Experimental Test of theΔS=ΔQRule in Leptonic Decays of NeutralKMesons

We report the final results of a study of the time distribution of decays of neutral $K$ mesons produced in the reaction ${K}^{\ensuremath{-}}+p\ensuremath{\rightarrow}{\overline{K}}^{0}+n$. We present independent results based on 81 electronic and 38 muonic decays. Combining these with 133 ambiguous events, we find for the $\ensuremath{\Delta}S=\ensuremath{-}\ensuremath{\Delta}Q$ parameter $x$ the value $\mathrm{Re}(x)={{0.25}_{\ensuremath{-}0.09}}^{+0.07}$, $\mathrm{Im}(x)=0.00\ifmmode\pm\else\textpm\fi{}0.08$. This value lies about 2.5 standard deviations away from the point $x=0$, and to this extent our experiment suggests a violation of the $\ensuremath{\Delta}S=\ensuremath{\Delta}Q$ rule. In the course of an investigation of background processes, we identify and measure the rate of the radiative decay ${K}_{S}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\gamma}$.