for the COSY-11-Collaboration
Institut für Kernphysik, Forschungszentrum Jülich, 52425 Jülich
Institute of Physics, Jagellonian University, ul. Reymonta 4, 30-059~Cracow, Poland
The production of eta meson in elementary proton-proton collisions has been investigated at the synchrotrons CELSIUS, COSY and SATURNE. The experimental data allows to establish that the dependence of the total cross section on the excess energy is predominantly determined by the final state interaction among the produced particles. In case of the pp->pp eta reaction the achieved precision permits to distinguish the effect of the eta-nucleon interaction from the overwhelming influence of the nucleon-nucleon distortion.
A modification of the phase space occupation due to the eta pp interaction is evidently seen in the high statistics exclusive measurements of the pp->pp eta reaction recently performed at the COSY-11 facility at COSY. The world available data will be interpreted in view of the production mechanism of the eta meson in the hadronic interaction and the eta-nucleon interaction. The elaborated [1,2] and new results [3,4] of the COSY-11 collaboration obtained with both the polarised and unpolarized proton beams will be discussed.
 COSY-11: J.Smyrski et al., Phys.Lett. B474 (2000) 182
 COSY-11: P.Moskal et al., Phys.Lett. B474 (2000) 416
 COSY-11: P.Winter et al., Phys.Lett. B544 (2002) 251
 COSY-11: P.Moskal et al., pi N Newsletter 16 (2002) 367