Photoproduction of ω mesons off the proton

Abstract The differential cross sections and unpolarized spin-density matrix elements for the reaction γ p → p ω 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 → π 0 γ . 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 + 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 − , 3 / 2 − , and 5 / 2 + partial waves were also found to contribute significantly.