Measurement of the invariant mass distributions for the pp → pp η ′ reaction at excess energy of Q = 16.4   MeV

The proton–proton and proton– η ′ invariant mass distributions have been determined for the pp → pp η ′ reaction at an excess energy of Q = 16.4 MeV . The measurement was carried out using the COSY-11 detector setup and the proton beam of the cooler synchrotron COSY. The shapes of the determined invariant mass distributions are similar to those of the pp → pp η reaction and reveal an enhancement for large relative proton–proton momenta. This result, together with the fact that the proton– η interaction is much stronger that the proton– η ′ interaction, excludes the hypothesis that the observed enhancement is caused by the interaction between the proton and the meson.