HADRONIC INTERACTION OF THE η MESON WITH TWO NUCLEONS

Abstract

The COSY-11 collaboration has conducted experiments aiming at the determination of the excitation function and phase-space population of the pp→ppη 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 pp→ppη and pp→ppη′ reaction allows to distinquish in the model independent way an influence originating from the proton-proton and proton-η interaction. For the comparison the full data set from experiments performed at COSY and other laboratories is used.