Akademia Gorniczo-Hutnicza, Diss., 1999; 52 pp., (1999). doi:10.3204/DESY-THESIS-1999-045, This thesis reports on a study of elastic and proton-dissociative production of $p^O, \phi$, and $J/\psi$ vector mesons ($ep\to eVp, ep \to eV N$) at the positron-proton collider HERA. The data used for this analysis were collected by the ZEUS experiment during 1995 and correspond to an integrated luminosity of 1.98 $pb^{-1}$. The data cover the kinematic range 85 < W < 10,5 GeY and $Q^2$ < 0.01 $GeV^2$ where W and $Q^2$ are the virtual photon-proton center of mass energy and the squared four-momentum transferred by the photon. The low values of $Q^2$ covered made it possible to precisely reconstruct the four-momentum transfer squared at the photon-vector meson vertex (t) and to extract from the data the cross sections for real photoproduction of vector mesons ($\gamma p \to Vp, \gamma p \to VN$) up to -t = 3 $GeV^{2}$. In the case of $p^O$ ($p^0 \to \pi^{+} \pi^{-}$) production, the $\pi^{+} \pi^{-}$ invariant mass distribution has been investigated as a function of t. The spectra show deviations from a simple relativistic Breit- 'Vigner shape as expected in models in which the asymmetry of the $\pi{+}\pi^{-}$ invariant mass shape is ascribed to the interference of resonant and non-resonant $\pi^{+}\pi^{-}$ production. The asymmetry of the $p^O$ mass shape decreases with increasing -t. The spin density matrix elements obtained from the decay angular distribution of $p^O, \phi$ and $J/\psi$ mesons are generally consistent with expectations based on s-channel helicity conservation, except for the highest -t range accessible in this analysis where $r^{04}_{1-1}$ was found to be different from zero for all mesons. However present accuracy does not allow to conclude about SCHC violation. The differential cross sections dO'/ dt for elastic and proton-dissociative $p^{O}, \phi$ and $J/\psi$ production have been measured and compared to predictions of QCD models. The proton-dissociative cross sections at -t > 1 $GeV^{2}$ could be successfully described by QCD models. However for $p^{O}$ and $\phi$ meson photoproduction the non-perturbative mechanisms still dominate in the considered kinematical range. The ratio of elastic to proton-dissociative cross sections decreases with increasing -t for all three vector mesons in a similar way thus confirming the Regge factorization hypothesis. The ratios of $\phi$ to $p^O$ and $J/\phi$ to $p^O$ photoproduction cross sections were studied as a function of t for both elastic and proton-dissociative processes. The ratios are lower than the expected ones assuming flavour independent interactions. The Pomeron trajectory has been determined from the study of the W dependence of dO'/ dt at fixed t for $p^O$ and $\phi$ mesons in the range 0.0 < -t < 0.9 $GeV^{2}$ and 0.0 < -t < 1.4 $GeV^2$ respectively. From elastic $p^O$ photoproduction the result is $\alpha_{IP}(t)$ = ($1.08 \pm 0.02$) + ($0.11 \pm 0.04$)t and from that of $\phi$ data $\alpha _{IP}(t)$ = ($1.08 \pm 0.01$) + ($0.15 \pm 0.04$)t.