Study of Asymmetric Weak decay of Polarized Hypernuclei Produced by(K^-, pi^0)

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The purpose of this research project is to study strangeness changing weak hyperon nucleon interaction by observing asymmetric angular distibution of the nonmesonic weak decay of polarized hypernuclei. There are(pi^+, K^+)and n(K^-, pi)reactions to produce polarized hypernuclei. We showed that the n(K^-, pi)reaction introduces larger polarization to hypernuclei^1 and we planned to use it in the beginning of this project.Meanwhile new beam line and superconducting spectrometer are constructed at KEK.They made the study of hypernuclei by using the(pi^+, K^+)reaction quite effective in practice, although the use of n(K^-, pi)reaction is still good in principle. We proposed an experiment "Study of asymmetric nonmesonic weak decay of polarized LAMBDA^^5He hypernuclei" to the KEK proton synchrotron which uses(pi^+, K^+)reaction. It was approved(PS-E278)in 1992 and successfully completed at the end of 1993.The experiment is expected to give new information on the strangeness changing weak hyperon nucleon interaction. Futhermore since quality of data exceeds far the previous study, we should be able to gives new information on production, structure and weak decay of LAMBDA^^5He hypernuclei. We will spend another year to extract results out of them. Meanwhile we were carring out study of related physics and following results were obtained.1) Polarization of LAMBDA hyperons in the quasifree process (ref.3,5)2) Separation of quasifree LAMBDA production and production of hypernuclei (ref.6)3) Polarization of hypernuclei produced by the (pi^+, K^+) reaction and asymmetry nonmesonic decay (ref.2,4,7)4) Hyperon and nucleon weak interaction and weak nonmesonic decay (ref.8,9)5) Strong and weak hyperon nucleon interaction in nuclei (ref.8)