Neutron Energy Spectra From The Nonmesonic Weak Decay Of C-12(Lambda) And Y-89(Lambda) Hypernuclei

We have measured the neutron spectra emitted in the weak decay of C-12(Lambda) and Y-89(Lambda) over the energy region above 10 MeV in the (pi(+), K+) reaction with better statistics and an improved signal-to-background ratio. The neutron yields in the nonmesonic weak decays were obtained from the spectra. By using the proton yield of C-12(Lambda), the Gamma(n)/Gamma(p) ratio was estimated to be 0.51+/-0.15 (stat) from the neutron-to-proton yield ratio for the first time, which suggests the Gamma(n)/Gamma(p) ratio is significantly less than unity.