Search for Short-Lived Neutral Particles Emitted inK+Decay

Abstract

We have searched for the decay process $K^{+}\to {\pi }^{+}{A}^0$, where $A^0$ is any particle of mass less than 100 MeV/${\mathit{c}}^2$ decaying into $e^{+}{e}^{-}$. Upper limits for the branching ratio are given as a function of mass and lifetime of the $A^0$. For lifetimes shorter than ${10}^{-13\mathrm{}}$ sec, a limit of 4.5×${10}^{-7\mathrm{}}$ at the 90% confidence level is obtained.