Measurement of the Ratio of Branching Fractions $\mathcal{B}({B}_{c}^{+}→J/ψ{τ}^{+}{ν}_{τ})/\mathcal{B}({B}_{c}^{+}→J/ψ{μ}^{+}{ν}_{μ})$

From the source

A measurement of the ratio of semileptonic branching fractions $\mathcal{R}(J/\ensuremath{\psi})$, defined as $\mathcal{R}(J/\ensuremath{\psi})\ensuremath{\equiv}\phantom{\rule{0ex}{0ex}}\mathcal{B}({B}_{c}^{+}\ensuremath{\rightarrow}J/\ensuremath{\psi}{\ensu…