Measurement of double polarisation asymmetries in ω-photoproduction

Abstract The first measurements of the beam-target-helicity-asymmetries E and G in the photoproduction of ω -mesons off protons at the CBELSA/TAPS experiment are reported. E ( G ) was measured using circularly (linearly) polarised photons and a longitudinally polarised target. E was measured over the photon energy range from close to threshold ( E γ = 1108 MeV ) to E γ = 2300 MeV and G at a single energy interval of 1108 E γ 1300 MeV . Both measurements cover the full solid angle. The observables E and G are highly sensitive to the contribution of baryon resonances, with E acting as a helicity filter in the s -channel. The new results indicate significant s -channel resonance contributions together with contributions from t -channel exchange processes. A partial wave analysis reveals strong contributions from the partial waves with spin-parity J P = 3 / 2 + , 5 / 2 + , and 3 / 2 − .