Experimental study of the eta-meson interaction with two-nucleons
  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-p-p-system allowing for subsequent investigations of the eta-p interaction.   The observed spectrum of the invariant mass of the proton-proton system deviates strongly from the phase-space distribution revealing the influence of the final-state-interaction among the outgoing particles or nontrivial features of the primary production mechanism. 
P. Moskal, H.-H. Adam, A. Budzanowski, R. Czyzykiewicz, D. Grzonka, M.   Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian...