By means of the COSY-11 detection system , using a stochastically cooled proton beam of the Cooler synchrotron COSY  and a hydrogen cluster target , we have performed a high statistics measurement of the pp->pp eta reaction at an excess energy of Q = 15.5 MeV. The experiment was based on the four-momentum determination of both outgoing protons. This permits to identify pp->pp eta events and to derive the complete kinematical information of the eta pp-system allowing for investigations of the eta p and eta pp interactions.
At an excess energy of Q = 15.5 MeV, the final state particles remain much longer in the range of the strong interaction than the typical life-time of N* or Delta baryon resonances (10-23 s), and hence they can easily experience a mutual interaction before escaping the area of an influence of the hadronic force. This manifests itself by the modification of the phase space distribution and in particular by an enhancement of its occupation at the region where the particles have small relative momenta. Such modification of the phase space population is evidently seen in the experimental data and will be presented during the talk.
The eta-proton-proton interaction influences not only the distributions of their relative momenta, but also the magnitude of the total production cross section, which will be discussed as well.
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