J. Breitweg et al., Measurement of diffractive photoproduction of vector mesons at large momentum transfer at HERA, EUR PHY J C, 14(2), 2000, pp. 213-238
Elastic and proton-dissociative photoproduction of rho(0), phi and J/psi ve
ctor mesons (gamma p --> Vp, gamma p --> VN, respectively) have been measur
ed in e(+)p interactions at HERA up to -t = 3 GeV2, where t is the four-mom
entum transfer squared at the photon-vector-meson vertex. The analysis is b
ased on a data sample in which photoproduction reactions were tagged by det
ection of the scattered positron in a special-purpose calorimeter. This lim
its the photon virtuality, Q(2), to values less than 0.01 GeV2, and selects
a gamma p average center-of-mass energy of (W) = 94 GeV. Results for the d
ifferential cross sections, d sigma/dt, for rho(0), phi and J/psi mesons ar
e presented and compared to the results of recent QCD calculations. Results
are also presented for the t-dependence of the pion-pair invariant-mass di
stribution in the rho(0) mass region and of the spin-density matrix element
s determined from the decay-angle distributions. The Pomeron trajectory has
been derived from measurements of the W dependence of the elastic differen
tial cross sections d sigma/dt for both rho(0) and phi mesons.