Photoproduction of heavy vector mesons at HERA - a test field for diffraction

Exclusive diffractive photoproduction of heavy vector mesons (V=φ,J/ψ, and Υ) at HERA is studied in a model employing a dipole pomeron exchange (P) with an inelastic γPV vertex. The model is fitted to the data on dσ/dt, B, and σel for Q2=0 and beyond the threshold region. The elastic cross sections for both φ and J/ψ photoproduction show a moderate increase within the HERA energy region. The flattening of the slope B(s) (indicating little or no shrinkage) for J/ψ is not correlated with the slope of the pomeron trajectory. Estimates for Υ photoproduction at HERA are given. (orig.)