Reactions pd${\to }^3$He η and pd${\to }^3$He ${\mathrm{\pi }}^{+}$${\mathrm{\pi }}^{\mathrm{-}}$ near the η threshold

The reaction pd${\to }^3$Heη has been studied with the SPES2 spectrometer, for proton energies between 0.2 MeV and 11 MeV above threshold. The total cross section rises from 0.25 to 0.40 μb in this region. The observed energy dependence can be attributed to the strong final state interaction. The angular distribution is nearly isotropic, consistent with S wave production. A measurement of the pd${\to }^3$He${\mathrm{\pi }}^{+}$ ${\mathrm{\pi }}^{\mathrm{-}}$ cross section in the threshold region is also presented. The setup, which is capable of producing ${10}^5$ tagged η/s with only a few percent background, is used to investigate rare η decays. © 1996 The American Physical Society.