Coupled-channel effects omega photoproduction near threshold

The coupled-channel effects on $\omega$ photoproduction near threshold have been investigated in a model that all relevant transition amplitudes are calculated from the tree diagrams of effective Lagrangians. With the parameters constrained by the data of $\gamma N \to \pi N$, $\gamma N\to \rho N$, and $\pi N \to \omega N$ reactions, it is found that the coupled-channel effects due to the intermediate $\pi N$ and $\rho N$ states can significantly change the differential cross sections and spin observables. Our results suggest strongly that the coupled-channel effects should be taken into account in extracting reliable resonance parameters from the data of vector meson photoproduction in the resonance region