Beta-Decay Branching Ratio of the Lambda Hyperon

Lambda hyperons were produced by $K^{-}$ mesons at rest in the Berkeley 30-in. heavy-liquid bubble chamber filled with a mixture of 76% C${\mathrm{F}}_3$Br-24% ${\mathrm{C}}_3$ ${\mathrm{H}}_8$ by weight. A search for the $\beta$-decay mode $\Lambda \to p+e^{-}+\overline{\nu }$ was made. A total of 192 000 $\Lambda$ decays of the type $\Lambda \to p+{\pi }^{-}$ was observed. Three methods of separating the $\beta$-decay mode from the mesonic decay and from other forms of background are discussed. The most successful method of calculating the branching ratio $r=\frac{(\Lambda \to p+e^{-}+\overline{\nu })}{\left[\right(\Lambda \to p+{\pi }^{-})+(\Lambda \to n+{\pi }^0\left)\right]}$ made use of the ${\Lambda }_{\beta }$ decays identified by the electron's stopping or starting to curl up in the chamber; also, $r$ was calculated from ${\Lambda }_{\beta }$ decays in which the negative secondaries left the chamber. The nonmesonic nature of these secondaries was established either by $\delta$ rays or by decay kinematics. The values of $r$ obtained by the different methods all agree within the errors. The best value obtained is $r=(0.82\mathrm{}\pm 0.13)\times {10}^{-3\mathrm{}}$.