Measurements of the branching fraction ratio B ϕ → μ + μ − / B ϕ → e + e − $$ \mathcal{B}\left(\phi \to {\mu}^{+}{\mu}^{-}\right)/\mathcal{B}\left(\phi \to {\textrm{e}}^{+}{\textrm{e}}^{-}\right) $$ with charm meson decays

Abstract Measurements of the branching fraction ratio B ϕ → μ + μ − / B ϕ → e + e − $$ \mathcal{B}\left(\phi \to {\mu}^{+}{\mu}^{-}\right)/\mathcal{B}\left(\phi \to {e}^{+}{e}^{-}\right) $$ with D s + → π + ϕ $$ {D}_s^{+}\to {\pi}^{+}\phi $$ and D + → π + ϕ decays, denoted R ϕπ s $$ {R}_{\phi \pi}^s $$ and R ϕπ d $$ {R}_{\phi \pi}^d $$ , are presented. The analysis is performed using a dataset corresponding to an integrated luminosity of 5.4 fb −1 of pp collision data collected with the LHCb experiment. The branching fractions are normalised with respect to the B + → K + J/ψ(→ e + e − ) and B + → K + J/ψ(→ μ + μ − ) decay modes. The combination of the results yields R ϕπ = 1.022 ± 0.012 stat ± 0.048 syst . $$ {R}_{\phi \pi}=1.022\pm 0.012\left(\textrm{stat}\right)\pm 0.048\left(\textrm{syst}\right). $$ The result is compatible with previous measurements of the ϕ → ℓ + ℓ − branching fractions and predictions based on the Standard Model.