Gamma-ray spectroscopy of hypernuclei - present and future

Recent results and future directions of the γ-ray spectroscopy of Λ hypernuclei are discussed. A further analysis of the last KEK experiment (E566) has revealed a new γ transition in ¹²_ΛC at 6048keV (preliminary), which is ascribed to the M1(13-→11-) transition. At J-PARC, studies will be extended from p-shell to s-shell and sd-shell hypernuclei. In the first part of the J-PARC E13 experiment, we will measure the ⁴_ΛHe(^{1 +} → ^{0 +}) transition to study charge-symmetry breaking in the ΛN interaction and investigate the ¹⁹_ΛF hypernucleus to study ΛN spin-spin interaction further using one of the sd-shell hypernuclei. In the second part of E13, we will precisely measure the spin-flip B(M1) value for the ⁷_ΛLi(3/^{2 +} → 1/^{2 +}) transition. Beyond E13, we plan to study impurity effects by observing possible changes in nuclear deformation caused by the presence of a Λ in sd-shell hypernuclei, as well as to investigate various heavier Λ hypernuclei in order to precisely determine the energies of Λ single-particle orbits.