The reaction pp → ppη and the eta-nucleon and nucleon-nucleon interactions

The pi, eta and rho exchange contributions to the cross section for the reaction pp --> pp eta 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 eta -nucleon transition amplitude and die nucleon-nucleon interaction is explored. The eta -exchange mechanism is found to play a dominant role. The off-shell behavior of the etaN --> etaN amplitude within the p 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. (C) 2001 Elsevier Science B.V. All rights reserved.