γ-ray spectroscopy of 16ΛO and 15ΛN hypernuclei via the 16O(K-, π- γ) reaction

The 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 ∼6.7 MeV to the ground-state doublet (l - , 0 - ). The 15 Λ N hypemuclei 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 AN interaction is discussed. In particular, the measured 16 Λ O ground-state doublet spacing of 26.4 ± 1.6 ± 0.5 keV determines a small but nonzero strength of the AN tensor interaction.