Hypernuclei production reactions and spectroscopy

An overview of the theoretical attainment and the recent development of the hypernuclei production by the reactions (π±, K+), (K-, π±), (γ, K+) and so on and their spectroscopy is presented. The clue to promote the nuclear physics with 'strangeness' is contemplated. The Λ-hypernuclei production experiments and recoil momentum are taken up at first, and the reaction cross section is briefly described. Experiment of 12C(π+, K+)Λ12C at KEK is the typical case of (π+, K+) reaction. The collective nature characteristic to hypernuclei observed in 9Be(π+, K+)Λ9Be at KEK SKS shows genuine hypernuclear states. Spin-orbit splitting is observed in the (π+, K+)Λ89YY reaction. The experimental hypernuclear spectra in the Quasi-Free (QF) region of the (π+, K+) reaction are well reproduced by the theoretical calculation based on the 'optimal Fermi-averaging t-matrix' approach. Exploration of Σ-hypernuclei production is reviewed. The importance and problems of the Σ-nuclear potential are discussed. In spite of numbers of experimental efforts, Σ4He is the only Σ-hypernucleus that has been found up to the present. Although the existence of the bound Σ-hypernuclei state was doubted sometimes, experimental data are theoretically reproduced finally as follows. (1) The production spectra are reproduced for all (K-, π±) reaction channels. (2) Strong Lane term and Λ-Σ coupling term as well as dispersion potential are required. (3) There exists a pole of the Σ4He unstable bound state on the second Riemann sheet of the complex energy plane, and so on. Further study subjects of the hypernuclei of the Ξ- and ΛΛ-hypernuclei, for which production of ΛΛ6He has been experimentally found as the 'Nagara event', are briefly discussed and expectation of the J-PARC experiment is mentioned. (S. Funahashi)