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− 0.07 (stat) ± 0.03 (syst) for 0.045 < q 2 < 1.1 GeV 2 /c 4 , 0.69 + 0.11 − 0.07 (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.

Overview of rare B-decays

“…While both measurements are compatible with the SM, a deviation of 2.6σ is observed only for the muon channel, in good compatibility with the LHCb and ATLAS results. The same discrepancy is not observed in the electron channel, which point to the same direction of the LFU test results [19,20]. Figure 6 compares the observed values for P 5 with the theoretical expectation in the muonic channel (left), and the measured P 5,µ and P 5,e from Belle (right).…”

Lepton polarization asymmetries in rare semi-tauonic $$ b \rightarrow s $$ b → s exclusive decays at FCC-ee

“…1,u , F (9) 2,u ) are found in [60], while F (7) 8 , F (9) 8 are found in [61]. Finally, the charm-loop function entering the expression of…”

“…Such an example is illustrated in Fig. 10 for imaginary δC 9 . We observe that no large effects in single tau polarization asymmetries are induced in this case (similar comments for P − N (V ) would also apply for an imaginary δC 10 , and, moreover, imaginary values for C 9 , C 10 ).…”

“…a e-mail: luiz.vale@th.u-psud.fr [9,10], thus suggesting violations of lepton flavor universality (LFU). Such effects can only arise from physics beyond the SM.…”

SUSY flavour / Flavour sector in BSM scenarios

“…Concerning b → s + − processes, R(K) [8] and R(K * ) [9] show a combined significance for LFU violation at the 4 σ level [10][11][12][13][14]. Taking into account all other b → sµ + µ − observables (like P5 [15]) as well, the global fit even shows compelling evidence for NP above the 5 σ level [16] for several scenarios like NP in C 9 only, C 9 = −C 10 or C 9 = −C 9 .…”