Measurement of B → K*(892)γ decays at Belle II

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Abstract We present measurements of B → K *(892)γ decays using 365 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 ± 6) × 106 Υ(4S) events. We measure branching fractions ( $$\mathcal{B}$$ ) and CP asymmetries ( $${\mathcal{A}}_{CP}$$ ) for both B 0 → K *0 γ and B + → K *+ γ decays. The difference in CP asymmetries ( $$\Delta {\mathcal{A}}_{CP}$$ ) and the isospin asymmetry (∆0+) between these neutral and charged channels are also measured. We obtain the following branching fractions and CP asymmetries: $$\mathcal{B}\left({B}^{0}\to {K}^{*0}\gamma \right)=\left(4.14\pm 0.10\pm 0.11\right)\times {10}^{-5}$$ , $$\mathcal{B}\left({B}^{+}\to {K}^{*+}\gamma \right)=\left(4.04\pm {0.13}_{-0.15}^{+0.13}\right)\times {10}^{-5}$$ , $${\mathcal{A}}_{CP}\left({B}^{0}\to {K}^{*0}\gamma \right)=\left(-3.3\pm 2.3\pm 0.4\right)\%$$ , and $${\Delta}{\mathcal{A}}_{CP}\left({B}^{+}\to {K}^{*+}\gamma \right)=\left(-0.7\pm 2.9\pm 0.5\right)\%$$ . The measured difference in CP asymmetries is $${\Delta}{\mathcal{A}}_{CP}=\left(+{2}.{6}\pm {3}.{8}\pm 0.{6}\right)\%$$ , and the measured isospin asymmetry is ∆0+ = (+4.8 ± 2.0 ± 1.8)%. The first uncertainties listed are statistical and the second are systematic. These results are consistent with world-average values and theory predictions.

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