Abstract
A measurement of the ratio of the branching fractions of the B(+) → K(+)μ(+)μ(-) and B(+) → K(+)e(+)e(-) decays is presented using proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb(-1), recorded with the LHCb experiment at center-of-mass energies of 7 and 8 TeV. The value of the ratio of branching fractions for the dilepton invariant mass squared range 1 < q(2) < 6 GeV(2)/c(4) is measured to be 0.745(-0.074)(+0.090)(stat) ± 0.036(syst). This value is the most precise measurement of the ratio of branching fractions to date and is compatible with the standard model prediction within 2.6 standard deviations.
Highlights
The decay Bþ → Kþlþl−, where l represents either a muon or an electron, is a b → s flavor-changing neutral current process. Such processes are highly suppressed in the standard model (SM) as they proceed through amplitudes involving electroweak loop diagrams
This makes the branching fraction of Bþ → Kþlþl− decays highly sensitive to the presence of virtual particles that are predicted to exist in extensions of the SM [1]
The decay rate of Bþ → Kþμþμ− has been measured by LHCb to a precision of 5% [2] and, the current theoretical uncertainties in the branching fraction are Oð30%Þ [3], these largely cancel in asymmetries or ratios of Bþ → Kþlþl− observables [2,4]
Summary
The decay Bþ → Kþlþl−, where l represents either a muon or an electron, is a b → s flavor-changing neutral current process. The value of RK is determined using the ratio of the relative branching fractions of the decays Bþ → Kþlþl− and Bþ → J=ψð→ lþl−ÞKþ, with l 1⁄4 e and μ, respectively.
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