Measurement of the branching fraction ratio RK at large dilepton invariant mass

This is the authors' abstract. We don't add key points for this paper.

A bstract A test of lepton universality between muons and electrons is performed using B + → K + ℓ + ℓ − decays (where ℓ = e , μ ), in the dilepton invariant-mass-squared region above 14.3 GeV 2 /c 4 . The data used for the measurement consists of beauty meson decays produced in proton-proton collisions, corresponding to an integrated luminosity of 9 fb − 1 , collected by the LHCb experiment between 2011 and 2018. The ratio of branching fractions for B + → K + μ + μ − and B + → K + e + e − decays is measured to be RK=1.08-0.09+0.11(stat)-0.04+0.04(syst) R K = 1.0 8 − 0.09 + 0.11 stat − 0.04 + 0.04 syst , which is consistent with the Standard Model prediction of unity. This constitutes the most precise test of lepton flavour universality using B + → K + ℓ + ℓ − decays with dilepton invariant-mass-squared above the ψ (2 S ) mass, whilst being the first of its kind at a hadron collider.