New Measurement of theKLo→π+π−Branching Ratio

We have measured the ratio $\frac{\Gamma ({K_L}^0\to {\pi }^{+}{\pi }^{-})}{\Gamma ({K_L}^0\to \mathrm{a}\mathrm{l}\mathrm{l}\mathrm{c}\mathrm{h}\mathrm{a}\mathrm{r}\mathrm{g}\mathrm{e}\mathrm{d})}$ to be (2.64 ± 0.09) × ${10}^{-3\mathrm{}}$, a value significantly higher than the current accepted world average of (2.00 ± 0.07) × ${10}^{-3\mathrm{}}$. This ratio, together with currently accepted values for the ${K_S}^0\to 2\pi$ branching ratio and ${K_{L,S}}^0$ lifetimes, yields a value of $\left|{\eta }_{+-}\right|=(2.23\mathrm{}\pm 0.05)\times {10}^{-3\mathrm{}}$.