Test of lepton flavor universality and search for lepton flavor violation in B → K?? decays
Journal
Journal of High Energy Physics
Journal Volume
2021
Journal Issue
3
Date Issued
2021
Author(s)
Abstract
We present measurements of the branching fractions for the decays B → Kμ+μ? and B → Ke+e?, and their ratio (RK), using a data sample of 711 fb?1 that contains 772 × 106BB¯ events. The data were collected at the ?(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e? collider. The ratio RK is measured in five bins of dilepton invariant-mass-squared (q2): q2 ? (0.1, 4.0), (4.00, 8.12), (1.0, 6.0), (10.2, 12.8) and (> 14.18) GeV2/c4, along with the whole q2 region. The RK value for q2 ? (1.0, 6.0) GeV2/c4 is 1.03?0.24+0.28 ± 0.01. The first and second uncertainties listed are statistical and systematic, respectively. All results for RK are consistent with Standard Model predictions. We also measure CP-averaged isospin asymmetries in the same q2 bins. The results are consistent with a null asymmetry, with the largest difference of 2.6 standard deviations occurring for the q2 ? (1.0, 6.0) GeV2/c4 bin in the mode with muon final states. The measured differential branching fractions, d? /dq2, are consistent with theoretical predictions for charged B decays, while the corresponding values are below the expectations for neutral B decays. We have also searched for lepton-flavor-violating B → Kμ±e? decays and set 90% confidence-level upper limits on the branching fraction in the range of 10?8 for B+ → K+μ±e?, and B0 → K0μ±e? modes. [Figure not available: see fulltext.] ? 2021, The Author(s).
Subjects
B physics; e+-e? Experiments; FCNC Interaction; Flavor physics; Flavour Changing Neutral Currents;
Type
journal article