A general effective field theory description of b → sl+l- lepton universality ratios

We construct an expression for a general lepton flavour universality (LFU) ratio, R-X, in b -> sl(+)l(-) decays in terms of a series of hadronic quantities which can be treated as nuisance parameters. This expression allows to include any LFU ratio in global fits of b -> sl(+)l(-)short-distance parameters, even in the absence of a precise knowledge of the corresponding hadronic structure. The absence of sizeable LFU violation and the approximate left-handed structure of the Standard Model amplitude imply that only a very limited set of hadronic parameters hamper the sensitivity of R-X to a possible LFU violation of short-distance origin. A global b -> sl(+)l(-) combination is performed including the measurement of R-pK for the first time, resulting in a significance of new physics of 4.2 sigma. In light of this, we evaluate the impact on the global significance of new physics using a set of experimentally promising non-exclusive R-X measurements that LHCb can perform, and find that they can significantly increase the discovery potential of the experiment. (C) 2022 The Authors. Published by Elsevier B.V.

Automated summary

We propose an expression for a general lepton flavour universality (LFU) ratio, R-X, in b -> sl(+)l(-) decays, and find that the sensitivity of R-X to a possible LFU violation is limited by a small set of hadronic parameters. By performing a global combination analysis, we obtain a new physics significance of 4.2 sigma and demonstrate that non-exclusive R-X measurements can significantly enhance the discovery potential of the experiment.