Short-lived axions and kaon decay

An experimental limit for the branching ratio $\frac{\ensuremath{\Gamma}({K}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}a)}{\ensuremath{\Gamma}({K}^{+}}\ensuremath{\rightarrow}\mathrm{all})\ensuremath{\le}1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$, where $a$ is a light, short-lived axion that decays via $a\ensuremath{\rightarrow}{e}^{+}e$, is presented.