We present measurements of $B \to K{ }^{ *}(892)\gamma$ 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 $(387 \pm 6) \times 10^6$ $\Upsilon(4S)$ events. We measure branching fractions ($\mathcal{ B}$) and $C\!P$ asymmetries ($\mathcal{ A}_{ C\!P}$) for both $B^{ 0}\to K{ }^{ *0}\gamma$ and $B^{ +}\to K{ }^{ *+}\gamma$ decays. The difference in $C\!P$ asymmetries ($\Delta \mathcal{ A}_{ C\!P}$) and the isospin asymmetry ($\Delta_{ 0+}$) between these neutral and charged channels are also measured. We obtain the following branching fractions and $C\!P$ asymmetries: $\mathcal{ B} (B^{ 0} \to K{ }^{ *0}\gamma) = (4.14 \pm 0.10 \pm 0.11 ) \times 10^{ -5}$, $\mathcal{ B} (B^{ +} \to K{ }^{ *+}\gamma) = (4.04 \pm 0.13 { }^{ +0.13}_{ -0.15} )\times 10^{ -5}$, $\mathcal{ A}_{ C\!P} (B^{ 0} \to K{ }^{ *0}\gamma) = (-3.3 \pm 2.3 \pm 0.4 )\%$, and $\mathcal{ A}_{ C\!P} (B^{ +} \to K{ }^{ *+}\gamma) = (-0.7 \pm 2.9 \pm 0.5 )\%$. The measured difference in $C\!P$ asymmetries is $\Delta \mathcal{ A}_{ C\!P} = (+2.6 \pm 3.8 \pm 0.6 )\%$, and the measured isospin asymmetry is $\Delta_{ 0+} = (+4.8 \pm 2.0 \pm 1.8 )\%$. The first uncertainties listed are statistical and the second are systematic. These results are consistent with world-average values and theory predictions.
Categories: hep-ex