Measurement of theKSBranching Ratio

A precise measurement of the $K_S$ branching ratio was obtained from an exposure of the 30-inch bubble chamber, filled with deuterium, to a 600-MeV/c $K^{+}$ beam at the Brookhaven AGS. Approximately 30 000 events, corresponding to the reaction $K^{+}+d\to K^0+p+p$, where both protons stopped in the bubble chamber, were found and processed. Based upon a final sample of 16475 events which passed the various selection criteria, we find that $\frac{\Gamma (K_S\to {\pi }^{+}+{\pi }^{-})}{\Gamma (K_S\to {\pi }^0+{\pi }^0)}=2.16\mathrm{}\pm 0.08$.