The process $\gamma p \to \phi p$ close to threshold is investigated focusing on the role played by the { \it s}- and { \it u}-channel nucleonic resonances. For this purpose, a recent quark model approach, based on the $SU(6)\otimes O(3)$ symmetry with an effective Lagrangian, is extended to the $\phi$ meson photoproduction. Another non-diffractive process, the { \it t}-channel $\pi^0$ exchange, is also included. The diffractive contribution is produced by the { \it t}-channel Pomeron exchange. Contributions from non-diffractive { \it s}- and { \it u}-channel process are found small in the case of cross sections and polarization observables at forward angles. However, backward angle polarization asymmetries show high sensitivity to this non-diffractive process. Different prescriptions to keep gauge invariance for the Pomeron exchange amplitudes are investigated. Possible deviations from the exact $SU(6)\otimes O(3)$ symmetry, due to the configuration mixing, are also discussed.
Categories: nucl-th