Eur. Phys. J. C (2008) 55: 177-191
https://doi.org/10.1140/epjc/s10052-008-0598-2

Regular Article - Experimental Physics

Diffractive photoproduction of dijets in ep collisions at HERA

¹ Argonne National Laboratory, Argonne, Illinois, 60439-4815, USA
² Andrews University, Berrien Springs, Michigan, 49104-0380, USA
³ Institut für Physik, Humboldt-Universität zu Berlin, Berlin, Germany
⁴ University and INFN Bologna, Bologna, Italy
⁵ Physikalisches Institut, 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, New York, 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, Notkestrasse 85, 22763, Hamburg, Germany
¹⁵ Deutsches Elektronen-Synchrotron DESY, Zeuthen, Germany
¹⁶ University and INFN Florence, 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, Mytilene, Greece
²⁰ Institute of Exp. Physics, Hamburg University, Hamburg, Germany
²¹ High Energy Nuclear Physics Group, Imperial College London, London, UK
²² Institute of Particle and Nuclear Studies, KEK, Tsukuba, Japan
²³ Institute of Physics and Technology of Ministry of Education and Science of Kazakhstan, Almaty, Kazakhstan
²⁴ Institute for Nuclear Research, National Academy of Sciences, Kiev and Kiev National University, Kiev, Ukraine
²⁵ Center for High Energy Physics, Kyungpook National University, Daegu, South Korea
²⁶ Institut de Physique Nucléaire, Université Catholique de Louvain, Louvain-la-Neuve, Belgium
²⁷ Departamento de Física Teórica, Universidad Autónoma de Madrid, Madrid, Spain
²⁸ Department of Physics, McGill University, Montréal, Québec, H3A 2T8, Canada
²⁹ Faculty of General Education, Meiji Gakuin University, Yokohama, Japan
³⁰ Moscow Engineering Physics Institute, Moscow, Russia
³¹ Institute of Nuclear Physics, Moscow State University, Moscow, Russia
³² Max-Planck-Institut für Physik, München, Germany
³³ NIKHEF and University of Amsterdam, Amsterdam, Netherlands
³⁴ Physics Department, Ohio State University, Columbus, Ohio, 43210, USA
³⁵ Department of Physics, University of Oxford, Oxford, UK
³⁶ Dipartimento di Fisica, Università and INFN, Padova, Italy
³⁷ Department of Physics, Pennsylvania State University, University Park, Pennsylvania, 16802, USA
³⁸ Polytechnic University, Sagamihara, Japan
³⁹ Dipartimento di Fisica, Università ‘La Sapienza’ and INFN, Rome, Italy
⁴⁰ Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, UK
⁴¹ Raymond and Beverly Sackler Faculty of Exact Sciences, School of Physics, Tel-Aviv University, Tel-Aviv, Israel
⁴² Department of Physics, Tokyo Institute of Technology, Tokyo, Japan
⁴³ Department of Physics, University of Tokyo, Tokyo, Japan
⁴⁴ Department of Physics, Tokyo Metropolitan University, Tokyo, Japan
⁴⁵ Università di Torino and INFN, Torino, Italy
⁴⁶ Università del Piemonte Orientale, Novara, and INFN, Torino, Italy
⁴⁷ Department of Physics, University of Toronto, Toronto, Ontario, M5S 1A7, Canada
⁴⁸ Physics and Astronomy Department, University College London, London, UK
⁴⁹ Institute of Experimental Physics, Warsaw University, Warsaw, Poland
⁵⁰ Institute for Nuclear Studies, Warsaw, Poland
⁵¹ Department of Particle Physics, Weizmann Institute, Rehovot, Israel
⁵² Department of Physics, University of Wisconsin, Madison, Wisconsin, 53706, USA
⁵³ Department of Physics, York University, Ontario, M3J 1P3, Canada
⁵⁴ University College London, London, UK
⁵⁵ University of Salerno, Salerno, Italy
⁵⁶ Humboldt University, Berlin, Germany
⁵⁷ Bruker AXS, Karlsruhe, Germany
⁵⁸ Univ. Libre de Bruxelles, Bruxelles, Belgium
⁵⁹ University of Bonn, Bonn, Germany
⁶⁰ DESY group FEB, Hamburg, Germany
⁶¹ University of Liverpool, Liverpool, UK
⁶² Institut of Theoretical and Experimental Physics, Moscow, Russia
⁶³ INP, Cracow, Poland
⁶⁴ FPACS, AGH-UST, Cracow, Poland
⁶⁵ DESY, Hamburg, Germany
⁶⁶ University of Tokyo, Tokyo, Japan
⁶⁷ Kobe University, Kobe, Japan
⁶⁸ CERN, Geneva, Switzerland
⁶⁹ Max Planck Institute, Munich, Germany
⁷⁰ KEK, Tsukuba, Japan
⁷¹ Nagoya University, Nagoya, Japan
⁷² Department of Radiological Science, Tokyo Metropolitan University, Tokyo, Japan
⁷³ Łódź University, Łódź, Poland
⁷⁴ Łódź University, Łódź, Poland

^* e-mail: tobias.haas@desy.de

Received: 2 October 2007
Revised: 28 February 2008
Published online: 22 April 2008

Abstract

Diffractive photoproduction of dijets was measured with the ZEUS detector at the ep collider HERA using an integrated luminosity of 77.2 pb^-1. The measurements were made in the kinematic range Q² < 1 GeV², 0.20<y<0.85 and x_IP<0.025, where Q² is the photon virtuality, y is the inelasticity and x_IP is the fraction of the proton momentum taken by the diffractive exchange. The two jets with the highest transverse energy, E_T ^jet, were required to satisfy E_T ^jet>7.5 and 6.5 GeV, respectively, and to lie in the pseudorapidity range -1.5<η^jet<1.5. Differential cross sections were compared to perturbative QCD calculations using available parameterisations of diffractive parton distributions of the proton.