Measurement of the branching fractions and $CP$ asymmetries of $B^+ \rightarrow \pi^+ \pi^0$ and $B^+ \rightarrow K^+ \pi^0$ decays in 2019-2021 Belle II data

TL;DR

This paper reports precise measurements of branching fractions and CP asymmetries for specific B meson decays using Belle II data, providing results consistent with previous measurements and improving accuracy.

Contribution

First measurement of these decay modes' branching fractions and CP asymmetries using Belle II data from 2019-2021, enhancing precision over prior results.

Findings

Branching fraction for B+ → π+ π0: (6.12 ± 0.53 ± 0.53)×10⁻⁶

Branching fraction for B+ → K+ π0: (14.30 ± 0.69 ± 0.79)×10⁻⁶

CP asymmetries are consistent with world averages

Abstract

We determine the branching fractions ${\mathcal{B}}$ and $CP$ asymmetries ${\mathcal{A}_{{\it CP}}}$ of the decays $B^+ \rightarrow \pi^+ \pi^0$ and $B^+ \rightarrow K^+ \pi^0$. The results are based on a data set containing 198 million bottom-antibottom meson pairs corresponding to an integrated luminosity of $190\;\text{fb}^{-1}$ recorded by the Belle II detector in energy-asymmetric electron-positron collisions at the $\Upsilon (4S)$ resonance. We measure ${\mathcal{B}(B^+ \rightarrow \pi^+ \pi^0) = (6.12 \pm 0.53 \pm 0.53)\times 10^{-6}}$, ${\mathcal{B}(B^+ \rightarrow K^+ \pi^0) = (14.30 \pm 0.69 \pm 0.79)\times 10^{-6}}$, ${\mathcal{A}_{{\it CP}}(B^+ \rightarrow \pi^+ \pi^0) = -0.085 \pm 0.085 \pm 0.019}$, and ${\mathcal{A}_{{\it CP}}(B^+ \rightarrow K^+ \pi^0) = 0.014 \pm 0.047 \pm 0.010}$, where the first uncertainties are statistical and the second are systematic. These results improve a previous Belle II measurement and agree with the world averages.