Study of the production mechanism of the eta meson in proton-proton collisions by means of analysing power measurements

The analysing power measurements for the $\vec{pp}$ → pp$\eta$ reaction studied in this dissertation are used in the determination of the reaction mechanism of the η meson production in nucleon-nucleon collisions. Measurements have been performed in the close-to-threshold energy region at beam momenta of p$_{beam}$ = 2.010 and 2.085 GeV/c, corresponding to the excess energies of Q = 10 and 36 MeV, respectively. The experiments were realised by means of a cooler synchrotron and storage ring COSY along with a cluster jet target. For registration of the reaction products the COSY-11 facility has been used. The identification of the η meson has been performed with the missing mass method. The results for the angular dependence of the analysing power combined with the hitherto determined isospin dependence of the total cross section for the η meson production in the nucleon-nucleon collisions, reveal a statistically significant indication that the excitation of the nucleon to the S$_{11}$ resonance, the process which intermediates the production of the η meson, is predominantly due to the exchange of a $\pi$ meson between the colliding nucleons. The determined values of the analysing power at both excess energies are consistent with zero implying that the η meson is produced predominantly in the s-wave at both excess energies