The reaction pp→ppη and the eta–nucleon and nucleon–nucleon interactions Original Research Article

The π, η and ρ exchange contributions to the cross section for the reaction pp→ppη near threshold are calculated, with a phenomenological description of the intermediate S11 (N(1535)) resonance for all exchange mechanisms. The final state interaction in the pp system is described by realistic nucleon–nucleon interaction models. The sensitivity of the results to the phenomenological models for the η–nucleon transition amplitude and the nucleon–nucleon interaction is explored. The η-exchange mechanism is found to play a dominant role. The off-shell behavior of the ηN→ηN amplitude within the η exchange amplitude leads to a result significantly different from that obtained with the constant scattering length approximation. The two-nucleon amplitudes that are associated with the short-range components of the nucleon–nucleon interaction contribute significantly to the cross section.