  The COSY-11 collaboration has conducted experiments aiming at the
determination of the excitation function and phase-space population of the p p
--> p p eta reaction close to the kinematical threshold. The precise data
obtained with the stochastically cooled proton beam of the cooler synchrotron
COSY and the high resolution zero-degree magnetic spectrometer allowed for the
observation of the significant deviations - in the shape of the excitation
function and two-particle invariant masses - from the predictions based on the
assumption that the reaction phase space is homogenously populated. Comparison
of the shape of the excitation function for the p p --> p p eta and p p --> p p
eta-prime reaction allows to distinquish in the model independent way an
influence originating from the proton-proton and proton-eta interaction. For
the comparison the full data set from experiments performed at COSY and other
laboratories is used.
