Measurement of the proton spectra from Non-Mesonic Weak Decay of $^5_{\Lambda}He$, $^7_{\Lambda}Li$ and $^{12}_{\Lambda}C$

TL;DR

This study measures proton spectra from non-mesonic weak decay of specific hypernuclei, revealing a common peak around 80 MeV and providing new data for $ ext{^7}_ ext{Λ} ext{Li}$ and low-energy protons.

Contribution

First measurement of proton spectra for $ ext{^7}_ ext{Λ} ext{Li}$ and for all spectra with a proton energy threshold of 15 MeV, extending previous experimental data.

Findings

Proton spectra peak at around 80 MeV consistent with free $ ext{Λ}p o np$ decay

Spectra show a low-energy rise likely due to final state interactions or two-nucleon processes

Decay spectrum of $ ext{^5}_ ext{Λ} ext{He}$ aligns with previous data, unlike $ ext{^{12}_ ext{Λ}C}$

Abstract

The results of a measurement of the proton spectra following the Non--Mesonic Weak Decay of $\mathrm{^5_{\Lambda}He}$, $\mathrm{^7_{\Lambda}Li}$ and $\mathrm{^{12}_{\Lambda}C}$ 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 $\mathrm{^7_{\Lambda}Li}$, 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 $\Lambda p \to np$ 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 $\mathrm{^5_{\Lambda}He}$ is somehow similar to the ones reported by previous measurements and theoretical calculations, but the same doesn't happen for the $\mathrm{^{12}_{\Lambda}C}$ one.