Selected Topics in Spectroscopy of -Hypernuclei and Hyperon-Nucleon Interactions

Hyperon-nucleon forces in hypernuclei, obtained from the analysis of the binding energies of a Λ hyperon and of hypernuclear spectra, are discussed. It is pointed out that the low-energy hypernuclear data obtained in the ( K −, π −) and ( π +, K +) reactions at momentum transfers q <0.4 GeV/ c bear out the baryon picture of a hypernucleus, which presumes the non-identity of a Λ hyperon and a nucleon (the shell model or cluster structure and the Pauli principle at the baryon level). Manifestation of the quark degrees of freedom is more likely in the short-range region of interaction between a hyperon and nucleons, which is responsible for the formation of quark bags, for the spin-orbit interaction and possibly for the mechanism of non-mesonic decay of hypernuclei.