BELLE2-NOTE-PH-2022-032 BELLE2-PUB-DRAFT-2023-015 BELLE2-PUB-PH-2024-001

A test of lepton flavor universality with a measurement of $R(D^{*})$ using hadronic $B$ tagging at the Belle~II experiment

The Belle II Collaboration

05 January 2024

Abstract: The ratio of branching fractions $R(D^{*}) = \mathcal{B}(\overline{B} \rightarrow D^{*} \tau^{-} \overline{\nu}_{\tau})$/$\mathcal{B} (\overline{B} \rightarrow D^{*} \ell^{-} \overline{\nu}_{\ell})$, where $\ell$ is an electron or muon, is measured using a Belle~II data sample with an integrated luminosity of $189~\mathrm{fb}^{-1}$ at the SuperKEKB asymmetric-energy $e^{+} e^{-}$ collider. Data is collected at the $\Upsilon(\mathrm{4S})$ resonance, and one $B$ meson in the $\Upsilon(\mathrm{4S})\rightarrow B\overline{B}$ decay is fully reconstructed in hadronic decay modes. The accompanying signal $B$ meson is reconstructed as $\overline{B}\rightarrow D^{*} \tau^{-}\overline{\nu}_{\tau}$ using leptonic $\tau$ decays. The normalization decay, $\overline{B}\rightarrow D^{*} \ell^{-} \overline{\nu}_{\ell}$ produces the same observable final state particles. The ratio of branching fractions is extracted in a simultaneous fit to two signal-discriminating variables in both channels and yields $R(D^{*}) = 0.262~_{-0.039}^{+0.041}(\mathrm{stat})~_{-0.032}^{+0.035}(\mathrm{syst})$. This result is consistent with the current world average and with standard model predictions.

Keyword(s): R(D*) ; D*taunu ; FEI ; Hadronic tag ; Leptonic tau decay ; Semileptonic ; Semitauonic

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Belle II Notes (Internal) > Belle II Notes : Physics
Papers > Paper Drafts (Internal)
Papers > Papers : Physics

 Record created 2024-01-05, last modified 2024-01-11

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