Eur. Phys. J. C (2007) 50: 283-297
https://doi.org/10.1140/epjc/s10052-007-0241-7

Regular Article - Experimental Physics

Photoproduction of events with rapidity gaps between jets 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 Universiti Malaya, Jabatan Fizik, 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, 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, Chios, 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, 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 Teorica, Universidad Autonoma 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, Ohio, 43210, USA
³⁴ Department of Physics, University of Oxford, Oxford, UK
³⁵ Dipartimento di Fisica, Universita and INFN, Padova, Italy
³⁶ Department of Physics, Pennsylvania State University, University Park, Pennsylvania, 16802, USA
³⁷ Polytechnic University, Sagamihara, Japan
³⁸ Dipartimento di Fisica, Universita “La Sapienza” and INFN, Rome, Italy
³⁹ Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, U.K.
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 Department of Physics, Tokyo Metropolitan University, Tokyo, Japan
⁴⁴ Universita di Torino and INFN, Torino, Italy
⁴⁵ Universita 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, Wisconsin, 53706, USA
⁵² Department of Physics, York University, York, Ontario, Canada M3J 1P3,
⁵³ University College London, London, UK
⁵⁴ University of Hamburg, Hamburg, Germany
⁵⁵ Univ. of Wuppertal, Wuppertal, Germany
⁵⁶ DESY group FEB, Hamburg, Germany
⁵⁷ Institut of Theoretical and Experimental Physics, Moscow, Russia
⁵⁸ INP, Cracow, Poland
⁵⁹ ICEPP, University of Tokyo, Tokyo, Japan
⁶⁰ University of Tokyo, Tokyo, Japan
⁶¹ CERN, Geneva, Switzerland
⁶² Max Planck Institute, Munich, Germany
⁶³ Department of Radiological Science, Tokyo Institute of Technology, Tokyo, Japan
⁶⁴ Lódz University, Lodz, Poland
⁶⁵ Lódz University, Lodz, Poland
⁶⁶ DESY, Hamburg, Germany

^* e-mail: gallo@mail.desy.de

Received: 4 December 2006
Revised: 23 January 2007
Published online: 20 February 2007

Abstract

The photoproduction of dijet events, where the two jets with the highest transverse energy are separated by a large gap in pseudorapidity, have been studied with the ZEUS detector using an integrated luminosity of 39 pb^-1. Rapidity-gap events are defined in terms of the energy flow between the jets, such that the total summed transverse energy in this region is less than some value E_T ^CUT. The data show a clear excess over the predictions of standard photoproduction models. This is interpreted as evidence for a strongly interacting exchange of a color-singlet object. Monte Carlo models which include such a color-singlet exchange are able to describe the data.