New results on Mesonic Weak Decay of $p$-shell $\Lambda$-Hypernuclei

TL;DR

This paper reports the first measurements of negatively charged pion spectra from mesonic decay of p-shell $ ext{Lambda}$-hypernuclei, confirming and assigning spin-parity to their ground states through experimental data and theoretical comparison.

Contribution

It provides new experimental data on pion spectra from mesonic decay of p-shell hypernuclei and confirms or assigns their ground-state spin-parity.

Findings

First measurement of $ ext{pi}^-$ spectra for several p-shell hypernuclei.

Confirmed spin-parity for ${^{7}_{ ext{Lambda}}Li}$ and ${^{11}_{ ext{Lambda}}B}$.

First assignment of spin-parity for ${^{15}_{ ext{Lambda}}N}$ ground state.

Abstract

The FINUDA experiment performed a systematic study of the charged mesonic weak decay channel of $p$-shell $\Lambda$-hypernuclei. Negatively charged pion spectra from mesonic decay were measured with magnetic analysis for the first time for ${^{7}_{\Lambda}Li}$, ${^{9}_{\Lambda}Be}$, ${^{11}_{\Lambda}B}$ and ${^{15}_{\Lambda}N}$. The shape of the $\pi^{-}$ spectra was interpreted through a comparison with pion distorted wave calculations that take into account the structure of both hypernucleus and daughter nucleus. Branching ratios $\Gamma_{\pi^{-}}/\Gamma_{tot}$ were derived from the measured spectra and converted to $\pi^{-}$ decay rates $\Gamma_{\pi^{-}}$ by means of known or extrapolated total decay widths $\Gamma_{tot}$ of $p$-shell $\Lambda$-hypernuclei. Based on these measurements, the spin-parity assignment $1/2^+$ for ${^{7}_{\Lambda}Li}$ and $5/2^+$ for ${^{11}_{\Lambda}B}$ ground-state are confirmed and a spin-parity $3/2^+$ for ${^{15}_{\Lambda}N}$ ground-state is assigned for the first time.