Experimental Search for Semileptonic Neutrino Neutral Currents

A search for the rare $K^{+}$ decay mode $K^{+}\to {\pi }^{+}\nu \overline{\nu }$ has been carried out using stopping $K^{+}$ mesons in a heavy-liquid bubble chamber. No events were found, and an upper limit on the branching ratio of this mode of 5 × ${10}^{-5\mathrm{}}$ to all $K^{+}$ decays is obtained. Comparison is made with various theories which imply the existence of neutral neutrino currents.