The ⌳ 13 C hypernucleus was studied by measuring ␥ rays in coincidence with the 13 C(K Ϫ , Ϫ ) reaction. ␥ rays from the 1/2 Ϫ and 3/2 Ϫ states, which are the partners of the spin-orbit doublet states with a predominant configuration of ͓ 12 C g.s. (0 ϩ ) p ⌳ ͔, to the ground state were measured. The splitting of the states was found to be ⌬E(1/2 Ϫ Ϫ3/2 Ϫ )ϭϩ152Ϯ54(stat)Ϯ36(syst) keV. This value is 20-30 times smaller than that of single particle states in nuclei around this mass region. The j ⌳ ϭl ⌳ Ϫ1/2͓(p 1/2 ) ⌳ ͔ state appeared higher in energy, as in normal nuclei. The value gives new insight into the Y N interaction. The excitation energies of the 1/2 Ϫ and 3/2 Ϫ states were obtained as 10.982Ϯ0.031(stat)Ϯ0.056(syst) and 10.830Ϯ0.031(stat)Ϯ0.056(syst) MeV, respectively. We also observed ␥ rays from the 3/2 ϩ state, which has a ͓ 12 C(2 ϩ ) s ⌳ ͔ configuration, to the ground state in ⌳ 13 C. The excitation energy of the 3/2 ϩ state was obtained as 4.880Ϯ0.010(stat) Ϯ0.017(syst) MeV. Nuclear ␥ rays with energies of 4.438 and 15.100 MeV had similar yields, which suggests that a quasifree knockout of a ⌳ particle is dominant in highly excited regions.

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An experiment demonstrating the production of double-Lambda hypernuclei in (K(-),K(+)) reactions on (9)Be was carried out at the D6 line in the BNL alternating-gradient synchrotron. The technique was the observation of pions produced in sequential mesonic weak decay, each pion associated with one unit of strangeness change. The results indicate the production of a significant number of the double hypernucleus (4)(double Lambda)H and the twin hypernuclei (4)(Lambda)H and (3)(Lambda)H. The relevant decay chains are discussed and a simple model of the production mechanism is presented. An implication of this experiment is that the existence of an S = -2 dibaryon more than a few MeV below the double Lambda mass is unlikely.

The spin-orbit splitting of Lambda single-particle states in (13)(Lambda)C was measured. The 13C(K-,pi(-))(13)(Lambda)C reaction was used to excite both the 1/2(-) and 3/2(-) states simultaneously, which have predominantly 12C(0(+)) x p(Lambda) configuration. gamma rays from the states to the ground state were measured in coincidence with the pi(-)'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.

With a germanium detector array (Hyperball), we observed two gamma-ray peaks corresponding to the two transitions (5/2(+)-->1/2(+) and 3/2(+)-->1/2(+)) in the (9)(Lambda)Be hypernucleus which was produced by the 9Be(K-,pi(-)) reaction. The energies of the gamma rays are 3029 +/- 2 +/- 1 keV and 3060 +/- 2 +/- 1 keV. The energy difference was measured to be 31.4(+2.5)(-3.6) keV, which indicates a very small Lambda-spin-dependent spin-orbit force between a Lambda and a nucleon. This is the smallest level splitting by far ever measured in a hypernucleus.