Test of lepton flavor universality violation in semileptonic $B_c^+$ meson decays at CMS

A measurement of the ratio of branching fractions $\mathrm{R}(\mathrm{J}/\psi) = \mathcal{B}(\mathrm{B}_{\mathrm{c}}^+\rightarrow\mathrm{J}/\psi\tau^+\nu_{\tau}) /$ $ \mathcal{B}(\mathrm{B}_{\mathrm{c}}^+\rightarrow\mathrm{J}/\psi\mu^+\nu_{\mu})$ in the $\mathrm{J}/\psi\rightarrow\mu^+\mu^-$, $\tau^+\rightarrow\mu^+\nu_{\mu}\nu_{\bar{\tau}}$ decay channel is presented. This measurement uses a sample of proton-proton collision data at a center of mass energy of 13 TeV collected by the CMS experiment in 2018 and corresponding to $59.7~\mathrm{fb}^{-1}$ of integrated luminosity. The measured ratio $\mathrm{R}(\mathrm{J}/\psi) = 0.17^{+ 0.18}_{- 0.17}~\mathrm{(stat.)}^{+ 0.21}_{- 0.22}~\mathrm{(syst.)}^{+ 0.19}_{- 0.18}~\mathrm{(theo.)} = 0.17 \pm 0.33$ agrees within 0.3 standard deviations with the value predicted by the standard model of particle physics.