We use our lattice QCD computation of the $B_c\to J/\psi$ form factors to determine the differential decay rate for the semitauonic decay channel and construct the ratio of branching fractions $R(J/\psi )=\mathcal{B}(B_c^{-}\to J/\psi {\tau }^{-}{\overline{\nu }}_{\tau })/\mathcal{B}(B_c^{-}\to J/\psi {\mu }^{-}{\overline{\nu }}_{\mu })$. 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 $B\to D^{*}\ell \nu$, to $B_c\to J/\psi \ell \nu$ and make predictions for their values under different new physics scenarios.

中文翻译：

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R（J /ψ）和Bc-→J /ψℓ-ν¯l轻子风味的普遍性违反了格子QCD的观测

我们使用我们的点阵QCD计算 ${乙}_C\to Ĵ/\psi$ 形状因子来确定半τ衰变通道的微分衰减率并构造分支分数的比率 $\mathrm{[R}（Ĵ/\psi ）=\mathcal{乙}（{乙}_C^{-}\to Ĵ/\psi {\tau }^{-}{\overline{\nu }}_{\tau }）/\mathcal{乙}（{乙}_C^{-}\to Ĵ/\psi {\mu }^{-}{\overline{\nu }}_{\mu }）$。我们发现$\mathrm{[R}（Ĵ/\psi ）=0.2582（38）$并给出错误预算。我们还扩展了相关的角度可观察性，最近有人建议将其用于研究轻子风味普遍性违规效应。$乙\to d^{*}\ell \nu$， 至 ${乙}_C\to Ĵ/\psi \ell \nu$ 并在不同的新物理场景下对其值进行预测。