Measurement of $B \to K{}^{*}(892)γ$ decays at Belle II

We present measurements of $B \to K{}^{*}(892)γ$ decays using $365\,{\rm fb}^{-1}$ of data collected from 2019 to 2022 by the Belle~II experiment at the SuperKEKB asymmetric-energy $e^+e^-$ collider. The data sample contains $(387 \pm 6) \times 10^6$ $Υ(4S)$ events. We measure branching fractions ($\mathcal{B}$) and $C\!P$ asymmetries ($\mathcal{A}_{C\!P}$) for both $B^{0}\to K{}^{*0}γ$ and $B^{+}\to K{}^{*+}γ$ decays. The difference in $C\!P$ asymmetries ($Δ\mathcal{A}_{C\!P}$) and the isospin asymmetry ($Δ_{0+}$) between these neutral and charged channels are also measured. We obtain the following branching fractions and $C\!P$ asymmetries: $\mathcal{B} (B^{0} \to K{}^{*0}γ) = (4.14 \pm 0.10 \pm 0.11 ) \times 10^{-5}$, $\mathcal{B} (B^{+} \to K{}^{*+}γ) = (4.04 \pm 0.13 {}^{+0.13}_{-0.15} )\times 10^{-5}$, $\mathcal{A}_{C\!P} (B^{0} \to K{}^{*0}γ) = (-3.3 \pm 2.3 \pm 0.4 )\%$, and $\mathcal{A}_{C\!P} (B^{+} \to K{}^{*+}γ) = (-0.7 \pm 2.9 \pm 0.5 )\%$. The measured difference in $C\!P$ asymmetries is $Δ\mathcal{A}_{C\!P} = (+2.6 \pm 3.8 \pm 0.6 )\%$, and the measured isospin asymmetry is $Δ_{0+} = (+4.8 \pm 2.0 \pm 1.8 )\%$. The first uncertainties listed are statistical and the second are systematic. These results are consistent with world-average values and theory predictions.