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We report on new measurements of the beam asymmetry for \omega\photo-production on proton and neutron in Hydrogen and Deuterium targets fromthe GRAAL collaboration. The beam asymmetry values are extracted from thereaction threshold (E_{\gamma} = 1.1 GeV in the free nucleon kinematics) up to1.5 GeV of incoming photon energy. For the first time both the radiative andthe three-pion decay channels are simultaneously investigated on the freeproton. Results from the two decay channels are in agreement and provideimportant constraints for the determination of resonant state contributions tothe \omega\ production mechanism. First experimental results on the deuteronallow the extraction of the \Sigma\ beam asymmetry on quasi-free nucleons.Comparison of the results for free and quasi-free kinematics on the protonshows a generally reasonable agreement, similar to the findings inpseudo-scalar meson photo-production reactions. For the first time measurementson quasi-free neutrons are available, showing that both the strength and theangular distributions of the beam asymmetry are sensibly different from theresults on the proton target.

Measurement of the \Sigma\ beam asymmetry for the \omega\ photo-production off the proton and the neutron at GRAAL