Measurement of $B\to K^{*}(892)\gamma$ Branching Fractions and $CP$ and Isospin Asymmetries

We present an analysis of the decays $B^0\to K^{*0}(892)\gamma$ and $B^{+}\to K^{*+}(892)\gamma$ using a sample of about $383\times {10}^6$ $B\overline{B}$ events collected with the BABAR detector at the PEP-II asymmetric energy $B$ factory. We measure the branching fractions $\mathcal{B}(B^0\to K^{*0}\gamma )=(4.47\pm 0.10\pm 0.16)\times {10}^{-5}$ and $\mathcal{B}(B^{+}\to K^{*+}\gamma )=(4.22\pm 0.14\pm 0.16)\times {10}^{-5}$. We constrain the direct $CP$ asymmetry to be $-0.033<\mathcal{A}(B\to K^{*}\gamma )<0.028$ and the isospin asymmetry to be $0.017<{\Delta }_{0-}<0.116$, where the limits are determined by the 90% confidence interval and include both the statistical and systematic uncertainties.

Figure 1

$m_{\mathrm{ES}}$ and $\Delta E$ projections of the fits. The points are data, the solid line is the fit result, the dotted line is the $B\overline{B}$ background, and the dash-dotted line is the continuum background. The dashed line gives the total ($B\overline{B}$ and continuum) contribution to the background.

Figure 2

Fit of a single relativistic $P$-wave Breit-Wigner line shape (solid line) to the $K\pi$ invariant mass distribution of the sPlot of data (points). For the $K^{*0}\to K_S{\pi }^0$ and $K^{*+}\to K^{+}{\pi }^0$, the Breit-Wigner is convolved with a Gaussian of width 10 MeV.