Measurement of isolated photons accompanied by jets in deep inelastic ep scattering

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 326pb -1. Measurements were made for exchanged photon virtualities, Q 2, in the range 10 to 350GeV 2. The photons were measured in the transverse-energy and pseudorapidity ranges 4<ET<15GeV and -0.7<η<0.9, and the jets were measured in the transverse-energy and pseudorapidity ranges 2.5<ET<35GeV 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%. © 2012 Elsevier B.V

Further studies of the photoproduction of isolated photons with a jet at HERA

“…In photoproduction processes in ep collisions at HERA, the exchanged virtual photon is quasi-real, with small virtuality, Q 2 , conventionally required to be less than 1 GeV 2 . These measurements follow earlier analyses of isolated photons in photoproduction by the ZEUS and H1 collaborations [2][3][4][5][6][7], as well as in deep inelastic scattering (DIS) [8][9][10][11]. In the analysis presented here, the most recent ZEUS photoproduction measurements are extended, using the same data as used previously.…”

“…The photon signal was extracted statistically following the approach used in previous ZEUS analyses [1,[8][9][10][11]. The method made use of the energyweighted width, measured in the Z direction, of the BEMC energy-cluster comprising the photon candidate.…”

Further studies of isolated photon production with a jet in deep inelastic scattering at HERA

“…Deep inelastic neutral current (NC) ep scattering (DIS), in which the exchanged photon has virtuality Q 2 > 1 GeV 2 , has also been measured in a variety of Q 2 ranges [16][17][18]. The analysis presented here extends an earlier ZEUS measurement of isolated photons and jets in DIS [19]. Figure 1 shows leading-order diagrams for high-energy photon production in DIS.…”

“…In the previous ZEUS publication on this topic [19], kinematic distributions of the outgoing photon and the jet were studied. Using the same data set, the analysis is extended here by measuring variables that involve two of the outgoing photon, the jet and the scattered electron.…”

“…At the third level, the full event was reconstructed and tighter requirements for a DIS electron were made. Offline selections, similar to those of the earlier ZEUS analysis [19], were then applied.…”