Measurement of diffractive photoproduction of vector mesons
large momentum transfer at HERA
The ZEUS Collaboration
J. Breitweg - et al.
Received: 16 October 1999
/ Revised version: 17 January 2000
Published online: 6 April 2000 - © Springer-Verlag 2000
Elastic and proton-dissociative photoproduction of , and vector mesons ( , , respectively) have been measured in e+pinteractions at HERA up to -t=3 GeV2, where t is the four-momentum transfer squared at the photon-vector-meson vertex. The analysis is based on a data sample in which photoproduction reactions were tagged by detection of the scattered positron in a special-purpose calorimeter. This limits the photon virtuality, Q2, to values less than 0.01 GeV2, and selects a average center-of-mass energy of = 94 GeV. Results for the differential cross sections, , for , and mesons are presented and compared to the results of recent QCD calculations. Results are also presented for the t-dependence of the pion-pair invariant-mass distribution in the mass region and of the spin-density matrix elements determined from the decay-angle distributions. The Pomeron trajectory has been derived from measurements of the W dependence of the elastic differential cross sections for both and mesons.
Copyright Società Italiana di Fisica, Springer-Verlag 2000