The production of eta-mesons in nucleon-nucleon collisions near threshold

Data on the total cross sections for the pp -> pp eta, pn -> pn eta, and pn -> d eta reactions and the pp -> pp eta differential cross section near threshold are analysed in a one-meson-exchange model. After including initial and final-state nucleon-nucleon distortion, the magnitude and most of the energy dependence are well reproduced. It is found that the contribution of rho-exchange is larger than that of pi-exchange. With destructive rho/pi interference in the pp case, the model explains quantitatively the pp -> pp eta/pn -> pn eta cross section ratio and the slope of the pp -> pp eta differential cross section. Such an agreement would be destroyed by any significant eta-exchange term. The residual energy dependence may be associated with eta-nucleon rescattering that has not been taken into account. The pn -> pn eta/pn -> d eta ratio depends weakly upon the nature of the particle exchanges, being determined primarily by the nucleon-nucleon final state interactions. The proton analysing power is predicted to remain small in the low energy region.