Measurement of the Up-Down Asymmetries in theβDecay of PolarizedΛHyperons (Argonne-Chicago-Ohio State-Washington University Collaboration)

We report results from a counter and optical spark-chamber-spectrometer experiment on the $\beta$ decay of polarized $\Lambda$ hyperons. A sample of 218 decays, constituting approximately one third of the total data, has been identified. The measured up-down asymmetries from a selected subsample of 173 events are $A_v=0.67\mathrm{}\pm 0.18$, $A_e=0.14\mathrm{}\pm 0.17$, and $A_p=-0.55\mathrm{}\pm 0.18$. When interpreted in the framework of a $V-A$ theory with no second-class currents ($g_2=0\mathrm{}$), they confirm the sign of the form-factor ratio $\frac{g_1}{f_1}$ as given by the Cabibbo model, but favor a somewhat smaller magnitude.