Photoproduction of ω Mesons off the Proton

Abstract

The differential cross sections and unpolarized spin-density matrix elements for the reaction ${\hat{I}}^{3}p\to p\ddot{I}‰$ 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 $\ddot{I}‰$ meson, $\ddot{I}‰\to \ddot{I}{€}^0{\hat{I}}^3$. 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 $\ddot{I}‰$ 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 $\ddot{I}€$-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.

8 pages, 5 figures, accepted for publication in Physics Letters B