Coupled-channel analysis of the $\omega$-meson production in $\pi N$ and $\gamma N$ reactions for c.m. energies up to 2 GeV

Abstract

The pion- and photon induced reactions for the final states $\gamma N$, $\pi N$, $2\pi N$, $\eta N$, and $\omega N$ are studied within a coupled-channel effective Lagrangian approach in the energy region from the pion threshold up to 2 GeV. To investigate the role of the nucleon resonances in the different reactions we include all known states with spin-$\foh$,-$\fth$, and -$\ffh$ and masses below 2 GeV. We find a strong contribution from the $D_{15}(1675)$ resonance to the $\pi N \to \omega N$ reaction. While the $F_{15}(1680)$ state only slightly influences the $\omega $ meson production in the $\pi N$ scattering its role is enhanced in the $\omega$ photoproduction due to the large electromagnetic coupling of this resonance. We predict the beam asymmetry $\Sigma_X$ to be a negative in the $\gamma p \to \omega p$ reaction near to the threshold. Above the 1.85 GeV the asymmetry is found to change its sign and becomes positive at forward directions. The presented findings can be experimentally tested at GRAAL, CLAS, and CB-ELSA facilities.