We report the results of a search for the flavor-changing neutral current process $b\to d\gamma$ using a sample of $275\times {10}^6$ $B$ meson pairs accumulated by the Belle detector at KEKB. We find no significant signal for the exclusive decays $B^{-}\to {\rho }^{-}\gamma$, ${\overline{B}}^0\to {\rho }^0\gamma$, or ${\overline{B}}^0\to \omega \gamma$. Assuming an isospin relation between the three modes, we set an upper limit for the combined branching fraction $\mathcal{B}(B\to (\rho ,\omega )\gamma )$, of $1.4\times {10}^{-6}$ at the 90% confidence level. This limit can be used to constrain the ratio of CKM matrix elements $|V_{td}/V_{ts}|$.

• Received 30 May 2005

DOI:https://doi.org/10.1103/PhysRevD.72.011101