Near Threshold Production of η, η' and Charged Kaon Pairs in Proton-Proton Collisions

The near threshold production of eta- and eta'-mesons in proton-proton collisions has been measured at excess energies up to 6.3 MeV and 25.0 MeV using the COSY-11 facility. In this region of excess energy the eta' cross sections are much lower compared to pi(0) and eta production. This observation rather excludes a resonant production of the eta'-meson in the threshold region, whereas such a mechanism dominates the eta production close to threshold. Furthermore, close to threshold data on the elementary K+K- production in the proton-proton interaction have been taken at excess energies up to 56.1 MeV.