Search for the Rare Decay W+/- -->π+/-+γ

We have searched for the rare decay ${W}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}+\ensuremath{\gamma}$ in 16.7 $\mathrm{pb}{}^{\ensuremath{-}1}$ of data taken in proton-antiproton collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8$ TeV with the CDF detector at Fermilab. We find one event consistent with the expected signal, and estimate the background to be $2.6\ifmmode\pm\else\textpm\fi{}1.0(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}1.3(\mathrm{syst})$ events. Without background subtraction, we find the ratio of partial widths to be $\ensuremath{\gamma}({W}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}+\ensuremath{\gamma})/\ensuremath{\gamma}({W}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{e}^{\ifmmode\pm\else\textpm\fi{}}+\ensuremath{\nu})\ensuremath{\le}2.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ at the 95% confidence level.