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

The spin-orbit splitting of Λ single-particle states in ¹³_ΛC was measured. The ¹³C\(K^-,π^- \)¹³_ΛC 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 ls splitting was found to be 152+/-54\(stat\)+/-36\(syst\) keV. The value is 20-30 times smaller than exhibited by the ls splitting in the nuclear shell model. This value gives us new insight into the YN interaction.