Measurement of the proton spectra from non-mesonic weak decay of 5He-Lambda, 7Li-Lambda and 12C-Lambda

The results of a measurement of the proton spectra following the non-mesonic weak decay of Λ5He, Λ7Li and 12C are presented and discussed. The experiment was performed at the (e+ e−) collider DANE at Λ7 Laboratori Nazionale di Frascati of INFN. It is the first measurement for ΛLi, and for all the spectra the lower limit on the energy of the protons is 15 MeV, never reached before. All the spectra show a similar shape, namely a peak at around 80 MeV as expected for the free Λp → np weak reaction, with a low energy rise that should be due to final state interactions and/or two-nucleon induced weak processes. The decay spectrum of Λ5He is somehow similar to the ones reported by previous measurements and theoretical calculations, but the same does not happen for the 12C one.