Reactions pd-->3He eta and pd-->3He pi + pi - near the eta threshold.

Abstract

The reaction pd${\ensuremath{\rightarrow}}^{3}$He\ensuremath{\eta} 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 \ensuremath{\mu}b 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${\ensuremath{\rightarrow}}^{3}$He${\mathrm{\ensuremath{\pi}}}^{+}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$ cross section in the threshold region is also presented. The setup, which is capable of producing ${10}^{5}$ tagged \ensuremath{\eta}/s with only a few percent background, is used to investigate rare \ensuremath{\eta} decays. \textcopyright{} 1996 The American Physical Society.