Photoproduction of ω mesons off the proton

The differential cross sections and unpolarized spin-density matrix elements for the reaction γp→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→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

Data on Is and Ic in γ→p→pπ0π0 reveal cascade decays of N(1900) via N(1520)π

Photoproduction of two neutral pions off the proton is studied using linearly polarized photons, and the polarization observables Is and Ic are measured for the first time. These two observables are unique to multi-meson final states; they characterize correlations between the linear photon polarization and the direction of outgoing single particles in photoproduction of three-body final states. The Is and Ic distributions suggest that, in the 1.8 to 2.0 GeV mass region, the N(1520)3/2−π intermediate state is reached with reaction dynamics consistent with a dominant JP=3/2+ wave. These data are included in the Bonn–Gatchina (BnGa) partial wave analysis which is based on a large variety of data; the analysis confirms a significant contribution from the reaction chain γp→N(1900)3/2+→N(1520)3/2−π0→pπ0π0