Gamma-Ray Spectroscopy of $^{16}_\Lambda$O and $^{15}_\Lambda$N Hypernuclei via the $^{16}$O$(K^-, \pi^-)$ reaction

TL;DR

This study used gamma-ray spectroscopy to analyze the level structures of $^{16}_\Lambda$O and $^{15}_\Lambda$N hypernuclei, revealing details about the $\Lambda N$ interaction and the tensor component through experimental measurements and shell-model comparisons.

Contribution

First detailed gamma-ray spectroscopy of these hypernuclei, providing new data on $\Lambda N$ interaction and tensor force effects in hypernuclear structure.

Findings

Determined the level scheme of $^{16}_\Lambda$O from gamma-ray transitions.

Measured the lifetime of the $^{15}_\Lambda$N $1/2^+;1$ state.

Found a small but nonzero $\Lambda N$ tensor interaction strength.

Abstract

he bound-state level structures of the $^{16}_{\Lambda}$O and $^{15}_{\Lambda}$N hypernuclei were studied by $\gamma$-ray spectroscopy using a germanium detector array (Hyperball) via the $^{16}$O ($K^-, \pi^- \gamma$) reaction. A level scheme for $^{16}_{\Lambda}$O was determined from the observation of three $\gamma$-ray transitions from the doublet of states ($2^-$,$1^-$) at $\sim 6.7$ MeV to the ground-state doublet ($1^-$,$0^-$). The $^{15}_{\Lambda}$N hypernuclei were produced via proton emission from unbound states in $^{16}_{\Lambda}$O . Three $\gamma$ -rays were observed and the lifetime of the $1/2^+;1$ state in $^{15}_{\Lambda}$N was measured by the Doppler shift attenuation method. By comparing the experimental results with shell-model calculations, the spin-dependence of the $\Lambda N$ interaction is discussed. In particular, the measured $^{16}_{\Lambda}$O ground-state doublet spacing of 26.4 $\pm$ 1.6 $\pm$ 0.5 keV determines a small but nonzero strength of the $\Lambda N$ tensor interaction.