Formation of A=12 Sigma - hypernucleus from K- absorption at rest; Observation of a Sigma - spin-orbit doublet of narrow widths.

High-resolution spectroscopy of ..pi../sup +/ from K/sup -/ absorption at rest has been used for the first time to identify ..sigma../sup -/ hypernuclear states. The observed spectrum from a (CH)/sub n/ target has revealed a p/sub 3/2/-p/sub 1/2/ doublet of /sup 12/Be with narrow widths. The spin-orbit splitting of ..sigma../sup -/ is deduced to be 5 MeV, 0.8 times that for nucleons.