Measurement of the Two-Photon Decay of the $K_L^0$ Meson

A measurement of the rate $\Gamma (K_L^0\to 2\gamma )$ has been made relative to the rates $\Gamma (K_L^0\to 3{\pi }^0)$, $\Gamma (K_L^0\to {\pi }^{\pm }{\mu }^{\mp }{\nu }_{\mu })$, and $\Gamma (K_L^0\to {\pi }^{\pm }{e}^{\mp }{\nu }_e)$ in a spark-chamber scintillation-counter experiment. Using published branching ratios of the three-body decays relative to the rate $\Gamma (K_L^0\to \mathrm{all})$, the branching ratio $\frac{\Gamma (K_L^0\to 2\gamma )}{\Gamma (K_L^0\to \mathrm{all})}$ has been found to be (4.5 ± 1.0) × ${10}^{-4\mathrm{}}$, based on 23 valid decays, which were separated from a small background.