta^\gamma$, \eTg) of the photon, for $\eTg > $ 5 GeV in the $\gamma p$ centre-of-mass energy range 134-285 GeV. Comparisons are made with predictions from Monte Carlo models having leading-logarithm parton showers, and with next-to-leading-order QCD calculations, using currently available parameterisations of the photon structure. For forward $\eta^\gamma$ (proton direction) good agreement is found, but in the rear direction all predictions fall below the data.