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

TL;DR

This paper reports precise measurements of branching fractions and CP asymmetries in B meson decays at Belle II, testing the Standard Model and constraining new physics effects with a large data sample.

Contribution

First Belle II measurements of specific B decay branching fractions and CP asymmetries, providing important tests of the Standard Model and constraints on quark weak interactions.

Findings

Sum rule measurement consistent with zero within uncertainties

Results agree with Standard Model predictions

Provides constraints on non-standard physics effects

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.