Eur. Phys. J. C 6, 67-83
DOI 10.1007/s100529801017
Measurement of inclusive 
and associated dijet
cross sections
in photoproduction at HERA
The ZEUS Collaboration
J.Breitweg et al.
Argonne National Laboratory, Argonne, IL, USA
Received: 9 July 1998 / Published online: 22 October 1998
Abstract
Inclusive photoproduction of 
mesons has been measured for
photon-proton centre-of-mass energies in the range 130<W<280GeV and photon
virtuality Q2 < 1GeV2. The data sample used corresponds to an
integrated luminosity of 37 pb-1. Total and differential cross
sections as functions of the D* transverse momentum and
pseudorapidity are presented in restricted kinematical regions and the
data are compared with next-to-leading order (NLO) perturbative QCD
calculations using the "massive charm" and "massless charm'' schemes.
The measured cross sections are generally above the NLO calculations,
in particular in the forward (proton) direction. The large data
sample also allows the study of dijet production associated with
charm. A significant resolved as well as a direct photon component
contribute to the cross section. Leading order QCD Monte Carlo
calculations indicate that the resolved contribution arises from a
significant charm component in the photon. A massive charm NLO parton
level calculation yields lower cross sections compared to the measured
results in a kinematic region where the resolved photon contribution
is significant.
Copyright Springer-Verlag
