Properties of eta-meson production in nucleon-nucleon collisions near threshold

Polarization observables in eta production induced by NN collisions p+p-->p+p+eta, n+p-->n+p+eta, and n+p-->d+eta, are derived. The unique S wave spin structure of the threshold amplitude for p+p-->p+p+eta allows us to calculate all polarization observables in an universal form. Asymmetries in np collisions, characterized by noninterfering singlet and tripler amplitudes, are calculated. From the large experimental ratio of the differential cross sections of the processes n+p-->n+p+eta and p+p-->p+p+eta, near threshold, one predicts large spin correlation coefficients C-xx (C-yy). The spin structure of S- and P- wave contributions is derived.