The Reaction pp → ppη and the eta - Nucleon and Nucleon - Nucleon Interactions

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.