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

TL;DR

This study uses a coupled-channel effective-Lagrangian approach to analyze phi-meson photoproduction near threshold, revealing the importance of nucleon resonances with hidden strangeness in explaining observed peak structures.

Contribution

The paper introduces a nucleon resonance with hidden strangeness into the coupled-channel model, successfully reproducing the observed peak in phi-photoproduction.

Findings

On-shell kaon effects produce a small peak structure.

Nucleon resonance with hidden strangeness explains the peak magnitude.

Coupled-channel effects influence angular distributions and spin matrices.

Abstract

We investigate photoproduction of $\phi$-mesons off protons within a coupled-channel effective-Lagrangian method which is based on the K-matrix approach. Since the threshold energy of the $K\Lambda(1520)$ channel is close to that of $\phi N$, the contribution of this channel to $\phi$-photoproduction near the threshold energy region may give rise to some unexpected structures. In the transition amplitude $K\Lambda(1520) \to \phi N$, the kinematics allows an intermediate kaon to be on-shell. This happens in the energy region where a peak structure has been observed in $\phi$-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 $K\Lambda(1520)$ and $\phi N$ 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 $\phi$ photoproduction.