Eur. Phys. J. C (2010) 66: 17-33
https://doi.org/10.1140/epjc/s10052-010-1240-7

Regular Article - Experimental Physics

Prompt photons in photoproduction at HERA

¹ I. Physikalisches Institut der RWTH, Aachen, Germany
² Vinca Institute of Nuclear Sciences, Belgrade, Serbia
³ School of Physics and Astronomy, University of Birmingham, Birmingham, UK
⁴ Inter-University Institute for High Energies ULB-VUB, Brussels, Belgium
⁵ Universiteit Antwerpen, Antwerpen, Belgium
⁶ National Institute for Physics and Nuclear Engineering (NIPNE), Bucharest, Romania
⁷ Rutherford Appleton Laboratory, Chilton, Didcot, UK
⁸ Institute for Nuclear Physics, Cracow, Poland
⁹ Institut für Physik, TU Dortmund, Dortmund, Germany
¹⁰ Joint Institute for Nuclear Research, Dubna, Russia
¹¹ CEA, DSM/Irfu, CE-Saclay, Gif-sur-Yvette, France
¹² DESY, Hamburg, Germany
¹³ Institut für Experimentalphysik, Universität Hamburg, Hamburg, Germany
¹⁴ Max-Planck-Institut für Kernphysik, Heidelberg, Germany
¹⁵ Physikalisches Institut, Universität Heidelberg, Heidelberg, Germany
¹⁶ Kirchhoff-Institut für Physik, Universität Heidelberg, Heidelberg, Germany
¹⁷ Institute of Experimental Physics, Slovak Academy of Sciences, Košice, Slovak Republic
¹⁸ Department of Physics, University of Lancaster, Lancaster, UK
¹⁹ Department of Physics, University of Liverpool, Liverpool, UK
²⁰ Queen Mary and Westfield College, London, UK
²¹ Physics Department, University of Lund, Lund, Sweden
²² CPPM, CNRS/IN2P3—Univ. Mediterranee, Marseille, France
²³ Departamento de Fisica Aplicada, CINVESTAV, Mérida, Yucatán, Mexico
²⁴ Departamento de Fisica, CINVESTAV, México City, Mexico
²⁵ Institute for Theoretical and Experimental Physics, Moscow, Russia
²⁶ Lebedev Physical Institute, Moscow, Russia
²⁷ Max-Planck-Institut für Physik, München, Germany
²⁸ LAL, Univ. Paris-Sud, CNRS/IN2P3, Orsay, France
²⁹ LLR, Ecole Polytechnique, CNRS/IN2P3, Palaiseau, France
³⁰ LPNHE, Universités Paris VI and VII, CNRS/IN2P3, Paris, France
³¹ Faculty of Science, University of Montenegro, Podgorica, Montenegro
³² Institute of Physics, Academy of Sciences of the Czech Republic, Praha, Czech Republic
³³ Faculty of Mathematics and Physics, Charles University, Praha, Czech Republic
³⁴ Dipartimento di Fisica Università di Roma Tre and INFN Roma 3, Roma, Italy
³⁵ Institute for Nuclear Research and Nuclear Energy, Sofia, Bulgaria
³⁶ Institute of Physics and Technology of the Mongolian Academy of Sciences, Ulaanbaatar, Mongolia
³⁷ Paul Scherrer Institut, Villigen, Switzerland
³⁸ Fachbereich C, Universität Wuppertal, Wuppertal, Germany
³⁹ Yerevan Physics Institute, Yerevan, Armenia
⁴⁰ DESY, Zeuthen, Germany
⁴¹ Institut für Teilchenphysik, ETH, Zürich, Switzerland
⁴² Physik-Institut der Universität Zürich, Zürich, Switzerland

^* e-mail: sschmitt@mail.desy.de
^** e-mail: kruegerk@mail.desy.de

Received: 29 October 2009
Revised: 18 December 2009
Published online: 28 January 2010

Abstract

The production of prompt photons is measured in the photoproduction regime of electron–proton scattering at HERA. The analysis is based on a data sample corresponding to a total integrated luminosity of 340 pb⁻¹ collected by the H1 experiment. Cross sections are measured for photons with transverse momentum and pseudorapidity in the range  GeV and −1.0<η ^γ <2.4, respectively. Cross sections for events with an additional jet are measured as a function of the transverse energy and pseudorapidity of the jet, and as a function of the fractional momenta x _γ and x _p carried by the partons entering the hard scattering process. The correlation between the photon and the jet is also studied. The results are compared with QCD predictions based on the collinear and on the k _T factorization approaches.