Measurement of CKM angle $\boldsymbol{ \phi_{3}} $ at Belle II

The CKM angle $ \phi_{3} $ is the only angle of the unitarity triangle that is accessible with tree-level decays in a theoretically clean way. The Belle II experiment is a substantial upgrade of the Belle detector and will operate at the SuperKEKB energy-asymmetric $ e^{+}e^{-} $ collider. The accelerator has already successfully completed the first phase of commissioning, with the first $ e^{+}e^{-} $ collisions recorded in 2018. The design luminosity of SuperKEKB is 8$ \times 10^{35}$ cm$^{-2}$s$^{-1}$ and the Belle II experiment aims to record 50 ab$ ^{-1} $ of data, a factor of 50 more than the Belle experiment. The key method to measure $ \phi_{3} $ is through the interference between $ B^{+} \to D^{0}K^{+} $ and $ B^{+} \to \overline{D}^{0}K^{+} $ decays, which occurs if the final state of the charm-meson decay is accessible to both the $ D^{0} $ and $ \overline{D}^{0} $ mesons. To achieve the best sensitivity, a large variety of $ D $ and $ B $ decay modes are required, which is possible at the Belle II experiment as almost any final state can be reconstructed, including those with photons. With the ultimate Belle II data sample of 50 ab$ ^{-1} $, a determination of $ \phi_{3} $ with a precision of 1$^{\rm o} $ or better is foreseen.