Evidence for Isospin Violation and Measurement of $CP$ Asymmetries in $B\to K^{\ast }(892)\gamma$

We report the first evidence for isospin violation in $B\to K^{\ast }\gamma$ and the first measurement of difference of $CP$ asymmetries between $B^+ \to K^{*+} \gamma$and$B^0 \to K^{*0} \gamma$. This analysis is based on the data sample containing $772\times {10}^{6}B\bar{B}$ pairs that was collected with the Belle detector at the KEKB energy-asymmetric $e^{+}{e}^{-}$ collider. We find evidence for the isospin violation with a significance of 3.1$\sigma$, $\Delta_{0+} = (+6.2 \pm 1.5 ({\rm stat.}) \pm 0.6 ({\rm syst.}) \pm 1.2 (f_{±}/f_{00}))$%, where the third uncertainty is due to the uncertainty on the fraction of $B^{+}{B}^{-}$ to $B^0{\bar{B}}^0$ production in $\mathrm{{\rm Y}}(4S)$ decays. The measured value is consistent with predictions of the SM. The result for the difference of $CP$ asymmetries is $\Delta A_{CP} = (+2.4 \pm 2.8({\rm stat.}) \pm 0.5({\rm syst.}))$\mathrm{\%},consistentwithzero\mathrm{.}Themeasuredbranchingfractionsand$CP$asymmetriesforchargedandneutral$B$ meson decays are the most precise to date. We also calculate the ratio of branching fractions of $B^0 \to K^{*0} \gamma$to$B_s^0 \to \phi \gamma$.