Study of some two-body non-mesonic decays of ${}_{\mathrm{\Lambda }}^4$He and ${}_{\mathrm{\Lambda }}^5$He

The Non-Mesonic (NM) decay of ${}_{\mathrm{\Lambda }}^4\mathrm{H}\mathrm{e}$ and ${}_{\mathrm{\Lambda }}^5\mathrm{H}\mathrm{e}$ in two-body channels has been studied by the FINUDA Collaboration. Two-body NM decays of hypernuclei are rare and the existing observations and theoretical calculations are scarce. The ${}_{\mathrm{\Lambda }}^4\mathrm{H}\mathrm{e}\to d+d,p+t$ decay channels simultaneously observed by FINUDA on several nuclei are compared: the $pt$ channel is the dominant one. The decay yields for the two decay channels are assessed for the first time: they are $(1.37\pm 0.37)\times {10}^{-5}\mathrm{/}{K}_{stop}^{-}$ and $(8.3\pm 1.0)\times 10^{-5}/K^-_{stop}$, respectively. Due to the capability of FINUDA of identifying ${}_{\mathrm{\Lambda }}^5\mathrm{H}\mathrm{e}$ hypernuclei, a few ${}_{\mathrm{\Lambda }}^5\mathrm{H}\mathrm{e}\to d+t$ decay events have also been observed. The branching ratio for this decay channel has been measured for the first time: $(3.0\pm 2.3)\times {10}^{-3}$.