Detecting hyperphotons in kaon decays

It is shown that the decay mode $K_L\to {\pi }^{+}{\pi }^{-}+\mathrm{missing}\mathrm{neutrals}$ may provide an almost model-independent limit on the parameters of the quantum ${\gamma }_Y$ of the putative fifth force. This would reduce theoretical ambiguities which arise in previous analyses of data from $K^{\pm }\to {\pi }^{\pm }+\mathrm{missing}\mathrm{neutrals}$.