Present stage of hypernuclear experiments

A review of hypernuclear research since its acceleration triggered by the discovery of a new double hypernucleus at KEK-E176 and inspired by Akaishi's proposal to study Ξ- + α → ΛΛ4H+n based on the idea to produce as many double hypernuclei as possible with whatever means. In spite of numbers of problems encountered ΛΛ6He was discovered (NAGARA event) in emulsion at E373 as the uniquely identified hypernuclear event, and weakly attractive ΛΛ interaction was established. On the other hand, counter experiment expecting ΛΛ5He and ΛΛ6He were performed at BNL-E906, which lead to find out two π-'s from ΛΛ4H → Λ4He*+π-, Λ4He* → p+Λ3H, Λ3H → π- + 3He in place of the expected hypernuclei. Further experiments are supposed to be performed at BNL and J-PARK in future. Concerning the weak decays of hypernuclei, recent experimental development at KEK to resolve the controversial issue of the discrepancy between theories and experiments of the nonmesonic weak decay (NMWD) is briefly explained. Development of mesonic decay studies is also explained briefly. Some results of the γ-spectroscopy, which became available and powerful to observe spin dependent fine structures, are depicted. Finally the recent work to resolve the overbinding problem by introducing coherent ΛΣ potential by Akaishi is mentioned in relation to the development of neutron star research and experimental expectations to study neutron-excess hypernuclei. (S. Funahashi)