Test of Lepton-Flavor Universality in B →k??+?- Decays at Belle

We 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.