We report on new flavor tagging algorithms developed to determine the quark-flavor content of bottom ( "Image missing") mesons at Belle II. The algorithms provide essential inputs for measurements of quark-flavor mixing and charge-parity violation. We validate and evaluate the performance of the algorithms using hadronic "Image missing" decays with flavor-specific final states reconstructed in a data set corresponding to an integrated luminosity of 62.8 fb$$^{-1}$$ - 1 , collected at the "Equation missing" resonance with the Belle II detector at the SuperKEKB collider. We measure the total effective tagging efficiency to be $$\begin{aligned} \varepsilon _\mathrm{eff} = \big (30.0 \pm 1.2(\text {stat}) \pm 0.4(\text {syst})\big )\% \end{aligned}$$ ε eff = ( 30.0 ± 1.2 ( stat ) ± 0.4 ( syst ) ) % for a category-based algorithm and $$\begin{aligned} \varepsilon _\mathrm{eff} = \big (28.8 \pm 1.2(\text {stat}) \pm 0.4(\text {syst})\big )\% \end{aligned}$$ ε eff = ( 28.8 ± 1.2 ( stat ) ± 0.4 ( syst ) ) % for a deep-learning-based algorithm.

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We present the results of the re-discovery of the decay B 0 → π − + ν 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 2 miss , with a significance of 5.69σ, and determine a total branching fraction of (1.58 ± 0.43 stat ± 0.07 sys ) ×10 −4 .

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