Measurement of the Decay Rate for the Rare ProcessKL0→μ+μ−

Abstract

We have measured the decay rate for ${K_L}^0\to {\mu }^{+}{\mu }^{-}$ in a double-arm spectrometer at the Argonne zero-gradient synchrotron. Sixteen events were found, from which we calculate $\frac{\Gamma ({K_L}^0\to {\mu }^{+}{\mu }^{-})}{\Gamma ({K_L}^0\to {\pi }^{+}{\pi }^{-})}={4.2}_{-0.9\mathrm{}}^{+1.4\mathrm{}}\times {10}^{-6\mathrm{}}$.