Direct and resolved photoproduction at HERA with virtual and quasi-real photons

TL;DR

This study investigates dijet photoproduction in ep collisions at HERA, comparing virtual and quasi-real photons, revealing the decreasing role of resolved processes with increasing photon virtuality.

Contribution

It provides the first comparative analysis of direct and resolved photoproduction processes across different photon virtualities at HERA.

Findings

Resolved photon processes are observed in both virtual and quasi-real photon data.

The contribution of resolved processes decreases as photon virtuality increases.

Distributions of $x_{\gamma}^{obs}$ are sensitive to the balance of direct and resolved processes.

Abstract

Preliminary results are presented from a study of dijet photoproduction in ep collisions with both virtual and quasi-real photons at the ZEUS detector. Samples of events with photons of virtuality $P^2$ in the ranges $0.1 < P^2 < 0.55$ GeV$^2$ and $P^2 < 0.02$ GeV$^2$ having two jets of $E_T^{jet} > 4$ GeV in the final state have been obtained. For both quasi-real and virtual photons, uncorrected distributions of the quantity $x_{\gamma}^{obs}$, the fraction of the photon momentum manifest in the two highest $E_T$ jets, are presented. These distributions are sensitive to the relative contributions of the direct and resolved processes. Resolved photon processes are evident in both data sets, with an apparent decrease in the relative contribution from resolved processes as photon virtuality increases.