Measurements of branching fractions and direct $CP$-violating asymmetries in $B^+ \to K^+ π^0~\mbox{and}~π^+ π^0$ decays using 2019 and 2020 Belle II data

Abstract

We report measurements of branching fractions ($\mathcal{B}$) and direct $CP$-violating asymmetries (${\mathcal{A}}_{CP}$) for the decays $B^{+}\to K^{+}\ddot{I}{€}^0$ and $B^{+}\to \ddot{I}{€}^{+}\ddot{I}{€}^0$ reconstructed with the Belle II detector in a sample of asymmetric-energy electron-positron collisions at the $\hat{I}\yen (4S)$ resonance corresponding to 62.8 ${\text{fb}}^{-1}$ of integrated luminosity. The results are $\mathcal{B}(B^{+}\to K^{+}\ddot{I}{€}^0)=[11.9_{-1.0}^{+1.1}(\mathrm{stat})\pm 1.6(\mathrm{syst})]\times 10^{-6}$, $\mathcal{B}(B^{+}\to \ddot{I}{€}^{+}\ddot{I}{€}^0)=[5.5_{-0.9}^{+1.0}(\mathrm{stat})\pm 0.7(\mathrm{syst})]\times 10^{-6}$, ${\mathcal{A}}_{CP}(B^{+}\to K^{+}\ddot{I}{€}^0)=-0.09\pm 0.09(\mathrm{stat})\pm 0.03(\mathrm{syst})$, and ${\mathcal{A}}_{CP}(B^{+}\to \ddot{I}{€}^{+}\ddot{I}{€}^0)=-0.04\pm 0.17(\mathrm{stat})\pm 0.06(\mathrm{syst})$. The results are consistent with previous measurements and show a detector performance comparable with early Belle performance.

23 pages, 10 figures. Supporting material for Winter 2021 conferences