Test of lepton universality with B 0 → K *0 ℓ + ℓ - decays

Abstract

A test of lepton universality, performed by measuring the ratio of the branching fractions of the B 0 → K *0 μ + μ - and B 0 → K *0 e + e - decays, {R}_{K^{*0}} , is presented. The K *0 meson is reconstructed in the final state K + π -, which is required to have an invariant mass within 100 MeV /c 2 of the known K *(892)0 mass. The analysis is performed using proton-proton collision data, corresponding to an integrated luminosity of about 3 fb-1, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The ratio is measured in two regions of the dilepton invariant mass squared, q 2, to be {R}_{K^{*0}}= 0.66-+_{0.07}^{0.11}(stat)± 0.03(syst) for .045<{q}^2<1.1 GeV^2/{c}^4, 0.69-+_{0.07}^{0.11}(stat)± 0.05(syst) for 1.1<{q}^2<6.0 GeV^2/{c}^4. The corresponding 95.4% confidence level intervals are [0 .52 , 0 .89] and [0 .53 , 0 .94]. The results, which represent the most precise measurements of {R}_{K^{*0}} to date, are compatible with the Standard Model expectations at the level of 2.1-2.3 and 2.4-2.5 standard deviations in the two q 2 regions, respectively.