Production of η and η′ mesons via the quasi‐free proton‐neutron interaction

A comparison of the close‐to‐threshold total cross sections for the η′ meson production in both the pp → ppη′ and pn → pnη′ reactions should provide insight into the flavour‐singlet (perhaps also into gluonium) content of the η′ meson and the relevance of quark‐gluon or hadronic degrees of freedom in the creation process. The excitation function for the reaction pp → ppη′ has been already established. At present, experimental investigations of the quasi‐free pn → pnX reactions are carried out at the COSY‐11 facility using a beam of stochastically cooled protons and the deuteron cluster target. A method of measurement and preliminary results from the test experiments of the pn → pnη reaction are presented in this report.