Off-shell ω production in proton-proton collisions near threshold -: art. no. 025202

The omega production in nucleon-nucleon collisions is described through decays of intermediate nucleon resonances. The near-threshold pp-->ppomega cross section is found to be dominated by the off-shell production of omega mesons with masses far below the physical omega mass. The N-*(1535) resonance plays thereby a crucial role. As a result of a strong Nomega coupling, this resonance leads to an off-shell contribution which is about one order of magnitude larger than the experimentally measured contribution from the omega peak. After a subtraction of the theoretical "background" from the off-shell omega 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)-->Nomega 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 pp-->ppomega cross section is substantially reduced but the description of the experimental cross section is poor above threshold.