Measurement of the CKM angle $\phi_3$ at Belle II

TL;DR

The paper discusses the Belle II experiment's efforts to precisely measure the CKM angle φ3, highlighting the importance of large datasets and the experiment's progress towards achieving a 1° measurement precision.

Contribution

This work presents the initial sensitivities and expected improvements in measuring φ3 using Belle II's large dataset and comprehensive decay channels.

Findings

First physics collisions recorded in April 2018

Expected to achieve 1° precision in φ3 measurement

Progress towards collecting 50 ab^{-1} of data

Abstract

The precise measurement of the CKM angle $\phi_3$ is important to further test the Standard Model description of $CP$ violation. The small values of the branching fractions of the decays involved in the measurement limits the precision, hence a larger dataset has to be accumulated to improve the precision. The Belle~II experiment at the SuperKEKB asymmetric-energy $e^+e^-$ collider aims to collect 50~ab$^{-1}$ of data, a factor of 50 more than that of its predecessor Belle. The accelerator has been successfully commissioned in 2016 and the first physics collisions were recorded in April 2018. The best sensitivity to $\phi_3$ can be achieved by harnessing all possible final states of $B \to D^{(*)}K^{(*)}$ decays. With the full dataset, Belle~II is expected to achieve a precision of 1$^{\circ}$ for the angle $\phi_3$. The expected sensitivities and rediscoveries from 2018 data are presented here.