Photoproduction of vector mesons off the proton at high momentum transfer

The cross-section of vector meson photoproduction at large quadri momentum transfer was measured at Jefferson Laboratory up -t = 5 GeV2. The measureme nt of the differential cross-section down to 100 pb/GeV2 was possible for t he first time thanks to the 100 % duty cycle of CEBAF in conjunction with t he large acceptance of the CLAS detector. High momentum transfer selects sm all transverse size components of both photon and hadron. In this condition hard processes (gluons: exchange) and other mechanisms like quark correlat ions may play a dominant role. Combined measurement, of Phi and rho mesons in a wide range of t will help to understand and disentangle the different contributions. So far a clear understanding of such interactions has not be en possible due to the limited amount of data and to their poor quality [1] [2]. The E93-031 experiment [3] with the CLAS detector in Hall B is coveri ng the vector-meson photo-production physics with the purpose of a precise measurement of the d sigma /dt at t < -1GeV(2)/c(2). Data have been collect ed during June '98 and July '99 runs and are now under analysis. In this contribution, preliminary results are presented for the reactions < gamma>p --> p Phi and gammap --> p rho (0) in E gamma range 3.2 - 3.8GeV.