Semileptonic and leptonic B decay results from early Belle II data

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 $8\times 10^{35}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$ and the Belle II experiment aims to record $50{\mathrm{ab}}^{-1}$ of data, a factor of 50 more than its predecessor. From February to July 2018, SuperKEKB has completed a commissioning run, achieved a peak luminosity of $5.5\times 10^{33}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$, and Belle II recorded a data sample of about $0.5{\mathrm{fb}}^{-1}$. In this presentation we show first results from studying missing energy signatures, such as leptonic and semileptonic B meson decays based on this early Belle II data. We report first studies on re-measuring important standard candle processes, such as the abundant inclusive $B\to Xl\nu$ and $B\to D^{\ast }\ell \nu$ decays, and evaluate the performance of machine learning-based tagging algorithms. Furthermore, we also present an overview of the semileptonic B decays that will be measured in the upcoming years at Belle II and discuss prospects for important B-anomalies like R$(D)$ and R$(D^{\ast })$, as well as other tests of lepton flavor universality.

Proceedings of the 2019 Conference on Flavor Physics and CP Violation (FPCP2019)

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