Search for the Decay ${\overline{\mathit{B}}}^0\to {\mathit{D}}^{*0\mathrm{}}\gamma$

We report results of a search for the rare radiative decay ${\overline{B}}^0\to D^{*0\mathrm{}}\gamma$. Using $9.66\times {10}^6$ $B\overline{B}$ meson pairs collected with the CLEO detector at the Cornell Electron Storage Ring, we set an upper limit on the branching ratio for this decay of $5.0\times {10}^{-5\mathrm{}}$ at 90% C.L. This provides evidence that the anomalous enhancement is absent in $W$-exchange processes and that weak radiative $B$ decays are dominated by the short-distance $b\to s\gamma$ mechanism in the standard model.