https://doi.org/10.1140/epjc/s10052-010-1448-6
Diffractive dijet photoproduction in ep collisions 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 and 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, TU Dortmund, Dortmund, Germany
9
Joint Institute for Nuclear Research, Dubna, Russia
10
CEA, DSM/Irfu, 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, Aix-Marseille Université, CNRS/IN2P3, Marseille, France
22
Departamento de Fisica Aplicada, CINVESTAV, Mérida, Yucatán, México
23
Departamento de Fisica, CINVESTAV IPN, México City, México
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, Université Paris-Sud, CNRS/IN2P3, Orsay, France
28
LLR, Ecole Polytechnique, CNRS/IN2P3, Palaiseau, France
29
LPNHE, Université Pierre et Marie Curie Paris 6, Université Denis Diderot Paris 7, CNRS/IN2P3, 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, Rome, 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
Received:
7
June
2010
Revised:
5
August
2010
Published online:
5
October
2010
Measurements are presented of single and double-differential dijet cross sections in diffractive photoproduction based on a data sample with an integrated luminosity of 47 pb−1. The events are of the type ep→eXY, where the hadronic system X contains at least two jets and is separated by a large rapidity gap from the system Y, which consists of a leading proton or low-mass proton excitation. The dijet cross sections are compared with QCD calculations at next-to-leading order and with a Monte Carlo model based on leading order matrix elements with parton showers. The measured cross sections are smaller than those obtained from the next-to-leading order calculations by a factor of about 0.6. This suppression factor has no significant dependence on the fraction x γ of the photon four-momentum entering the hard subprocess. Ratios of the diffractive to the inclusive dijet cross sections are measured for the first time and are compared with Monte Carlo models.
© Springer-Verlag / Società Italiana di Fisica, 2010