B-decay discrepancies after Moriond 2019

Abstract

AbstractFollowing the updated measurement of the lepton flavour universality (LFU) ratio $$R_K$$RK in $$B\rightarrow K\ell \ell $$B→Kℓℓ decays by LHCb, as well as a number of further measurements, e.g. $$R_{K^*}$$RK∗ by Belle and $$B_s \rightarrow \mu \mu $$Bs→μμ by ATLAS, we analyse the global status of new physics in $$b\rightarrow s$$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 $$C_9 = -C_{10}$$C9=-C10, well suited to UV-complete interpretations, is now favoured with respect to a muonic contribution to $$C_9$$C9 only. An even better fit is obtained by allowing an additional LFU shift in $$C_9$$C9. 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 $$b \rightarrow c$$b→c transitions. This scenario is naturally realized in the simplified $$U_1$$U1 leptoquark model. We also analyse simplified models where a LFU effect in $$b\rightarrow s\ell \ell $$b→sℓℓ 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.