AnomalousK+Decay

Abstract

Out of 5000 $K^{+}$ mesons, one has been found with a ${\pi }^{+}$ secondary of 60 Mev which exceeds the 53-Mev upper limit for the alternate tau decay mode. In view of the estimate of Dalitz, it is reasonable that this be the first observed case of the possible decay mode: $K^{+}\to {\pi }^{+}+{\pi }^0+\gamma$. There is strong evidence against the possibility that this event is a ${\tau }^{\prime }$ decay in flight, and also against the possibility that the secondary might be a ${\mu }^{+}$ rather than a ${\pi }^{+}$.