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

Abstract

We present measurements of $B\to K{}^{\ast }(892)\gamma$ decays using $365{\mathrm{fb}}^{-1}$ of data collected from 2019 to 2022 by the Belle~II experiment at the SuperKEKB asymmetric-energy $e^{+}{e}^{-}$ collider. The data sample contains $(387\pm 6)\times 10^6$ ${\rm Y}(4S)$ events. We measure branching fractions ($\mathcal{B}$) and $CP$ asymmetries (${\mathcal{A}}_{CP}$) for both $B^0\to K{}^{\ast 0}\gamma$ and $B^{+}\to K{}^{\ast +}\gamma$ decays. The difference in $CP$ asymmetries ($\Delta {\mathcal{A}}_{CP}$) and the isospin asymmetry (${\Delta }_{0+}$) between these neutral and charged channels are also measured. We obtain the following branching fractions and $CP$ asymmetries: $\mathcal{B}(B^0\to K{}^{\ast 0}\gamma )=(4.14\pm 0.10\pm 0.11)\times 10^{-5}$, $\mathcal{B}(B^{+}\to K{}^{\ast +}\gamma )=(4.04\pm 0.13{}_{-0.15}^{+0.13})\times 10^{-5}$, ${\mathcal{A}}_{CP}(B^0\to K{}^{\ast 0}\gamma )=(-3.3\pm 2.3\pm 0.4)\%$, and ${\mathcal{A}}_{CP}(B^{+}\to K{}^{\ast +}\gamma )=(-0.7\pm 2.9\pm 0.5)\%$. The measured difference in $CP$ asymmetries is $\Delta {\mathcal{A}}_{CP}=(+2.6\pm 3.8\pm 0.6)\%$, 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.

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Cited by in corpus (1)

• Precise $K^{\ast }(892)\to K\pi$ branching fractions