Review of semileptonic B anomalies

Abstract

We review the current status and implications of the anomalies (i.e. deviations from the Standard Model predictions) in semi-leptonic B meson decays, both in the charged and in the neutral current. In b → sl+l− transitions significant tensions between measurements and the Standard Model predictions exist. They are most pronounced in the branching ratios BB→Kμ+μ− and BBs→φμ+μ− (albeit quite dependent on the form factors used) as well as in angular observables in B → K∗μ+μ− (the P ′ 5 anomaly). Because the measurements of BBs→μ+μ− and of the ratios R(K ) and R(K∗) agree reasonably well with the SM predictions, this points towards (dominantly) lepton flavour universal NP coupling vectorially to leptons,i.e. contributions to CU9 . In fact, global fits prefer this scenario over the SM hypothesis by 5.8σ. Concerning b → cτ ν transitions, R(D) and R(D∗) suggest constructive new physics at the level of 10% (w.r.t. the Standard Model amplitude) with a significance above 3σ. We discuss new physics explanations of both anomalies separately as well as possible combined explanations. In particular, a left-handed vector current solution to R(D(∗)), either via the U1 leptoquark or the combination of the scalar leptoquarks S1 and S3, leads to an effect in CU9 via an off-shell penguin with the right sign and magnitude and a combined significance (including a tree-level effect resulting in Cμ9 = −Cμ10 and R(D(∗))) of 6.3σ. Such a scenario can be tested with b → sτ +τ − decays. Finally, we point out an interesting possible correlation of R(D(∗)) with non-leptonic B anomalies