Experimental Study of the DecayKL→π0π0and Other Rare Decay Modes

Abstract

We have measured the branching ratio $\frac{\Gamma (K_L\to 2{\pi }^0)}{\Gamma (K_L\to 3{\pi }^0)}$ to be (4.6±1.1)×${10}^{-3\mathrm{}}$. This leads to $\frac{\Gamma (K_L\to 2{\pi }^0)}{\Gamma (K_L\to \mathrm{all})}=(0.97\mathrm{}\pm 0.23)\times {10}^{-3\mathrm{}}$ and a $\mathrm{CP}$-violation parameter $\left|{\eta }_{00}\right|=(2.2\mathrm{}\pm 0.3)\times {10}^{-3\mathrm{}}$. We also report $\frac{\Gamma (K_L\to \gamma \gamma )}{\Gamma (K_L\to \mathrm{all})}=(4.7\mathrm{}\pm 0.6)\times {10}^{-4\mathrm{}}$, $\frac{\Gamma (K_S\to \gamma \gamma )}{\Gamma (K_S\to \mathrm{all})}<0.02\mathrm{}$ with 90% confidence and $\frac{\Gamma (K_L\to {\pi }^0\gamma \gamma )}{\Gamma (K_L\to \mathrm{all})}<2.3\mathrm{}\times {10}^{-4\mathrm{}}$ with 90% confidence.