Nadia Toutounji ; Kevin Varvell ; Moritz Bauer ; Pablo Goldenzweig

05 August 2020

Abstract: We present the results of the re-discovery of the decay $B^0 \to \pi^- \ell^+ \nu_\ell$ in 34.6\invfb of Belle II data using hadronic $B$-tagging via the Full Event Interpretation algorithm. We observe 21 signal events on a background of 155 in a fit to the distribution of the square of the missing mass, $M_{\mathrm{miss}}^2$, with a significance of 5.69$\sigma$, and determine a total branching fraction of (1.58 $\pm$ 0.43$_{\mathrm{stat}}$ $\pm$ 0.07$_{\mathrm{sys}}$) $\times 10^{-4}$