Global analysis of b → sℓℓ anomalies

Abstract

We present a detailed discussion of the current theoretical and experimental situation of the anomaly in the angular distribution of B → K * (→ Kπ)µ + µ − , observed at LHCb in the 1 fb −1 dataset and recently confirmed by the 3 fb −1 dataset. The impact of this data and other recent measurements on b → s + − transitions ( = e, µ) is considered. We review the observables of interest, focusing on their theoretical uncertainties and their sensitivity to New Physics, based on an analysis employing the QCD factorisation approach including several sources of hadronic uncertainties (form factors, power corrections, charmloop effects). We perform fits to New Physics contributions including experimental and theoretical correlations. The solution that we proposed in 2013 to solve the B → K * µ + µ − anomaly, with a contribution C NP 9 −1, is confirmed and reinforced. A wider range of New-Physics scenarios with high significances (between 4 and 5 σ) emerges from the fit, some of them being particularly relevant for model building. More data is needed to discriminate among them conclusively. The inclusion of b → se + e − observables increases the significance of the favoured scenarios under the hypothesis of New Physics breaking lepton flavour universality. Several tests illustrate the robustness of our conclusions.

Flavour anomalies after the R K ∗ measurement

“…The coherence of this pattern of deviations has been pointed out already after the measurement of R K with a subset of observables in [10,11] and in a full global analysis in [12,13].…”

B s → Kℓν ℓ and B (s) → π(K)ℓ + ℓ − decays at large recoil and CKM matrix elements

“…As seen from table 5, the theory predictions for the B → K + − branching fraction reveal some tension with the experimentally measured values, making this observable an important ingredient of the global fits of rare B decays (see e.g., [43]). Adding the characteristics of B → π + − and B s → K + − decays to the set of fitted observables will further extend the possibilities to test the Standard Model in the quark-flavour sector.…”

On the importance of electroweak corrections for B anomalies

“…The above setup is the most natural one to accommodate simultaneously and in a correlated way charged-and neutral-current anomalies. Moreover, it is favoured by global fit analyses of b → s + − data [16][17][18][19][20][21][22] including the very recent experimental result for R µ/e K * [54][55][56][57][58][59][60][61][62]. At the electroweak scale m EW , additional operators will arise from Lagrangian (2.3), due to the well-known phenomenon of operator mixing.…”

“…refs. [16][17][18][19][20][21][22]. In the recent literature, many studies focused on the experimental signatures implied by the solution of these anomalies in specific scenarios, including kaon observables [23,24], kinematic distributions in B decays [25][26][27][28][29][30][31][32][33][34][35], the lifetime of the B − c meson [36], Υ and ψ leptonic decays [37], tau lepton searches [38,39] and dark matter [40,41].…”