Asymmetry in nonmesonic decay of polarized He-5(Lambda) hypernucleus

We have measured the asymmetric emission of protons and pions from the nonm esonic decay of the polarized He-5(Lambda) prodiced by the (pi(+), K+) reac tion. 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 theoreti cal prediction based on meson exchange model. The discrepancy can be attrib uted to insufficient knowledge of the weak Lambda N Interaction, especially at short range, which may consistently explain the discrepancy seen in the partial decay rates of the nonmesonic decay.