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arXiv · 2007.06956

$R(J/\psi)$ and $B_c^- \rightarrow J/\psi \ell^-\bar{\nu}_\ell$ Lepton Flavor Universality Violating Observables from Lattice QCD

Judd Harrison·Christine T. H. Davies·Andrew Lytle
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Abstract

We use our lattice QCD computation of the $B_c\rightarrow J/\psi$ form factors to determine the differential decay rate for the semitauonic decay channel and construct the ratio of branching fractions $R(J/\psi) = \mathcal{B}(B_c^- \rightarrow J/\psi \tau^-\bar{\nu}_\tau)/\mathcal{B}(B_c^- \rightarrow J/\psi \mu^-\bar{\nu}_\mu)$. We find $R(J/\psi) = 0.2582(38)$ and give an error budget. We also extend the relevant angular observables, which were recently suggested for the study of lepton flavor universality violating effects in $B\rightarrow D^*\ell\nu$, to $B_c \rightarrow J/\psi\ell\nu$ and make predictions for their values under different new physics scenarios.

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Judd Harrison, Christine T. H. Davies, Andrew Lytle. 2020-07-14. $R(J/\psi)$ and $B_c^- \rightarrow J/\psi \ell^-\bar{\nu}_\ell$ Lepton Flavor Universality Violating Observables from Lattice QCD. https://doi.org/10.1103/physrevlett.125.222003

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