Measurements of $\boldsymbol{B\rightarrow K\pi}$ and $\boldsymbol{B\rightarrow \pi\pi}$ Branching Fractions and $\boldsymbol{\mathcal{A}_{CP}}$ Asymmetries at Belle II

Abstract

Analyses of $B$ meson decays to charmless hadronic final states are an important part of the Belle II program. They are sensitive to effects from non-standard model physics and provide experimentally precise constraints on the weak interactions of quarks. We present recent Belle II results on branching fractions and direct $CP$-violating asymmetries of the decays $B^0 \rightarrow K^+\pi^-$, $B^+ \rightarrow K^+\pi^0$, $B^+ \rightarrow K^0\pi^+$, and $B^0 \rightarrow K^0\pi^0$, and use these to test the standard model through an isospin-based sum rule. In addition, we measure the branching fraction and direct $CP$ asymmetry of the decay $B^+ \rightarrow \pi^+\pi^0$ and the branching fraction of the decay $B^0 \rightarrow \pi^+\pi^-$, which contribute towards the determination of the CKM angle $\phi_2$. The data are collected with the Belle II detector from the SuperKEKB asymmetric-energy $e^+e^-$ collider, consisting of $387 \times 10^6$ $\Upsilon(4S)\rightarrow B\bar{B}$ events. We obtain $-0.03 \pm 0.13 \pm 0.04$ for the sum rule, in agreement with the standard model expectation of zero and with a precision comparable to the best existing determinations.