Spin physics in hypernuclei and hyperon-nucleon interactions

Role of spin in the recent study of hyperon nucleon interaction is reviewed. I discuss two phenomena. One is the spin-orbit splitting of Lambda single particle states in hypernuclei. Recently it confirmed to be very small for which gamma ray spectroscopy played an essential role. Another is the weak nonmesonic decay of Lambda hypernuclei. Spin polarization and asymmetric weak decay with respect to the polarization axis gave a new information on the study of strangeness changing weak hyperon nucleon interaction.