Measurements of branching fractions for $B^{+}\to {\rho }^{+}\gamma$, $B^0\to {\rho }^0\gamma$, and $B^0\to \omega \gamma$

We present branching fraction measurements for the radiative decays $B^{+}\to {\rho }^{+}\gamma$, $B^0\to {\rho }^0\gamma$, and $B^0\to \omega \gamma$. The analysis is based on a data sample of $465\times {10}^6$ $B\overline{B}$ events collected with the BABAR detector at the PEP-II asymmetric-energy $B$ Factory located at the Stanford Linear Accelerator Center. We find $\mathcal{B}(B^{+}\to {\rho }^{+}\gamma )=({1.20}_{-0.37}^{+0.42}\pm 0.20)\times {10}^{-6}$, $\mathcal{B}(B^0\to {\rho }^0\gamma )=({0.97}_{-0.22}^{+0.24}\pm 0.06)\times {10}^{-6}$, and a 90% C.L. upper limit $\mathcal{B}(B^0\to \omega \gamma )<0.9\times {10}^{-6}$, where the first error is statistical and the second is systematic. We also measure the isospin-violating quantity $\Gamma (B^{+}\to {\rho }^{+}\gamma )/2\Gamma (B^0\to {\rho }^0\gamma )-1=-{0.43}_{-0.22}^{+0.25}\pm 0.10$.

Figure 1

Performance of the charged-pion identification requirement applied to $B\to \rho \gamma$ decays, evaluated using the $D^{*}$ control sample. Filled circles are for ${\pi }^{\pm }$ efficiency and use the left-hand scale. Open circles are for $K^{\pm }$ misidentification and use the right-hand scale. The plot on the left shows results for continuum MC events and the plot on the right shows results for data.

Figure 2

Distributions of the BDT output for $B^0\to {\rho }^0\gamma$ in signal (dashed line) and background (dotted line) MC samples. The distributions are normalized to the same area.

Figure 3

$\Delta E$ and $m_{\mathrm{ES}}$ projections of the fits for the decay modes $B^{+}\to {\rho }^{+}\gamma$ (top panels), $B^0\to {\rho }^0\gamma$ (middle panels), and $B^0\to \omega \gamma$ (bottom panels). For illustrative purposes only, these plots are made by requiring $-0.2<\Delta E<0.1\mathrm{GeV}$ for the $m_{\mathrm{ES}}$ projections and $m_{\mathrm{ES}}>5.27\mathrm{GeV}/c^2$ for the $\Delta E$ projections. The points are data, the solid line is the fit result, the dashed line is the sum of $B$ backgrounds, and the dash-dotted and dotted lines are the contributions from continuum background and signal, respectively.