Benjamin Oberhof

26 June 2019
J-Symposium 2019

Abstract: 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. The design luminosity of the machine is 8×1035 cm−2s−1 and the Belle II experiment aims to record 50 ab−1 of data, a factor of 50 more than its predecessor. From February to July 2018, the machine has completed a commissioning run, achieved a peak luminosity of 5.5×1033 cm−2s−1, and Belle II has recorded a data sample of about 0.5 fb−1. Main operation of SuperKEKB has started in March 2019. In this presentation we report a measurement of the time-dependent CP violation parameter for B0(B¯0)→J/ψK0S using this early data set. One neutral B meson is reconstructed in the J/ψK0S CP-eigenstate decay channel and the flavor of the accompanying B meson is identified to be either B0 or B¯0 from its decay products. We present a new concept for the time-dependent CP violation fit together with initial results for the parameters of B0 mixing-induced phenomena and the lifetime of B0.

Note: 15 min