Measurement of the ratios of branching fractions $\mathcal{R}(D^{\ast })$ and $\mathcal{R}(D^0)$

Abstract

The ratios of branching fractions $\mathcal{R}(D^{\ast })\equiv \mathcal{B}(\bar{B}\to D^{\ast }{\tau }^{-}{\bar{\nu }}_{\tau })/\mathcal{B}(\bar{B}\to D^{\ast }{\mu }^{-}{\bar{\nu }}_{\mu })$ and $\mathcal{R}(D^0)\equiv \mathcal{B}(B^{-}\to D^0{\tau }^{-}{\bar{\nu }}_{\tau })/\mathcal{B}(B^{-}\to D^0{\mu }^{-}{\bar{\nu }}_{\mu })$ are measured, assuming isospin symmetry, using a sample of proton-proton collision data corresponding to 3.0 fb${}^{-1}$ of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode ${\tau }^{-}\to {\mu }^{-}{\nu }_{\tau }{\bar{\nu }}_{\mu }$. The measured values are $\mathcal{R}(D^{\ast })=0.281\pm 0.018\pm 0.024$ and $\mathcal{R}(D^0)=0.441\pm 0.060\pm 0.066$, where the first uncertainty is statistical and the second is systematic. The correlation between these measurements is $\rho =-0.43$. Results are consistent with the current average of these quantities and are at a combined 1.9 standard deviations from the predictions based on lepton flavor universality in the Standard Model.

arXiv commentAll figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-039.html (LHCb public pages)

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