Test of lepton universality using B+ -> K+ l+ l- at LHCb

by Alexander Shires (Technische Universitaet Dortmund (DE)), Ulrich Andreas Haisch (University of Oxford (GB))

Thursday 4 Sept 2014, 11:00 → 12:00 Europe/Zurich

4/2-011 - TH common room (CERN)

The b→sll transition is a flavour-changing neutral current which is suppressed in the standard model and therefore sensitive to the presence of new virtual particles. Recent results on the angular distribution of B→K*µ⁺µ⁻ decays show local deviations from the Standard Model predictions of over 3σ. In the standard model, b→sll transitions couple to different leptonic final states equally, with the exception of small Higgs effects. Many of the models proposed to solve the effects seen in B→K*µ⁺µ⁻ decays could contain lepton universality breaking effects. LHCb collaboration measures the ratio of the rates of B⁺ → K⁺µ⁺µ⁻ and B⁺→K⁺e⁺e⁻ decays, called R_K, using proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb⁻¹, recorded with the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The value of the ratio of branching fractions for the dilepton invariant mass squared range 1 < q² < 6 GeV²/c⁴ is measured to be R_K = 0.745+0.090 −0.074 (stat) ± 0.036 (syst). This value of R_K is the most precise measurement of the ratio of branching fractions to date. This is compatible with the SM prediction within 2.6 standard deviations.

Paper arXiv:1406.6482.pdf

Slides cct.pdf RK.pdf