https://doi.org/10.1007/s100529800937
Experimental physics
Diffractive dijet cross sections in photoproduction at HERA
1
Argonne National Laboratory, Argonne, IL, USA
2
Andrews University, Berrien Springs, MI, USA
3
University and INFN Bologna, Bologna, Italy
6
Physikalisches Institut der Universität Bonn, Bonn, Germany
9
H.H. Wills Physics Laboratory, University of Bristol, Bristol, UK
10
Calabria University, Physics Dept.and INFN, Cosenza, Italy
11
Chonnam National University, Kwangju, Korea
14
Nevis Labs., Columbia University, Irvington on Hudson, N.Y., USA
15
Inst. of Nuclear Physics, Cracow, Poland
16
Faculty of Physics and Nuclear Techniques, Academy of Mining and Metallurgy, Cracow, Poland
17
Jagellonian Univ., Dept. of Physics, Cracow, Poland
18
Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany
25
DESY-IfH Zeuthen, Zeuthen, Germany
26
University and INFN, Florence, Italy
27
INFN, Laboratori Nazionali di Frascati, Frascati, Italy
28
Fakultät für Physik der Universität Freiburg i.Br., Freiburg i.Br., Germany
30
Dept. of Physics and Astronomy, University of Glasgow, Glasgow, UK
32
I. Institute of Exp. Physics, Hamburg University, Hamburg, Germany
33
II. Institute of Exp. Physics, Hamburg University, Hamburg, Germany
34
High Energy Nuclear Physics Group, Imperial College London, London, UK
35
Physics and Astronomy Dept., University of Iowa, Iowa City, USA
36
Forschungszentrum Jülich, Institut für Kernphysik, Jülich, Germany
37
Institute of Particle and Nuclear Studies, KEK, Tsukuba, Japan
39
Korea University, Seoul, Korea
41
Depto de Física Teórica, Univer. Autónoma Madrid, Madrid, Spain
42
Dept. of Physics, McGill University, Montréal, Québec, Canada
43
Faculty of General Education, Meiji Gakuin University, Yokohama, Japan
44
Institute of Nuclear Physics, Moscow State University, Moscow, Russia
45
NIKHEF and University of Amsterdam, Amsterdam, Netherlands
46
Physics Department, Ohio State University, Columbus, Ohio., USA
49
Department of Physics, University of Oxford, Oxford, UK
50
Dipartimento di Fisica dell’ Università and INFN, Padova, Italy
51
Dept. of Physics, Pennsylvania State University, University Park, PA, USA
52
Polytechnic University, Sagamihara, Japan
53
Dipartimento di Fisica, Univ. ‘La Sapienza’ and INFN, Rome, Italy
54
Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, UK
55
University of California, Santa Cruz, CA, USA
57
Raymond and Beverly Sackler Faculty of Exact Sciences, School of Physics, Tel-Aviv University, Tel-Aviv, Israel
58
Department of Physics, University of Tokyo, Tokyo, Japan
59
Dept. of Physics, Tokyo Metropolitan University, Tokyo, Japan
62
Dipartimento di Fisica Sperimentale and INFN, Università di Torino, Torino, Italy
63
II Faculty of Sciences, Torino University and INFN — Alessandria, Italy
64
Dept. of Physics, University of Toronto, Toronto, Ont., Canada
65
Physics and Astronomy Dept., University College London, London, UK
66
Institute of Experimental Physics, Warsaw University, Warsaw, Poland
67
Institute for Nuclear Studies, Warsaw, Poland
68
Department of Particle Physics, Weizmann Institute, Rehovot, Israel
69
Dept. of Physics, University of Wisconsin, Madison, WI, USA
70
Department of Physics, Yale University, New Haven, CT, USA
71
Dept. of Physics, York University, North York, Ont., Canada
4
IROE Florence, Italy
5
Univ. of Salerno and INFN Napoli, Italy
7
University of California, Santa Cruz, USA
13
DESY, Germany
56
University of Hamburg, Germany
Received:
20
April
1998
Published online: 15 December 1998
Differential dijet cross sections have been measured with the ZEUS detector for photoproduction events in which the hadronic final state containing the jets is separated with respect to the outgoing proton direction by a large rapidity gap. The cross section has been measured as a function of the fraction of the photon (ϰγ OBS) and pomeron (β OBS) momentum participating in the production of the dijet system. The observed ϰγ OBS dependence shows evidence for the presence of a resolved- as well as a direct-photon component. The measured cross section da/dβ OBS increases as β OBS increases indicating that there is a sizeable contribution to dijet production from those events in which a large fraction of the pomeron momentum participates in the hard scattering. These cross sections and the ZEUS measurements of the diffractive structure function can be described by calculations based on parton densities in the pomeron which evolve according to the QCD evolution equations and include a substantial hard momentum component of gluons in the pomeron.
© Springer-Verlag, 1998