Measurement of the proton spectra from Non-Mesonic Weak Decay of $^5_ΛHe$, $^7_ΛLi$ and $^{12}_ΛC$

Abstract

The results of a measurement of the proton spectra following the Non--Mesonic Weak Decay of $\mathrm{^5_ΛHe}$, $\mathrm{^7_ΛLi}$ and $\mathrm{^{12}_ΛC}$ are presented and discussed. The experiment was performed at the ($e^+$ $e^-$) collider DA$Φ$NE at Laboratori Nazionale di Frascati of INFN. It is the first measurement for $\mathrm{^7_ΛLi}$, 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 $Λp \to np$ 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 $\mathrm{^5_ΛHe}$ is somehow similar to the ones reported by previous measurements and theoretical calculations, but the same doesn't happen for the $\mathrm{^{12}_ΛC}$ one.