Role of nucleon resonance excitation in $\phi$ meson photoproduction

Abstract

The resonance effects are investigated in the $\phi$ meson photoproduction near threshold through a quark model approach with an effective Lagrangian. The diffractive contribution is consistently estimated by the {\it t}-channel Pomeron exchange. Another non-diffractive process, {\it t}-channel $\pi^0$ exchange is also included. The numerical result shows that the Pomeron exchange plays dominant role in the $\phi$ meson photoproduction, while the cross sections of the non-diffractive processes, i.e. {\it s}- and {\it u}-channel excitations, and {\it t}-channel $\pi^0$ exchange, are quite small. In the polarization observables, we find that large asymmetries are produced in the backward direction by the interferences from the {\it s}- and {\it u}-channel resonances, while in the forward direction, only very small asymmetries are generated. Meanwhile, we find that the effects from the $\pi^0$ exchange are generally negligible.Comment: Contribution to "2nd International Conference on Perspectives in Hadronic Physics", Trieste, ICTP, 10-14 May 1999, to appear in Few-body Syste