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

TL;DR

This paper reports measurements of branching fractions and direct CP asymmetries in specific B meson decays using Belle II data, providing results consistent with previous studies and demonstrating detector performance.

Contribution

First measurements of these decay modes' branching fractions and CP asymmetries using Belle II data, confirming detector capabilities and consistency with prior results.

Findings

Branching fraction for $B^+ o K^+ o ext{pi}^0$ measured as (11.9 ± 1.1(stat) ± 1.6(syst))×10^{-6}

Branching fraction for $B^+ o ext{pi}^+ ext{pi}^0$ measured as (5.5 ± 1.0(stat) ± 0.7(syst))×10^{-6}

CP asymmetry for $B^+ o K^+ ext{pi}^0$ is -0.09 ± 0.09(stat) ± 0.03(syst)

Abstract

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