Hypernuclear Fine Structure in OLambda16 and the Lambda N Tensor Interaction

We have observed two γ-ray transitions in OΛ16 from the 6.6 MeV excited 12− state to both ground-state spin-doublet members (11−,0−) by the (K−,π−γ) reaction. We have obtained the ground-state doublet spacing to be 26.4±1.6(stat)±0.5(syst)  keV and the excitation energy of the 12− state to be 6561.7±1.1(stat)±1.7(syst)  keV. The ground-state doublet spacing provides a small but nonzero strength of the tensor interaction between a Λ and a nucleon. This is the first experimental result on the ΛN tensor interaction.