Dijet photoproduction at HERA and the structure of the photon

TL;DR

This paper reports on measurements of dijet photoproduction at HERA, testing photon structure models by comparing experimental data with next-to-leading-order QCD predictions.

Contribution

It provides new experimental data on dijet cross sections in photoproduction, offering insights into the parton density of the photon and testing existing parameterisations.

Findings

Data are sensitive to the photon parton density.

Results agree with NLO QCD predictions within uncertainties.

Constraints on photon structure functions are improved.

Abstract

The dijet cross section in photoproduction has been measured with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb$^{-1}$. The events were required to have a virtuality of the incoming photon, $Q^2$, of less than 1 GeV$^2$ and a photon-proton centre-of-mass energy in the range $134 < W_{\gamma p} < 277$ GeV. Each event contains at least two jets satisfying transverse-energy requirements of $E_{T}^{\rm jet1}>14$ GeV and $E_{T}^{\rm jet2}>11$ GeV and pseudorapidity requirements of $-1<\eta^{\rm jet1,2}<2.4$. The measurements are compared to next-to-leading-order QCD predictions. The data show particular sensitivity to the density of partons in the photon, allowing the validity of the current parameterisations to be tested.