Eur. Phys. J. C (2008) 54: 371-387
https://doi.org/10.1140/epjc/s10052-008-0541-6

Regular Article - Experimental Physics

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

^* e-mail: diaconu@cppm.in2p3.fr

Received: 28 November 2007
Revised: 18 December 2007
Published online: 19 February 2008

Abstract

The production of isolated photons in deep-inelastic scattering ep→eγX is measured with the H1 detector at HERA. The measurement is performed in the kinematic range of negative four-momentum transfer squared 4<Q²<150 GeV² and a mass of the hadronic system W_X>50 GeV. The analysis is based on a total integrated luminosity of 227 pb^-1. The production cross section of isolated photons with a transverse energy in the range 3<E_T ^γ<10 GeV and pseudorapidity range -1.2<η^γ<1.8 is measured as a function of E_T ^γ, η^γ and Q². Isolated photon cross sections are also measured for events with no jets or at least one hadronic jet. The measurements are compared with predictions from Monte Carlo generators modelling the photon radiation from the quark and the electron lines, as well as with calculations at leading and next to leading order in the strong coupling. The predictions significantly underestimate the measured cross sections.