Branching ratio of $K_S^0$ decays into ${\pi }^{+}{\pi }^{-}$ and ${\pi }^0{\pi }^0$ modes

We have measured the branching ratio $R=\frac{\Gamma (K_S^0\to {\pi }^{+}{\pi }^{-})}{\Gamma (K_S^0\to {\pi }^0{\pi }^0)}$ of $K_S^0$ produced in the reaction ${\pi }^{-}+p\to {\Lambda }^0+K^0$ in the 1.45 GeV / c ${\pi }^{-}$ beam of the Princeton-Pennsylvania Accelerator. The $K_S^0$ decay secondaries were detected in an array of magnetostrictive-readout wire spark chambers interleaved with lead and copper radiators to convert $\gamma$ rays. The position of $K^0$ production in the target was detected with a unique trigger-target apparatus allowing a correction for the background produced by $K_L^0$ decays. The branching ratio corrected for this background and other standard effects is $R=2.11\mathrm{}\pm 0.09$, in good agreement with the world average.