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 -> mu(+)mu(-) 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 R-K, R-K*, and B-s -> mu mu alone results in a discrepancy with the Standard Model at 4.0 sigma, up from 3.5s in 2017. One-parameter scenarios with purely left-handed or with purely axial coupling to muons fit the data well and result in a -> 5 sigma 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 B-s -> mu(+) mu(-), 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(B-s -> mu(+) mu(-)) = (2.8 +/- 0.3) x 10(-9).

Automated summary

Motivated by new evidence for new physics in b -> sll transitions, including clean lepton-universality ratios and purely leptonic Bs -> mu(+)mu(-) decay measurements, a discrepancy with the Standard Model at 4.0 sigma has been quantified. Different scenarios, such as purely left-handed or purely axial coupling to muons, show a 5 sigma pull from the Standard Model. The analysis of new-physics contributions with both vector and axial-vector couplings to muons has a more restricted allowed region, primarily due to the more precise measurement of Bs -> mu(+) mu(-) and inclusion of angular observables data.