Vladimir Chekelian

24 August 2019
19th Lomonosov Conference on Elementary Particle Physics

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 $8\times 10^{35}$ cm$^{-2}$s$^{-1}$ and the Belle II experiment aims to record 50 ab$^{-1}$ of data, a factor of 50 more than its predecessor. In 2018 the machine has completed a commissioning run, achieved a peak luminosity of $5.5\times 10^{33}$ cm$^{-2}$s$^{-1}$. Main operation of SuperKEKB has started in March 2019. In this presentation we report on a first look at the time-dependent CP violation using this early data set. One neutral $B$ meson is reconstructed in the $J/\psi K^0_S$ $CP$-eigenstate decay channel and the flavor of the accompanying $B$ meson is identified to be either $B^0$ or $\bar B^0$ from its decay products. We present a new concept for the time-dependent $CP$ violation fit together with initial results for the parameters of $B^0$ mixing-induced phenomena and the lifetime of $B^0$.

Keyword(s): CP violation ; TD CPV ; mixing
Note: 20 min