A test of lepton universality, performed by measuring the ratio of the branching fractions of the B0 → K0* μ+ μ− and B0 → K0* e+ e− decays, R_K0∗ , is presented. The K0* 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, q2, to be R_K0∗ = 0.66{−0.07}{+0.11} (stat) ± 0.03 (syst) for 0.045 < q^2 < 1.1 GeV^2/c^4, R_K0∗ = 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_K0∗ 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.

Test of Lepton Universality with B0 → K0* ℓ+ ℓ− Decays

Capriotti, L.;
2017

Abstract

A test of lepton universality, performed by measuring the ratio of the branching fractions of the B0 → K0* μ+ μ− and B0 → K0* e+ e− decays, R_K0∗ , is presented. The K0* 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, q2, to be R_K0∗ = 0.66{−0.07}{+0.11} (stat) ± 0.03 (syst) for 0.045 < q^2 < 1.1 GeV^2/c^4, R_K0∗ = 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_K0∗ 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.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11577/3582678
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