2018 Impact factor 4.843
Particles and Fields
Eur. Phys. J. C 14, 213-238
DOI 10.1007/s100520000374

Measurement of diffractive photoproduction of vector mesons
at large momentum transfer at HERA

The ZEUS Collaboration

J. Breitweg - et al.

Argonne National Laboratory, Argonne, IL, USA

Received: 16 October 1999 / Revised version: 17 January 2000 /
Published online: 6 April 2000 - © Springer-Verlag 2000

Elastic and proton-dissociative photoproduction of $\rho^0$, $\phi$and $J/\psi$ vector mesons ( $\gamma p\rightarrow Vp$, $\gamma
p\rightarrow VN$, 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 $\gamma p$ average center-of-mass energy of $\langle W\rangle$ = 94 GeV. Results for the differential cross sections, ${{d}\sigma/{d}t}$, for $\rho^0$, $\phi$ and $J/\psi$ 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 $\rho^0$ 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 ${{d}\sigma/{d}t}$ for both $\rho^0$ and $\phi$ mesons.

Copyright Società Italiana di Fisica, Springer-Verlag 2000