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

The spin-orbit splitting of Λ single-particle states in _Λ¹³C was measured. The ¹³C(K^-,π^-)_Λ¹³C reaction was used to excite both the 1/2^- and 3/2^- states simultaneously, which have predominantly ¹²C(0⁺)×p_Λ configuration. γ rays from the states to the ground state were measured in coincidence with the π^-'s, by which s splitting was found to be 152±54(stat)±36(syst)keV. The value is 20--30 times smaller than exhibited by the s splitting in the nuclear shell model. This value gives us new insight into the YN interaction.