Abstract
The photoproduction of isolated photons, both inclusive and together with a jet, has been measured with the ZEUS detector at HERA using an integrated luminosity of 374 pb−1. Differential cross sections are presented in the isolated-photon transverse-energy and pseudorapidity ranges 6<ETγ<15 GeV and −0.7<ηγ<0.9, and for jet transverse-energy and pseudorapidity ranges 4<ETjet<35 GeV and −1.5<ηjet<1.8, for exchanged-photon virtualities Q2<1 GeV2. Differential cross sections are also presented for inclusive isolated-photon production as functions of the transverse energy and pseudorapidity of the photon. Higher-order theoretical calculations are compared to the results.
Highlights
Events containing an isolated high-energy photon can provide a direct probe of the underlying partonic process in high-energy collisions involving hadrons, since the emission of such photons is largely unaffected by parton hadronisation
In ep collisions at HERA, the ZEUS and H1 Collaborations have previously reported the production of isolated photons in photoproduction [2,3,4,5,6,7], in which the exchanged virtual photon is quasi-real, and in deep inelastic scattering (DIS) [8,9,10,11]
The measurements are based on a data sample corresponding to an integrated luminosity of 374 ± 7 pb−1, taken during the years 2004 to 2007 with the ZEUS detector at HERA
Summary
Events containing an isolated high-energy photon can provide a direct probe of the underlying partonic process in high-energy collisions involving hadrons, since the emission of such photons is largely unaffected by parton hadronisation. Processes of this kind have been studied in a number of fixed-target and hadroncollider experiments [1]. Such processes are suppressed by requiring that the photon be isolated. Calculations based on the kT -factorisation approach have been made by Lipatov, Malyshev and Zotov (LMZ) [14,15,16]
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