Photoproduction of ω mesons off the proton

The differential cross sections and unpolarized spin-density matrix elements for the reaction γp→pωγp→pω were measured using the CBELSA/TAPS experiment for initial photon energies ranging from the reaction threshold to 2.5 GeV. These observables were measured from the radiative decay of the ω   meson, ω→π0γω→π0γ. The cross sections cover the full angular range and show the full extent of the t-channel forward rise. The overall shape of the angular distributions in the differential cross sections and unpolarized spin-density matrix elements are in fair agreement with previous data. In addition, for the first time, a beam of linearly-polarized tagged photons in the energy range from 1150 MeV to 1650 MeV was used to extract polarized spin-density matrix elements.These data were included in the Bonn–Gatchina partial wave analysis (PWA). The dominant contribution to ω   photoproduction near threshold was found to be the 3/2+3/2+ partial wave, which is primarily due to the sub-threshold N(1720)3/2+ resonance. At higher energies, pomeron-exchange was found to dominate whereas π-exchange remained small. These t  -channel contributions as well as further contributions from nucleon resonances were necessary to describe the entire dataset: the 1/2−1/2−, 3/2−3/2−, and 5/2+5/2+ partial waves were also found to contribute significantly.