Recent achievements and perspectives on strangeness nuclear physics are presented, based mainly on experimental highlights at J-PARC. Their connection to high-density matter in neutrons stars is also discussed.
A high-quality -proton scattering experiment (J-PARC E40) successfully measured differential cross sections of ±p elastic and inelastic scattering [1,2]. They provide invaluable information to develop baryon-baryon interaction models, which are necessary to construct a realistic Equation of State for high-density matter in neutron stars. The phase-shift result of the p scattering helps us understand the origin of the repulsive core of nuclear force . A high-quality p scattering experiment is also planned at J-PARC.
Through recent data from heavy ion collisions, it is recognized that the lifetime and the binding energy of the lightest hypernuclei, hypertriton (3H), should be measured reliably and precisely. Updated results have been reported from ALICE and STAR, and new measurements are on-going at J-PARC. In addition, the nn state, suggested to be bound in a GSI experiment, was searched for at JLab . Those data will play essential roles to understand behavior of a hyperon in neutron stars.
Doubly strange hypernuclei were also studied at J-PARC (E07) with a hybrid emulsion technique. Among clearly-observed hypernuclear events [3,4], two of them have surprisingly large binding energies and naively interpreted as a state with a in the nuclear 0s orbit . But this interpretation leads to extremely weak N→interaction inconsistent with theoretical predictions. A missing mass spectroscopy experiment of the (K, K) reaction for hypernuclei (E70), together with a -atomic X-ray measurement (E96), will soon clarify the situation.
In the future, further investigation of the NN three-body force is necessary to solve the “hyperon puzzle” in neutron stars, through high-resolution hypernuclear spectroscopy at JLab, and then at the extended Hadron Facility at J-PARC .
 K. Miwa et al., Phys. Rev. C 104 (2021) 045204; Phys. Rev. Lett. 128 (2022) 072501.
 T. Nanamura et al., Prog. Theor. Exp. Phys. 2022 (2022) 093D01,
 K.N. Suzuki et al., Prog. Theor. Exp. Phys. 2022 (2022) 013D01; B. Pandey et al., Phys. Rev. C 105 (2022) L051001.
 S. H. Hayakawa et al., Phys. Rev. Lett. 126 (2021) 062501.
 M. Yoshimoto et al., Prog. Theor. Exp. Phys. 2021 (2021) 7.
 K. Aoki et al., arXiv: 2110.04462 [nucl-ex] (2021).