Observation of the Dalitz Decay Modes of theKL0

Abstract

Using a proportional-chamber spectrometer and an array of lead-glass photon detectors, we have observed four examples of the decay ${K_L}^0\to e^{+}{e}^{-}\gamma$, and one candidate for ${K_L}^0\to {\mu }^{+}{\mu }^{-}\gamma$. The corresponding branching ratios are (17.4±8.7)×${10}^{-6\mathrm{}}$ and (2.8±2.8)×${10}^{-7\mathrm{}}$, respectively. In addition we have established 90%-confidence-level upper limits of $b({K_L}^0\to e^{+}{e}^{-}{\pi }^0)<\mathrm{}2.3\mathrm{}\times {10}^{-6\mathrm{}}$ and $b({K_L}^0\to {\mu }^{+}{\mu }^{-}{\pi }^0)<\mathrm{}1.2\mathrm{}\times {10}^{-6\mathrm{}}$.