Observation of Spin-Orbit Splitting in Lambda Single-Particle States

The spin-orbit splitting of {Lambda} single-particle states in {sup 13}{sub {Lambda}} C was measured. The {sup 13}C( K{sup -},{pi}{sup -}){sup 13}{sub {Lambda} }C reaction was used to excite both the 1/2{sup -} and 3/2{sup -} states simultaneously, which have predominantly {sup 12}C( 0{sup +})xp{sub {Lambda}} configuration. {gamma} rays from the states to the ground state were measured in coincidence with the {pi}{sup -} 's, by which {ell}s splitting was found to be 152{+-}54(stat){+-}36(syst )keV . The value is 20--30times smaller than exhibited by the {ell}s splitting in the nuclear shell model. This value gives us new insight into the YN interaction.