Measurements of the branching fraction ratio B(ϕ → µ +µ −)/B(ϕ → e +e −) with charm meson decays

Abstract

Measurements of the branching fraction ratio B(ϕ → µ +µ −)/B(ϕ → e +e −) with D+ s → π +ϕ and D+ → π +ϕ decays, denoted Rs ϕπ and Rd ϕπ, 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 Rϕπ = 1.022 ± 0.012 (stat) ± 0.048 (syst). The result is compatible with previous measurements of the ϕ → ℓ +ℓ − branching fractions and predictions based on the Standard Model.