Search for the Rare Decay ${\mathit{W}}^{\pm }\to {\pi }^{\pm }+\gamma$

We have searched for the rare decay $W^{\pm }\to {\pi }^{\pm }+\gamma$ in 16.7 $\mathrm{pb}{}^{-1\mathrm{}}$ of data taken in proton-antiproton collisions at $\sqrt{s}=1.8\mathrm{}$ TeV with the CDF detector at Fermilab. We find one event consistent with the expected signal, and estimate the background to be $2.6\pm 1.0\left(\mathrm{stat}\right)\pm 1.3\left(\mathrm{syst}\right)$ events. Without background subtraction, we find the ratio of partial widths to be $\gamma (W^{\pm }\to {\pi }^{\pm }+\gamma )/\gamma (W^{\pm }\to e^{\pm }+\nu )\le 2.0\times {10}^{-3\mathrm{}}$ at the 95% confidence level.