Eur. Phys. J. C 5, 41-56
DOI 10.1007/s100529800937
Diffractive dijet cross sections in photoproduction at HERA
The ZEUS Collaboration
J. Breitweg - et al.
Argonne National Laboratory, Argonne, IL, USA
Received: 20 April 1998 / Published online: 2 July 1998
Abstract
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 (
) and pomeron (
) momentum participating
in the production of the dijet system. The observed dependence shows
evidence for the presence of a resolved- as well as a direct-photon component.
The measured cross section 
increases as 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.
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