Search for Lepton-Universality Violation in B + → K + ℓ + ℓ − Decays

Abstract

A measurement of the ratio of branching fractions of the decays B + → K + μ + μ − and B + → K + e + e − is presented. The proton-proton collision data used correspond to an integrated luminosity of 5.0     fb − 1 recorded with the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV. For the dilepton mass-squared range 1.1 < q 2 < 6.0     GeV 2 / c 4 the ratio of branching fractions is measured to be R K = 0.84 6 + 0.060 − 0.054 + 0.016 − 0.014 , where the first uncertainty is statistical and the second systematic. This is the most precise measurement of R K to date and is compatible with the standard model at the level of 2.5 standard deviations