Measuring the photon fragmentation function at HERA |
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Authors: | A Gehrmann-De Ridder T Gehrmann E Poulsen |
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Institution: | 1. Institute for Theoretical Physics, ETH Zürich, 8093, Zürich, Switzerland 2. Institut für Theoretische Physik, Universit?t Zürich, Winterthurerstrasse 190, 8057, Zürich, Switzerland
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Abstract: | The production of final state photons in deep inelastic scattering originates from photon radiation off leptons or quarks
involved in the scattering process. Photon radiation off quarks involves a contribution from the quark-to-photon fragmentation
function, corresponding to the non-perturbative transition of a hadronic jet into a single, highly energetic photon accompanied
by some limited hadronic activity. Up to now, this fragmentation function was measured only in electron–positron annihilation
at LEP. We demonstrate by a dedicated parton-level calculation that a competitive measurement of the quark-to-photon fragmentation
function can be obtained in deep inelastic scattering at HERA. Such a measurement can be obtained by studying the photon energy
spectra in γ+(0+1)-jet events, where γ denotes a hadronic jet containing a highly energetic photon (the photon jet). Isolated
photons are then defined from the photon jet by imposing a minimal photon energy fraction. For this so-called democratic clustering
approach, we study the cross sections for isolated γ+(0+1)-jet and γ+(1+1)-jet production as well as for the inclusive isolated
photon production in deep inelastic scattering. |
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