| The central aim of this thesis has been the measurement of the elastic process ep → eJ/psip, studied through the electronic decay in the photoproduction regime over a larger energy range than attained in previous measurements. This has been achieved by the development of a new trigger algorithm, the calibration of the ZEUS calorimeter in a dynamic range unexplored before, and extensive detector and background studies. Results have been obtained with data collected during the 1999 and 2000 running periods. The accuracy of these results largely overshoots that of previous measurements and allow us to draw two main conclusions: data are consistent with no saturation, the photoproduction of J/psi is driven by a mixture of "hard" and "soft" physics. The cross-section ratio, sigma(psi(2 S))/sigma(J/psi), has been calculated using the electron decay channel and is consistent with the suppression of the production of psi(2S) with respect to that of the J/psi, as expected by the quark parton model. Results of the search for Upsilon resonances using the electron decay channel with data taken during the 1996-2000 running periods have been reported. No clear evidence of Upsilon resonances has been found. An overview of VM production at HERA has shown that Q 2 + M2V is a good choice of the scale of the interaction. Data indicate that the dynamics that drive the increase with energy of the total DIS and VM cross-sections are similar. |
