Search for the Rare Radiative Decay: $W\rightarrow\pi\gamma$ in \ppbar\   Collisions at $\sqrt{s} = 1.96$ TeV
  We present a search for the rare radiative decay \wpigamma\ using data corresponding to an integrated luminosity of 4.3 \invfb\ of proton-antiproton collisions at a center of mass energy of 1.96 TeV collected by the CDF experiment at Fermilab. As no statistically significant signal is observed, we set a 95% confidence level upper limit on the relative branching fraction \bratio\ at $6.4\times 10^{-5}$, a factor of 10 improvement over the previous limit. 
CDF collaboration, T. Aaltonen, et al
hep-ex