Asymmetry in nonmesonic decay of polarized Λ5He hypernucleus

We have measured the asymmetric emission of protons and pions from the nonmesonic decay of the polarized 5LambdaHe prodiced by the (pi+, K+) reaction. 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 discrepancy can be attributed to insufficient knowledge of the weak LambdaN interaction, especially at short range, which may consistently explain the discrepancy seen in the partial decay rates of the nonmesonic decay.