Gamma-Ray Spectroscopy of $^{16}_Λ$O and $^{15}_Λ$N Hypernuclei via the $^{16}$O$(K^-, π^-)$ reaction

Abstract

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

22 pages, 17 figures