Abstract
The production of isolated high-energy photons accompanied by jets has been measured in deep inelastic ep scattering with the ZEUS detector at HERA, using an integrated luminosity of 326 pb−1. Measurements were made for exchanged photon virtualities, Q2, in the range 10 to 350 GeV2. The photons were measured in the transverse-energy and pseudorapidity ranges 4<ETγ<15 GeV and −0.7<ηγ<0.9, and the jets were measured in the transverse-energy and pseudorapidity ranges 2.5<ETjet<35 GeV and −1.5<ηjet<1.8. Differential cross sections are presented as functions of these quantities. Perturbative QCD predictions give a reasonable description of the shape of the measured cross sections over most of the kinematic range, but the absolute normalisation is typically in disagreement by 20–30%.
Highlights
Events in which an isolated high-energy photon is observed provide a direct probe of the underlying partonic process in highenergy collisions involving hadrons, since the emission of such photons is unaffected by parton hadronisation
In ep collisions at HERA, the ZEUS and H1 collaborations have previously reported the production of isolated photons in photoproduction [2,3,4,5,6], in which the exchanged photon is quasi-real, and in deep inelastic scattering (DIS) [7,8,9], where the virtuality Q 2 of the exchanged virtual photon is greater than 1 GeV2
By increasing the ratio of the prompt photon contribution relative to the lepton-radiated contributions, this measurement provides an improved test of perturbative QCD in a kinematic region with two hard scales, which are given by Q and by pjTet, the transverse momentum of the jet or, equivalently, the momentum transfer in the QCD scatter
Summary
Events in which an isolated high-energy photon is observed provide a direct probe of the underlying partonic process in highenergy collisions involving hadrons, since the emission of such photons is unaffected by parton hadronisation. Processes of this kind have been studied in a number of fixed-target and hadroncollider experiments [1]. By increasing the ratio of the prompt photon contribution relative to the lepton-radiated contributions, this measurement provides an improved test of perturbative QCD (pQCD) in a kinematic region with two hard scales, which are given by Q and by pjTet, the transverse momentum of the jet or, equivalently, the momentum transfer in the QCD scatter. A calculation based on the kT factorisation approach has been made by Baranov et al (BLZ) [14]
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