The Non-Mesonic (NM) decay of $^4_Lambda{mathrm{He}}$ and $^5_Lambda{mathrm{He}}$ 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 $^4_Lambda{mathrm{He}}rightarrow d+d,; p+t$ 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 $(1.37pm 0.37)times 10^{-5}/K^-_{stop}$ and $(8.3pm 1.0)times 10^{-5}/K^-_{stop}$, respectively. Due to the capability of FINUDA of identifying $^5_Lambda{mathrm{He}}$ hypernuclei, a few $^5_Lambda{mathrm{He}}rightarrow d+t$ decay events have also been observed. The branching ratio for this decay channel has been measured for the first time: $(3.0pm 2.3)times 10^{-3}$.
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