Benedikt Wach

26 July 2021
EPS-HEP 2021

Abstract: The CKM angle 𝛾 (𝜙3) of the unitarity triangle is the only one that is accessible with tree-level decays in a theoretically clean way. The key method to measure 𝛾 is through the interference between 𝐵+→𝐷0𝐾+ and 𝐵+→𝐷¯0𝐾+ decays that occurs if the final state of the charm-meson decay is accessible to both the 𝐷0 and 𝐷¯0 mesons. The Belle II experiment at the SuperKEKB energy-asymmetric 𝑒+𝑒− collider is a substantial upgrade of the B factory facility at the Japanese KEK laboratory. Belle II experiment aims to record 50 ab−1 of data, a factor of 50 more than its predecessor. With the ultimate Belle II data sample of 50 ab−1, a determination of 𝛾 with a precision of 1 degree or better is foreseen. Main operation of SuperKEKB started in March 2019 and results from the full available Belle II data set, which corresponds to approximately 100~fb−1, will be presented. The ratios of decay rates of Γ(𝐵−→𝐷(∗)0𝐾−)/Γ(𝐵−→𝐷(∗)0𝜋−) and Γ(𝐵¯0→𝐷(∗)+𝐾−)/Γ(𝐵¯0→𝐷(∗)+𝜋−) are measured. In addition, more detailed studies of 𝐵−→𝐷(𝐾0S𝜋+𝜋−)𝐾−, 𝐵−→𝐷(𝐾0S𝜋0)𝐾− and 𝐵−→𝐷∗0(𝐷0𝜋0)𝐾− decays are described; these modes are key to the accurate determination of 𝛾 at Belle II.