We report new measurements of the decays $B^{+}\to {\rho }^{+}\gamma$, $B^0\to {\rho }^0\gamma$, and $B^0\to \omega \gamma$ using a data sample of $657\times {10}^6$ $B$ meson pairs accumulated with the Belle detector at the KEKB $e^{+}{e}^{-}$ collider. We measure branching fractions $\mathcal{B}(B^{+}\to {\rho }^{+}\gamma )=({8.7}_{-2.7-1.1}^{+2.9+0.9})\times {10}^{-7}$, $\mathcal{B}(B^0\to {\rho }^0\gamma )=({7.8}_{-1.6-1.0}^{+1.7+0.9})\times {10}^{-7}$, and $\mathcal{B}(B^0\to \omega \gamma )=({4.0}_{-1.7}^{+1.9}\pm 1.3)\times {10}^{-7}$. We also report the isospin asymmetry $\Delta (\rho \gamma )=-{0.48}_{-0.19-0.09}^{+0.21+0.08}$ and the first measurement of the direct $CP$-violating asymmetry $A_{CP}(B^{+}\to {\rho }^{+}\gamma )=-0.11\pm 0.32\pm 0.09$, where the first and second errors are statistical and systematic, respectively.

• Received 30 April 2008
• Publisher error corrected 15 September 2008

DOI:https://doi.org/10.1103/PhysRevLett.101.111801