Production of $\omega$-mesons in proton-proton collisions
  The production of $\omega$-mesons in proton-proton collisions for proton incident energies up to 2.2 GeV is investigated within a meson-exchange model of hadronic interactions.   We find a large cancellation between the dominant $\pi\rho\omega$ meson-exchange current and nucleonic current contributions. A comparison with preliminary data from SATURNE calls for the inclusion of off-shell form factors at the $NN\omega$ and $\pi\rho\omega$ production vertices. Due to the present lack of knowledge of these form factors, together with the destructive interference mentioned above, the relative magnitude of the nucleonic and meson-exchange current contributions cannot be determined from existing total cross section data. However, it is shown that the angular distribution of the produced $\omega$-mesons provides an unique and clear signature of the magnitude of these currents, thus allowing one to disentangle these two basic reaction mechanisms. 
K. Nakayama, A. Szczurek, C. Hanhart, J. Haidenbauer, and J. Speth