High-E_T dijet photoproduction at HERA

TL;DR

This paper reports measurements of high-E_T dijet production in photoproduction at HERA, providing insights into parton distributions in the photon and proton and testing QCD beyond next-to-leading order.

Contribution

First measurement of high-E_T dijet cross sections in photoproduction at HERA that constrains parton densities and tests QCD predictions beyond NLO.

Findings

Data sensitive to parton distributions in photon and proton

Results show effects beyond next-to-leading order QCD

Measurements can refine parton density models

Abstract

The cross section for high-E_T dijet production in photoproduction has been measured with the ZEUS detector at HERA using an integrated luminosity of 81.8 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 142 < W < 293 GeV. Events were selected if at least two jets satisfied the transverse-energy requirements of E_T(jet1) > 20 GeV and E_T(jet2) > 15 GeV and pseudorapidity requirements of -1 < eta(jet1,2) < 3, with at least one of the jets satisfying -1 < eta(jet) < 2.5. The measurements show sensitivity to the parton distributions in the photon and proton and effects beyond next-to-leading order in QCD. Hence these data can be used to constrain further the parton densities in the proton and photon.