An improved determination of the two--nucleon induced non mesonic weak decay of $\Lambda$-hypernuclei

TL;DR

This paper reports a precise measurement of the two-nucleon induced non-mesonic weak decay rate of $ ext{Lambda}$-hypernuclei, providing experimental evidence for the role of this mechanism in hypernuclear decay processes.

Contribution

The study presents the first direct experimental determination of the two-nucleon induced decay rate relative to total NMWD in hypernuclei, with significantly reduced uncertainty.

Findings

The ratio $ ext{Gamma}_{2N}/ ext{Gamma}_{NMWD}$ is measured as 0.24±0.03(stat)±0.03(sys).

The experimental error is reduced by more than a factor of two compared to previous estimates.

Results support the theoretical significance of two-nucleon induced decay mechanisms.

Abstract

The decay of $\Lambda$-hypernuclei without pion emission, known as Non Mesonic Weak Decay (NMWD), gives an effective tool to investigate $\Delta$S=1 four-baryon interactions. It was theoretically suggested that the two-nucleon induced mechanism could play a substantial role in reproducing the observed NMWD decay rates and nucleon spectra, but at present no direct evidence of such a mechanism has been obtained. The FINUDA experiment, exploiting the possibility to detect both charged and neutral particles coming from the hypernucleus decay, has allowed us to deduce the relative weight of the two nucleon induced decay rate to the total NMWD rate. The value of $\Gamma_{2N}$/$\Gamma_{NMWD}$=0.24$\pm$${0.03_{stat}}^{+0.03_{sys}}_{{-{0.02_{sys}}}}$ has been deduced, with an error reduced by a factor more than two compared with the previous assessment.