Wehle SWEI-SHU HOU et al.2022-04-252022-04-252021319007https://www.scopus.com/inward/record.uri?eid=2-s2.0-85105348029&doi=10.1103%2fPhysRevLett.126.161801&partnerID=40&md5=04e7fe575e2e88940e377f36039def79https://scholars.lib.ntu.edu.tw/handle/123456789/606797We present a measurement of RK?, the branching fraction ratio B(B→K?μ+μ-)/B(B→K?e+e-), for both charged and neutral B mesons. The ratio for the charged case RK?+ is the first measurement ever performed. In addition, we report absolute branching fractions for the individual modes in bins of the squared dilepton invariant mass q2. The analysis is based on a data sample of 711 fb-1, containing 772×106 BB¯ events, recorded at the ?(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. The obtained results are consistent with standard model expectations. ? 2021 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.Atomic physics; Physics; Absolute branching fractions; Asymmetric energy; Belle detectors; Branching fractions; E+e- collider; Invariant mass; Lepton-flavor; Standard model; High energy physics; article; expectation; flavor; leptonjournal article10.1103/PhysRevLett.126.161801339614762-s2.0-85105348029