Parity Nonconservation in the Decay of Free and BoundΛParticles

Abstract

A quantitative estimate is made of the branching ratio between two-body and more complicated mesonic decay modes for ${}_{\Lambda }{}^{}{}_{}{}^{}\mathrm{He}_{}^4{}_{}{}^{}$ and ${}_{\Lambda }{}^{}{}_{}{}^{}\mathrm{H}_{}^4{}_{}{}^{}$, as function of their spin $J$ and the ratio $\frac{p}{s}$ of the $s$- and $p$-channel amplitudes in free $\Lambda$ decay. Comparison with the data on ${}_{\Lambda }{}^{}{}_{}{}^{}\mathrm{H}_{}^4{}_{}{}^{}$ decay indicates that $J=1\mathrm{}$ is rather improbable and that, with $J=0\mathrm{}$, an upper limit on $\frac{p}{s}$ is about unity, a lower limit of 0.45 being obtained from the observations on up-down asymmetry in polarized $\Lambda$ decay. The theoretical and experimental values for the nonmesonic/mesonic ratio in hypernuclear decay are compared in the light of these limits on $\frac{p}{s}$. Assuming validity of the $\Delta T=\frac{1}{2}$ rule, the variations in the $\frac{{\pi }^{-}}{{\pi }^0}$ ratio for decays of light hypernuclei ($Z<~2$) due to the effect of the Pauli principle are also estimated. A brief discussion of ${}_{\Lambda }{}^{}{}_{}{}^{}\mathrm{H}_{}^3{}_{}{}^{}$ decay is given in an appendix.