Precision Measurement of the Prompt Photon Cross Section inpp¯Collisions ats=1.8

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

“…The calibration of the energies of the photon and scattered electron was taken from an earlier ZEUS analysis and used deeply virtual Compton scattering events [44]. The reconstructed transverse energy of the photon candidate, E γ T , was required to lie within the range 4 4 < E γ T < 15 GeV and the pseudorapidity, η γ , had to satisfy −0.7 < η γ < 0.9. Jets were reconstructed with the k T clustering algorithm [45] in the E scheme in the longitudinally invariant inclusive mode [46] with the R parameter set to 1.0.…”

“…4 The upper limit was selected to retain distinguishable shower shapes between the hadronic background and the photon signal.…”

“…Their production probes the underlying partonic process and can provide information on the structure of the proton. Processes of this type have been studied in a number of fixed-target and hadron-collider experiments [1][2][3][4][5][6][7][8][9][10]. The production of isolated photons in photoproduction, where the incoming photon is quasi-real, was previously studied at HERA by the ZEUS and H1 collaborations [11][12][13][14][15].…”

Unintegrated parton distributions and prompt photon hadroproduction

“…Equations (12) and (13) specify the missing parts of the delta functions in (10). As the variables η M and M have been used to specify the Lorentz boost it is convenient to write the integration over the luminosity in (10) in terms of dM 2 dη M dq 2 t .…”

“…Thus part of the observed p tγ comes from the initial partonic k t such that the hard subprocess singularity dσ/dt ∼ 1/p 4 tγ is approached more closely, and hence leads to a steeper p tγ spectrum. However in order to describe the observed spectra it is necessary to introduce a k t spectrum with an average value which increases from k t ∼ 0.5 GeV to more than 2 GeV [6] as the collision energy √ s increases from UA6, E706 [8,9] to Tevatron [10] energies. Such large partonic k t cannot originate solely from the large distance confinement domain, but must also have a significant perturbative QCD component.…”