Hadronic interaction of η and η' mesons with nucleons

Due to their short life-time, flavour-neutral mesons cannot be utilized as free secondary beams or targets, and therefore a study of their interaction with nucleons is not possible via direct scattering experiments. It is, however, accessible via its influence on the energy dependence -- and on the phase space distributions of the cross sections for reactions in which these mesons are produced. In case of the pp → ppη reaction the experimentally determined distributions of the differential cross sections close to the production threshold cannot be described by taking into account the S-wave proton-proton and proton-η interaction only. Here we show that the angular distributions determined at the COSY-11 facility reveal some evidence for P-wave admixture in the proton-proton subsystem already at an excess energy as low as Q = 15.5 MeV. We also present that one can estimate the relative strength of the η-nucleon and η'-nucleon interactions by comparison of the η and η' production yield