Search for the rare decay $K^{+}\to {\pi }^{+}\gamma$

We have performed a search for the angular-momentum forbidden decay $K^{+}\to {\pi }^{+}\gamma$ with the E787 detector at BNL. No events were observed in the ${\pi }^{+}$ kinematic region around $227\hspace{0.5em}\mathrm{MeV}/c.\mathrm{}$ An upper limit on the branching ratio for the decay is determined to be $3.6\times {10}^{-7}$ at $90\%$ confidence level.