It is shown that the striking energy variation in the p d → 3 He η cross section near threshold is probably due to a final state interaction associated with a large (complex) η − 3 He scattering length. The consequences of this hypothesis are studied for the production of the meson in the η − 4 He and η − 7 Be channels.PACS number(s): 25.40. Ve, 25.10.+s

Data on the total cross sections for the pp ! ppZ, pn ! pnZ, and pn ! dZ reactions and the pp ! ppZ di¡erential cross section near threshold are analysed in a one-meson-exchange model. After including initial and ¢nal-state nucleon^nucleon distortion, the magnitude and most of the energy dependence are well reproduced. It is found that the contribution of r-exchange is larger than that of p-exchange.With destructive r/p interference in the pp case, the model explains quantitatively the pp ! ppZ/pn ! pnZ cross section ratio and the slope of the pp ! ppZ di¡erential cross section. Such an agreement would be destroyed by any signi¢cant Z-exchange term. The residual energy dependence may be associated with Z-nucleon rescattering that has not been taken into account. The pn ! pnZ/pn ! dZ ratio depends weakly upon the nature of the particle exchanges, being determined primarily by the nucleon^nucleon ¢nal state interactions. The proton analysing power is predicted to remain small in the low energy region.*

From the interactions of a deuteron beam in a liquid-hydrogen target at energies near the d+p-+ 3 He + 77 threshold, r? events were selected on the basis of the momentum-analyzed 3 He with a background of less than 2%. This opens the way to a 3 He-tagged r\ beam at Saturne, with a possible flux of 10 4 -10 5 77' s per pulse. The present data allow an evaluation of the cross section down to less than 0.5 MeV above threshold. The deuteron tensor analyzing power f 20 has also been measured: The small negative value found at threshold (-0.15 ±0.05) seems incompatible with models based on one-pion exchange.

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