Nonmesonic weak decay spectra of $^4_\Lambda$He

TL;DR

This paper presents a simple theoretical model based on the shell model to analyze nonmesonic weak decay spectra of $^4_ ext{Lambda}$He, achieving good agreement with experimental data and suggesting limited importance of complex interactions.

Contribution

It introduces a straightforward phase-space-based approach using one-meson-exchange potentials to explain decay spectra, aligning well with experimental results.

Findings

Spectra shapes are mainly determined by phase space kinematics.

The model fits experimental decay rates for multiple hypernuclei.

Soft cutoff meson-exchange potentials successfully reproduce data.

Abstract

To comprehend the recent Brookhaven National Laboratory experiment E788 on $^4_\Lambda$He, we have outlined a simple theoretical framework, based on the independent-particle shell model, for the one-nucleon-induced nonmesonic weak decay spectra. Basically, the shapes of all the spectra are tailored by the kinematics of the corresponding phase space, depending very weakly on the dynamics, which is gauged here by the one-meson-exchange-potential. In spite of the straightforwardness of the approach a good agreement with data is acheived. This might be an indication that the final-state-interactions and the two-nucleon induced processes are not very important in the decay of this hypernucleus. We have also found that the $\pi+K$ exchange potential with soft vertex-form-factor cutoffs $(\Lambda_\pi \approx 0.7$ GeV, $\Lambda_K \approx 0.9$ GeV), is able to account simultaneously for the available experimental data related to $\Gamma_p$ and $\Gamma_n$ for $^4_\Lambda$H, $^4_\Lambda$He, and $^5_\Lambda$He.