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In order to produce a neutron-rich Lambda hypernucleus for the first time, we carried out an experiment by utilizing the (pi-,K+) double charge-exchange reaction on a 10B target. We observed the production of a 10LambdaLi hypernucleus. The cross section for the Lambda bound region was found to be 11.3+/-1.9 nb/sr with the 1.2 GeV/c incident momentum, which is compared with the 10LambdaB hypernucleus production cross section, 7.8+/-0.3 microb/sr, in the (pi+,K+) reaction with a 1.05 GeV/c incident momentum beam.

The energy spacing between the ground-state spin doublet of 4 Λ He(1 + ,0 + ) was determined to be 1406 ± 2 ± 2 keV, by measuring γ rays for the 1 + → 0 + transition with a high efficiency germanium detector array in coincidence with the 4 He(K − , π − ) 4Λ He reaction at J-PARC. In comparison to the corresponding energy spacing in the mirror hypernucleus 4 Λ H, the present result clearly indicates the existence of charge symmetry breaking (CSB) in ΛN interaction. It is also found that the CSB effect is large in the 0 + ground state but is by one order of magnitude smaller in the 1 + excited state, demonstrating that the ΛN CSB interaction has spin dependence.

The present status of hypernuclear γ-ray spectroscopy with Hyperball is summarized. We observed two γ transitions of 16 Λ O(1 − → 1 − , 0 − ) and obtained the strength of the ΛN tensor force. In 10 B(K − , π − γ) data, we did not observe the spin-flip M1 transition of 10 Λ B(2 − → 1 − ), but γ rays from hyperfragments such as 7 Λ Li(7/2 + → 5/2 + ) and 9 Λ Be(3/2 + → 1/2 + ) were observed. In 11 B(π + , K + γ) data, we observed six γ transitions of 11 Λ B. We also attempted an inclusive γ-ray measurement with stopped K − beam. † Present address:

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