Centre d'études et d'expertise sur les risques, l'environnement, la mobilité et l'aménagement

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Following the updated measurement of the lepton flavour universality (LFU) ratio R K in B → K decays by LHCb, as well as a number of further measurements, e.g. R K * by Belle and B s → µµ by ATLAS, we analyse the global status of new physics in b → s transitions in the weak effective theory at the b-quark scale, in the Standard Model effective theory above the electroweak scale, and in simplified models of new physics. We find that the data continues to strongly prefer a solution with new physics in semi-leptonic Wilson coefficients. A purely muonic contribution to the combination C 9 = −C 10 , well suited to UV-complete interpretations, is now favoured with respect to a muonic contribution to C 9 only. An even better fit is obtained by allowing an additional LFU shift in C 9 . Such a shift can be renormalization-group induced from four-fermion operators above the electroweak scale, in particular from semi-tauonic operators, able to account for the potential discrepancies in b → c transitions. This scenario is naturally realized in the simplified U 1 leptoquark model. We also analyse simplified models where a LFU effect in b → s is induced radiatively from four-quark operators and show that such a setup is on the brink of exclusion by LHC di-jet resonance searches.