Measurement of the proton spectra from non-mesonic weak decay of Λ5He, Λ7Li and Λ12C

The results of a measurement of the proton spectra following the non-mesonic weak decay of He-5(Lambda), Li-7(Lambda) and C-12(Lambda) are presented and discussed. The experiment was performed at the (e(+) e(-)) collider DA Phi NE at Laboratori Nazionale di Frascati of INFN. It is the first measurement for Li-7(Lambda), 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 Lambda p -> 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 He-5(Lambda) is somehow similar to the ones reported by previous measurements and theoretical calculations, but the same does not happen for the C-12(Lambda) one.