Test of lepton flavor universality inB±â†’K±µ+µ-andB±â†’K±e+e-decays in proton-proton collisions ats=13TeV.

ABSTRACT

A test of lepton flavor universality inB±â†’K±µ+µ-andB±â†’K±e+e-decays, as well as a measurement of differential and integrated branching fractions of a nonresonantB±â†’K±µ+µ-decay are presented. The analysis is made possible by a dedicated data set of proton-proton collisions ats=13TeVrecorded in 2018, by the CMS experiment at the LHC, using a special high-rate data stream designed for collecting about 10 billion unbiased b hadron decays. The ratio of the branching fractionsB(B±â†’K±µ+µ-)toB(B±â†’K±e+e-)is determined from the measured double ratioR(K)of these decays to the respective branching fractions of theB±â†’J/ψK±withJ/ψ→µ+µ-ande+e-decays, which allow for significant cancellation of systematic uncertainties. The ratioR(K)is measured in the range1.1electron channel. The integrated branching fraction in the sameq2range,B(B±â†’K±µ+µ-)=(12.42±0.68)×10-8, is consistent with the present world-average value and has a comparable precision.