Measurement of the branching fraction ratio RK at large dilepton invariant mass
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13130_2025_Article_26774.pdf
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Author(s)
Aaij, R.
Abdelmotteleb, A. S. W.
Abellan Beteta, C.
Abudinén, F.
Ackernley, T.
Adefisoye, A. A.
Adeva, B.
Adinolfi, M.
Adlarson, P.
Agapopoulou, C.
Date Issued
July 17, 2025
Journal
Journal of High Energy Physics
Publisher
Springer Berlin Heidelberg
Citation
The LHCb collaboration., Aaij, R., Abdelmotteleb, A.S.W. et al. Measurement of the branching fraction ratio RK at large dilepton invariant mass. J. High Energ. Phys. 2025, 198 (2025).
Version
Final published version
Abstract
A test of lepton universality between muons and electrons is performed using B+ → K+ℓ+ℓ− decays (where ℓ = e, μ), in the dilepton invariant-mass-squared region above 14.3 GeV2/c4. The data used for the measurement consists of beauty meson decays produced in proton-proton collisions, corresponding to an integrated luminosity of 9 fb−1, collected by the LHCb experiment between 2011 and 2018. The ratio of branching fractions for B+ → K+μ+μ− and B+ → K+e+e− decays is measured to be R K = 1.0 8 − 0.09 + 0.11 stat − 0.04 + 0.04 syst , which is consistent with the Standard Model prediction of unity. This constitutes the most precise test of lepton flavour universality using B+ → K+ℓ+ℓ− decays with dilepton invariant-mass-squared above the ψ(2S) mass, whilst being the first of its kind at a hadron collider.
MIT Department
Massachusetts Institute of Technology. Laboratory for Nuclear Science
MIT Kavli Institute for Astrophysics and Space Research
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DOI of Published Version
https://doi.org/10.1007/JHEP07(2025)198
