Near threshold production of η, η′ and charged kaon pairs in proton-proton collisions

The near threshold production of η-and η′-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 η′ cross sections are much lower compared to π0 and π production. This observation rather excludes a resonant production of the η′-meson in the threshold region, whereas such a mechanism dominates the η 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.