Abstract
A measurement of the ratio of branching fractions of the decays B^{+}→K^{+}μ^{+}μ^{-} and B^{+}→K^{+}e^{+}e^{-} is presented. The proton-proton collision data used correspond to an integrated luminosity of 5.0 fb^{-1} recorded with the LHCb experiment at center-of-mass energies of 7, 8, and 13TeV. For the dilepton mass-squared range 1.1<q^{2}<6.0 GeV^{2}/c^{4} the ratio of branching fractions is measured to be R_{K}=0.846_{-0.054}^{+0.060}_{-0.014}^{+0.016}, where the first uncertainty is statistical and the second systematic. This is the most precise measurement of R_{K} to date and is compatible with the standard model at the level of 2.5 standard deviations.
Highlights
A measurement of the ratio of branching fractions of the decays Bþ → Kþμþμ− and Bþ → Kþeþe− is presented
Decays involving b → slþl− transitions, where l represents a lepton, are mediated by flavor-changing neutral currents. Such decays are suppressed in the standard model (SM), as they proceed only through amplitudes that involve electroweak loop diagrams
These processes are sensitive to virtual contributions from new particles, which could have masses that are inaccessible to direct searches for resonances, even at Large Hadron Collider experiments
Summary
4.88–6.20 5.08–5.70 5.18–5.60 5.18–5.60 channels, including Bþ → J=ψ ð→ μþμ−ÞKþ and Bþ → J=ψð→ eþe−ÞKþ. Candidate events are first required to pass a hardware trigger that selects either a high transverse momentum (pT) muon, or an electron, hadron, or photon with high transverse energy deposited in the calorimeters. In this analysis, it is required that Bþ → Kþμþμ− and Bþ → J=ψð→ μþμ−ÞKþ candidates are triggered by one of the muons, whereas Bþ → Kþeþe− and Bþ → J=ψð→ eþe−ÞKþ candidates are required to be triggered in one of three ways: by either one of the electrons, by the kaon from the Bþ decay, or by particles in the event that are not part of the signal candidate.
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