Neutron and proton energy spectra from the non-mesonic weak decays of _Λ ⁵He and _Λ ¹²C

We have simultaneously measured the energy spectra of neutrons and protons emitted in the non-mesonic weak decays of _Λ ⁵He and _Λ ¹²C hypernuclei produced via the (π ⁺, K ⁺) reaction with much higher statistics than those of previous experiments. The neutron-to-proton yield ratios for both hypernuclei at a high energy threshold (60 MeV) were approximately equal to two, which suggests that the ratio of the neutron- and proton-induced decay channels, Γ _n(Λn→nn)/Γ _p(Λp→np), is about 0.5. In the neutron energy spectra, we found that the yield of the low-energy component is unexpectedly large, even for _Λ ⁵He.