A coupled-channel analysis for phi-photoproduction with Lambda(1520)

Abstract

We investigate photoproduction of $ϕ$-mesons off protons within a coupled-channel effective-Lagrangian method which is based on the K-matrix approach. Since the threshold energy of the $KΛ(1520)$ channel is close to that of $ϕN$, the contribution of this channel to $ϕ$-photoproduction near the threshold energy region may give rise to some unexpected structures. In the transition amplitude $KΛ(1520) \to ϕN$, the kinematics allows an intermediate kaon to be on-shell. This happens in the energy region where a peak structure has been observed in $ϕ$-photoproduction. In our calculations the on-shell kaon effect indeed reproduces a peak structure, however, with a magnitude that is far too small to explain the observed effect. As a following step we introduce a nucleon resonance in our model. The coupling of the resonance to the $KΛ(1520)$ and $ϕN$ channels is not suppressed by the OZI rule if the resonance contains a dominant hidden strangeness component. We find that the resonance can reproduce a peak structure of the correct magnitude at the right energy. We also investigate the effects of coupled channels and the resonance on the angular distribution and the spin density matrices for $ϕ$ photoproduction.