Coupled-channel analysis for ϕ photoproduction with Λ(1520)

Abstract

We investigate photoproduction of \ensuremath{\phi} mesons off protons within a coupled-channel effective-Lagrangian method which is based on the $K$-matrix approach. Since the threshold energy of the $K\ensuremath{\Lambda}(1520)$ channel is close to that of $\ensuremath{\phi}N$, the contribution of this channel to \ensuremath{\phi} photoproduction near the threshold energy region may give rise to some unexpected structures. In the transition amplitude $K\ensuremath{\Lambda}(1520)\ensuremath{\rightarrow}\ensuremath{\phi}N$, the kinematics allows an intermediate kaon to be on-shell. This happens in the energy region where a peak structure has been observed in \ensuremath{\phi} photoproduction. In our calculations, the on-shell kaon effect indeed reproduces a peak structure, though 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 $K\ensuremath{\Lambda}(1520)$ and $\ensuremath{\phi}N$ channels is not suppressed by the Okubo-Zweig-Iizuka (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 \ensuremath{\phi} photoproduction.