Near - threshold ω - meson production in proton - proton collisions ∗ : With or without resonance excitations ?

We present results for the pp → ppω reaction studied by considering two different scenarios: with and without the inclusion of nucleon resonance excitations. The recently measured angular distribution by the COSY-TOF Collaboration at an excess energy of Q = 173 MeV and the energy dependence of the total cross section data for π−p → ωn are used to calibrate the model parameters. The inclusion of nucleon resonances improves the theoretical prediction for the energy dependence of the total cross section in pp → ppω at excess energies Q < 31 MeV. However, it still underestimates the data by about a factor of two, and remains a problem in understanding the reaction mechanism.