Polarization and weak decay of Λ hypernuclei

The 12C(π+, K+) reaction was used to produce polarized Λ hypernuclei for the first time. Asymmetries of weak decay particles were measured. In the high excitation region, where quasifree production of Λ hyperons is dominant, the polarization of Λ was derived. It is found to be consistent with that for the elementary n(π+, K+) Λ reaction which demonstrates that the spin characteristics of the elementary reaction is not modified by the nuclear medium. In the low excitation region, where hypernuclei are dominantly produced, asymmetries of the non-mesonic decay protons were measured. The measurement and calculated polarization gave large asymmetry parameter (∝ -1). It will elucidate the non-mesonic decay mechanism and open a new field of hypernuclear physics. (orig.)