Polarization observables in ω photo-production

The total cross section of ω photo-production off proton shows several bumps in the incoming photon energy range 1.1–2.5 GeV, which can be ascribed to the contribution of intermediate proton excited states in the s-channel of the reaction. At the same time, differential cross sections show a diffractive behavior, which is interpreted in terms of t-channel exchange contributions. A complete understanding of the ω photo-production process requires a simultaneous investigation of both t-channel exchange terms and s-channel contributions. The measurement of the angular distributions of omega decay products allows to extract the values of the spin-density-matrix elements (SDME) and to evaluate the contribution of natural/unnatural parity exchange terms. The use of polarized beam and/or target allows to measure polarization observables which can help to identify the intermediate proton excited states involved in the process. Results of SDME and polarization observables will be shown as an overview about ω photo-production.