Exclusive $B^0\to {\pi }^{-}{\ell }^{+}{\nu }_{\ell }$ Decays with Hadronic Full Event Interpretation Tagging in 34.6 fb${}^{-1}$ of Belle II Data

Abstract

We present the results of the re-discovery of the decay $B^0\to {\pi }^{-}{\ell }^{+}{\nu }_{\ell }$ in 34.6 fb${}^{-1}$ 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${}_{\mathrm{sys}}$) $\times 10^{-4}$.