BELLE2-CONF-PH-2020-009

Measurement of the semileptonic $\bar{B^0} \rightarrow D^{*} \ell \nu_{\ell}$ branching fraction with fully reconstructed $B$ meson decays and 34.6 fb$^{-1}$ of Belle~II data

Abstract: We present a first measurement of the $\bar{B^0} \rightarrow D^{*} \ell \nu_{\ell}$ branching fraction using fully reconstructed $B$ meson decays employing the Full Event Interpretation algorithm. Collision events corresponding to an integrated luminosity of \lumi are analyzed, which were recorded by the Belle~II detector operated at the SuperKEKB accelerator complex. We measure 4.51 \pm 0.41_{stat} \pm 0.27_{syst} \pm0.45_{\pi_s}, with the first and second error denoting the statistical and systematic uncertainty, respectively, and the third dominant uncertainty is from the slow pion reconstruction efficiency.

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