Spectroscopy of S = -1 hypernuclei at KEK, BNL and J-PARC

The hypernuclear physics program at J-PARC will start soon. Taking this occasion, I will summarize what we have achieved in the spectroscopy of $\Lambda$ hypernuclei at KEK-PS and BNL-AGS using meson beams, where the SKS spectrometer and the Ge detector array, Hyperball, have played essential roles. The ($\pi^+$,$K^+$) reaction spectroscopy data in a wide mass range clearly demonstrated single-particle orbits of a $\Lambda$ even in a heavy nucleus and revealed properties of the $\Lambda$'s nuclear potential. Then almost full set of p-shell $\Lambda$ hypernuclear gamma-ray data provided the strengths of each of the $\Lambda$-N spin-dependent forces (spin-spin,spin-orbit, and tensor interactions). In addition, the ($\pi^-$,$K^+$) reaction was successfully introduced to observe neutron rich hypernuclei as well as to study $\Sigma$-nucleus interaction. Future perspectives at the J-PARC 50 GeV proton synchrotron are also discussed. At J-PARC, the K1.8 beam line and the SKS spectrometer are almost ready to get the first beam. We plan gamma-ray spectroscopy experiments covering a wide mass range, from $^4_{\Lambda}$He to sd-shell hypernuclei such as $^{19}_{\Lambda}$F, and then even heavier ones, using a newly-constructed Ge detector array, Hyperball-J. The ($\pi^-$,$K^+$) spectroscopy of neutron-rich hypernuclei will be also exploited. One of the physics motivations of these experiments is to investigate the three-body $\Lambda$$N$$N$ force caused by $\Sigma$$N$- $\Lambda$$N$ coupling. We also try to extend the hypernuclear chart toward the neutron drip line and to investigate possible modifications of deformation induced by a $\Lambda$. In future, more S=-1 hyperbnuclear experiments are also planned at the K1.1 beam line and the high-resolution pion beam line with the dispersion matching technique.