Observation of spin-orbit splitting in Λ single-particle states

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