2019 November 25
2019 December 17
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. In this paper, we report the first steps toward measurement of the time-dependent CP violation parameter for $B^0(\bar B^0)\to J/\psi K^0_S$ using an early Belle II data set. Furthermore, we briefly present a technique to improve $\alpha/\phi_2$ measurement and provide estimates of its uncertainty with the full Belle II data set.