Eur. Phys. J. C (2007) 49: 511-522
https://doi.org/10.1140/epjc/s10052-006-0134-1

Regular Article - Experimental Physics

Measurement of prompt photons with associated jets in photoproduction at HERA

¹ Argonne National Laboratory, Argonne, IL, 60439-4815, USA
² Andrews University, Berrien Springs, MI, 49104-0380, USA
³ Institut für Physik, Humboldt-Universität zu Berlin, Berlin, Germany
⁴ University and INFN Bologna, Bologna, Italy
⁵ Physikalisches Institut der Universität Bonn, Bonn, Germany
⁶ H.H. Wills Physics Laboratory, University of Bristol, Bristol, UK
⁷ Physics Department and INFN, Calabria University, Cosenza, Italy
⁸ Chonnam National University, Kwangju, South Korea
⁹ Jabatan Fizik, Universiti Malaya, 50603, Kuala Lumpur, Malaysia
¹⁰ Nevis Laboratories, Columbia University, Irvington on Hudson, NY, 10027, USA
¹¹ The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, Cracow, Poland
¹² Faculty of Physics and Applied Computer Science, AGH-University of Science and Technology, Cracow, Poland
¹³ Department of Physics, Jagellonian University, Cracow, Poland
¹⁴ Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany
¹⁵ Deutsches Elektronen-Synchrotron DESY, Zeuthen, Germany
¹⁶ University and INFN, Florence, Italy
¹⁷ Fakultät für Physik, Universität Freiburg i.Br., Freiburg i.Br., Germany
¹⁸ Department of Physics and Astronomy, University of Glasgow, Glasgow, UK
¹⁹ Department of Engineering in Management and Finance, Univ. of Aegean, Aegean, Greece
²⁰ Institute of Exp. Physics, Hamburg University, Hamburg, Germany
²¹ High Energy Nuclear Physics Group, Imperial College London, London, UK
²² KEK, Institute of Particle and Nuclear Studies, Tsukuba, Japan
²³ Institute of Physics and Technology of Ministry of Education and Science of Kazakhstan, Almaty, Kazakhstan
²⁴ Center for High Energy Physics, Kyungpook National University, Daegu, South Korea
²⁵ Institut de Physique Nucléaire, Université Catholique de Louvain, Louvain-la-Neuve, Belgium
²⁶ Departamento de Física Teórica, Universidad Autónoma de Madrid, Madrid, Spain
²⁷ Department of Physics, McGill University, Montréal, Québec, Canada H3A 2T8,
²⁸ Faculty of General Education, Meiji Gakuin University, Yokohama, Japan
²⁹ Moscow Engineering Physics Institute, Moscow, Russia
³⁰ Institute of Nuclear Physics, Moscow State University, Moscow, Russia
³¹ Max-Planck-Institut für Physik, München, Germany
³² NIKHEF and University of Amsterdam, Amsterdam, Netherlands
³³ Physics Department, Ohio State University, Columbus, OH, 43210, USA
³⁴ Department of Physics, University of Oxford, Oxford, UK
³⁵ Dipartimento di Fisica dell’ Università and INFN, Padova, Italy
³⁶ Department of Physics, Pennsylvania State University, University Park, PA, 16802, USA
³⁷ Polytechnic University, Sagamihara, Japan
³⁸ Dipartimento di Fisica, Università ’La Sapienza’ and INFN, Rome, Italy
³⁹ Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, UK
⁴⁰ Raymond and Beverly Sackler Faculty of Exact Sciences, School of Physics, Tel-Aviv University, Tel-Aviv, Israel
⁴¹ Department of Physics, Tokyo Institute of Technology, Tokyo, Japan
⁴² Department of Physics, University of Tokyo, Tokyo, Japan
⁴³ Tokyo Metropolitan University, Department of Physics, Tokyo, Japan
⁴⁴ Università di Torino and INFN, Torino, Italy
⁴⁵ Università del Piemonte Orientale, Novara, and INFN, Torino, Italy
⁴⁶ Department of Physics, University of Toronto, Toronto, Ontario, Canada M5S 1A7,
⁴⁷ Physics and Astronomy Department, University College London, London, UK
⁴⁸ Institute of Experimental Physics, Warsaw University, Warsaw, Poland
⁴⁹ Institute for Nuclear Studies, Warsaw, Poland
⁵⁰ Department of Particle Physics, Weizmann Institute, Rehovot, Israel
⁵¹ Department of Physics, University of Wisconsin, Madison, WI, 53706, USA
⁵² Department of Physics, York University, York, Ontario, Canada M3J 1P3,
⁵³ University College, London, UK
⁵⁴ Alexander von Humboldt Fellow, University of Hamburg, Hamburg, Germany
⁵⁵ Univ. of Wuppertal, Wuppertal, Germany
⁵⁶ DESY group FEB, Hamburg, Germany
⁵⁷ Argonne National Laboratory, Argonne, IL, USA
⁵⁸ Institut of Theoretical and Experimental Physics, Moscow, Russia
⁵⁹ INP, Cracow, Poland
⁶⁰ FPACS, AGH-UST, Cracow, Poland
⁶¹ DESY, Hamburg, Germany
⁶² ICEPP, University of Tokyo, Tokyo, Japan
⁶³ University of Tokyo, Tokyo, Japan
⁶⁴ CERN, Geneva, Switzerland
⁶⁵ Alexander von Humboldt Research Award, Max Planck Institute, Munich, Germany
⁶⁶ KEK, Tsukuba, Japan
⁶⁷ Department of Radiological Science, Tokyo Metropolitan University, Tokyo, Japan
⁶⁸ Łódź University, Łódź, Poland
⁶⁹ Łódź University, Łódź, Poland

^* e-mail: patricia.ball@durham.ac.uk

Received: 10 August 2006
Revised: 26 September 2006
Published online: 8 November 2006

Abstract

The photoproduction of prompt photons, together with an accompanying jet, has been studied in ep collisions at a centre-of-mass energy of 318 GeV with the ZEUS detector at HERA using an integrated luminosity of 77 pb^-1. Cross sections were measured for the transverse energy of the photon and the jet larger than 5 and 6 GeV, respectively. The differential γ+jet cross sections were reconstructed as functions of the transverse energy, pseudorapidity and x_γ ^obs, the fraction of the incoming photon momentum taken by the photon-jet system. Predictions based on leading-logarithm parton-shower Monte Carlo models and next-to-leading-order (NLO) QCD generally underestimate the cross sections for the transverse energies of prompt photons below 7 GeV, while the k_T-factorisation QCD calculation agrees with the data better. When the minimum transverse energy of prompt photons is increased to 7 GeV, both NLO QCD and the k_T-factorisation calculations are in good agreement with the data.