Features of $\omega$ photoproduction off nucleon target at forward angles : Dominance of $\pi$ exchange with Regge cuts and scaling of differential cross sections
We investigate photoproduction of $\omega$ off a nucleon target $\gamma N\to\omega N$ by using a Reggeized model where $\pi(135)+\sigma(500)+f_1(1285)+f_2(1270)$+Pomeron exchanges are included in the $t$-channel for the reaction at forward angles. The reaction mechanism at low energy is featured by the dominance of the $\pi$ exchange with the absorptive cuts introduced to modulate the pion contribution to both $\gamma p\to \omega p$ and $\gamma n\to \omega n$ reactions. Necessity of $\sigma$ exchange is illustrated in the analysis of the cross section from natural parity exchanges. Cross sections for differential, total, and spin density matrix with beam polarization are reproduced and compared with existing data on $\gamma p\to \omega p$. Scaled differential cross sections of Jefferson Lab data on $\gamma p\to \omega p$ are investigated at the production angle $\theta=90^\circ$ with the nonlinear trajectories for a saturation. Differential and total cross sections for the $\gamma n\to\omega n$ reaction are analyzed to compare with recent experimental data at the CBELSA/TAPS Collaboration. An application to the $\gamma p\to\omega\Delta^+$ reaction is presented to demonstrate the significance of the $\pi$ exchange in the total and differential cross sections.