Off-shellωproduction in proton-proton collisions near threshold

The ω production in nucleon-nucleon collisions is described through decays of intermediate nucleon resonances. The near-threshold p→pppω cross section is found to be dominated by the off-shell production of ω mesons with masses far below the physical ω mass. The N*(1535) resonance plays thereby a crucial role. As a result of a strong Nω coupling, this resonance leads to an off-shell contribution which is about one order of magnitude larger than the experimentally measured contribution from the ω peak. After a subtraction of the theoretical ``background'' from the off-shell ω production, the available data are accurately reproduced over the entire energy range from 5 MeV up to several GeV above the threshold. The scenario of a weaker N*(1535)→Nω decay mode which is still consistent with electro- and photoproduction data is discussed as well. In the latter case, the off-shell contribution to the p→pppω cross section is substantially reduced but the description of the experimental cross section is poor above threshold.