Photoproduction of ω Mesons and π⁰ω Meson Pairs off the Free Proton

The photoproduction of ω mesons and π0 ω meson pairs is studied with the intention of providing data which will be useful in isolating baryon resonances. The data used for this analysis was recorded using the CBELSA/TAPS experiment in Bonn, Germany during October-November 2002. This experiment used photons incident upon free (unbound) protons, which were contained in a liquid hydrogen target. The differential cross sections for gamma p → p ω reaction are presented for the first time by analyzing the ω meson in its radiative decay. The differential cross sections for the gamma p → p π0 ω are also presented for the first time with enough statistics and resolution to isolate baryon resonances. The initial photon energies range from threshold for each reaction to 2.5 GeV. These data show the full kinematic range of the differential cross sections for both reactions. In addition to the differential cross sections, the spin-density matrix elements have been extracted for the gamma p → p ω reaction. The unpolarized spin-density matrix elements are presented from threshold up to 2.5 GeV in initial photon energy and show remarkable agreement with previous analyses over a large angular range. Unpolarized measurements in the very forward direction are, for the first time, presented with a resolution useful for isolating baryon resonances. Also, the polarized spin-density matrix elements, ρ100 and ρ111 , are reported for the first time. These polarized elements were reported from threshold up to 1.7 GeV in initial photon energy. These spin-density matrix elements indicate the relative rate at which ω mesons are produced with a certain spin projection and will be useful in learning about the spin dynamics of the intermediate processes and any contributing baryon resonances.