Test of Lepton Flavor Universality in B± → K± Μ+μ- and B± → K± E+ E- Decays in Proton-Proton Collisions at √s=13 Tev

Abstract

A test of lepton flavor universality in B-+/- -> K +/- mu(+) mu(-) and B-+/- -> (K)+/- e(+) e(-) decays, as well as a measurement of differential and integrated branching fractions of a nonresonant B-+/- -> K-+/- mu(+)mu(-) decay are presented. The analysis is made possible by a dedicated data set of proton-proton collisions at root s = 13 TeV recorded 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 fractions B(B-+/- -> K-+/- mu(+) mu(-)) to B(B-+/- -> K-+/- e(+) e(-)) is determined from the measured double ratio R(K) of these decays to the respective branching fractions of the B-+/- -> J/psi K-+/- with J/psi -> mu(+)mu(-) and e(+) e(-) decays, which allow for significant cancellation of systematic uncertainties. The ratio R(K) is measured in the range 1.1 < q(2) < 6.0 GeV2, where q is the invariant mass of the lepton pair, and is found to be R(K) = 0.78(-0.23)(+0.47), in agreement with the standard model expectation R(K) approximate to 1. This measurement is limited by the statistical precision of the electron channel. The integrated branching fraction in the same q(2) range, B(B-+/- -> K-+/- mu(+) mu(-)) = (12.42 +/- 0.68) x 10(-8), is consistent with the present world-average value and has a comparable precision.