Implications of new evidence for lepton-universality violation in b →sl+l- decays

Motivated by renewed evidence for new physics in b→sℓℓ transitions in the form of LHCb's new measurements of theoretically clean lepton-universality ratios and the purely leptonic Bs→μ+μ- decay, we quantify the combined level of discrepancy with the Standard Model and fit values of short-distance Wilson coefficients. A combination of the clean observables RK, RK∗, and Bs→μμ alone results in a discrepancy with the Standard Model at 4.0σ, up from 3.5σ in 2017. One-parameter scenarios with purely left-handed or with purely axial coupling to muons fit the data well and result in a ∼5σ pull from the Standard Model. In a two-parameter fit of new-physics contributions with both vector and axial-vector couplings to muons the allowed region is much more restricted than in 2017, principally due to the much more precise result on Bs→μ+μ-, which probes the axial coupling to muons. Including angular observables data restricts the allowed region further. A by-product of our analysis is an updated average of BR(Bs→μ+μ-)=(2.8±0.3)×10-9.