Isospin dependence of the eta meson production in nucleon--nucleon collisions

According to the quark model, the masses of eta and eta mesons should be almost equal. However, the empirical values of these masses differ by more than the factor of two. Similarly, though the almost the same quark-antiquark content, the total cross section for the creation of these mesons close to the kinematical thresholds in the pp --> ppX reaction differs significantly. Using the COSY-11 detection setup we intend to determine whether this difference will also be so significant in the case of the production of these mesons in the proton-neutron scattering. Additionally, the comparison of the pp --> pp eta and pn --> pn eta total cross sections will allow to learn about the production of the eta meson in the channels of isospin I = 0 and I = 1 and to investigate aspects of the gluonium component of the eta meson.