Photoproduction of ω mesons off the proton

Abstract

The differential cross sections and unpolarized spin-density matrix elements for the reaction p p 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 meson, 0 . 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 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 -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.