$\mathcal{B}(B\to \tau \nu )$ measurement with the hadronic FEI at Belle~II

We presented at Moriond EW 2025 a measurement of the branching fraction of $B\to \tau \nu$ decays using $(387\pm 6)\times {10}^6$ $\mathrm{{\rm Y}}(4S)$ collected between 2019 and 2022 with the Belle~II detector at the SuperKEKB $e^{+}{e}^{-}$ collider. We reconstruct the accompanying $B^{-}$ meson using the hadronic tagging method, while $B\to \tau \nu$ candidates are identified in the recoil. We find evidence for $B\to \tau \nu$ decays at 3.0 standard deviations, including systematic uncertainties. The measured branching fraction is $\mathcal{B}(B\to \tau \nu )=[1.24\pm 0.41\text{ (stat.)}\pm 0.19\text{ (syst.)}]\times {10}^{-4}$