N. Shinkai

Asymmetric weak decay of polarized hypernuclei

We measured the asymmetric weak decay of the polarized Λ5He hypernuclei. The polarization was derived by the observed asymmetry of the mesonic decay pions for the first time. The asymmetry parameter of the nonmesonic decay has been evaluated using the obtained polarization and the asymmetry of the decay protons. The positive asymmetry parameter contradicts theoretical prediction based on meson exchange model. The present data indicates the limitation of the model in ΛN weak interaction, in particular short range phenomena such the nonmesonic decay of hypernuclei.

Study of Λ → NN process in polarized Λ5He

Abstract Strangeness changing weak hyperon nucleon interaction is studied by observing the weak nonmesonic decay (NM-decay) of Λ hypernuclei ( ΛN → NN ). Observation of its branching ratios gave spin-isospin structure of the NM-decay. Recently we carried out the experiment to observe asymmetry of protons from the weak NM-decay of the polarized Λ 5 He hypernucleus. The asymmetry is due to interference between amplitudes with different parities. It is shown that asymmetry parameter elucidates the dominant part of the NM-decay mechanism.

Spin polarization and weak decay of polarized Λ hypernuclei

Abstract Weak nonmesonic decay of Λ hypernuclei is almost unique way to study strangeness changing weak ΛN → NN process. The study of branching ratio gave spin-isospin structure of the the nonmesonic decay. A recent experiment, which observed asymmetry of protons from the polarized Λ hypernuclei, gives the interference term of amplitudes between different parities. It is shown that the asymmetry parameter elucidates the dominant part of the nonmesonic decay mechanism.