Bernat Capdevila

Patterns of New Physics in b → sℓ+ℓ− transitions in the light of recent data

A bstractIn the Standard Model (SM), the rare transitions where a bottom quark decays into a strange quark and a pair of light leptons exhibit a potential sensitivity to physics beyond the SM. In addition, the SM embeds Lepton Flavour Universality (LFU), leading to almost identical probabilities for muon and electron modes. The LHCb collaboration discovered a set of deviations from the SM expectations in decays to muons and also in ratios assessing LFU. Other experiments (Belle, ATLAS, CMS) found consistent measurements, albeit with large error bars. We perform a global fit to all available b → sℓ+ℓ− data (ℓ = e, μ) in a model-independent way allowing for different patterns of New Physics. For the first time, the NP hypothesis is preferred over the SM by 5 σ in a general case when NP can enter SM-like operators and their chirally-flipped partners. LFU violation is favoured with respect to LFU at the 3-4 σ level. We discuss the impact of LFU-violating New Physics on the observable P5′ from B → K∗μ+μ− and we compare our estimate for long-distance charm contributions with an empirical model recently proposed by a group of LHCb experimentalists. Finally, we discuss NP models able to describe this consistent pattern of deviations.

Assessing lepton-flavour non-universality from B →K ∗ ℓℓ angular analyses

A bstractThe B → K∗μμ decay exhibits deviations with respect to Standard Model expectations and the measurement of the ratio RK hints at a violation of lepton-flavour universality in B → Kℓℓ transitions. Both effects can be understood in model-independent fits as a short-distance contribution to the Wilson coefficient C9μ, with some room for similar contributions in other Wilson coefficients for b → sμμ transitions. We discuss how a full angular analysis of B → K∗ee and its comparison with B → K∗μμ could improve our understanding of these anomalies and help confirming their interpretation in terms of short-distance New Physics. We discuss several observables of interest in this context and provide predictions for them within the Standard Model as well as within several New Physics benchmark scenarios. We pay special attention to the sensitivity of these observables to hadronic uncertainties from SM contributions with charm loops.

Hadronic uncertainties in B → K∗μ+μ−: a state-of-the-art analysis

A bstractIn the absence of direct evidence for New Physics at present LHC energies, the focus is set on the anomalies and discrepancies recently observed in rare b → sℓℓ transitions which can be interpreted as indirect hints. Global fits have shown that an economical New Physics solution can simultaneously alleviate the tensions in the various channels and can lead to a significant improvement in the description of the data. Alternative explanations within the Standard Model for part of the observed anomalies have been proposed in terms of (unexpectedly large) hadronic effects at low dilepton invariant mass and attributing tensions in protected observables to statistical fluctuations or experimental errors. We review the treatment of hadronic uncertainties in this kinematic regime for one of the most important channels, B → K∗μ+μ−, in a pedagogical way. We provide detailed arguments showing that factorisable power corrections cannot account for the observed anomalies and that an explanation through long-distance charm contributions is disfavoured. Some optimized observables at very low dilepton invariant mass are shown to be protected against contributions from the semileptonic coefficient C9 (including any associated long-distance charm effects), enhancing their sensitivity to New Physics contributions to other Wilson coefficients. Finally, we discuss how the recent measurement of Q5 by Belle (and in the future by LHCb and Belle-II) may provide a robust cross-check of our arguments.

New physics in semileptonic B decays (

Recently, the LHC has found several anomalies in exclusive semileptonic b → sl+l− decays. In this proceeding, we summarise the most important results of our global analysis of the relevant decay modes. After a discussion of the hadronic uncertainties entering the theoretical predictions, we present an interpretation of the data in terms of generic new physics scenarios. To this end, we have performed model-independent fits of the corresponding Wilson coefficients to the data and have found that in certain scenarios the best fit point is prefererred over the Standard Model by a global significance of more than 4σ . Based on the results, the discrimination between high-scale new physics and low-energy QCD effects as well as the possibility of lepton-flavour universality violation are discussed.

Predictions for

The present status of the LHC anomalies found in exclusive semileptonic

B\to K^* l^+l^-

b\to s\ell^+\ell^-

: problems and prospects

decays is discussed with special emphasis on the exclusive 4-body angular distribution

Searching for New Physics with b→sτ+τ− Processes

B \to K^*(\to K\pi)\ell^+\ell^-

Are we overlooking Lepton Flavour Universal New Physics in

. The treatment of hadronic uncertainties in this mode is briefly reviewed, and some of the analyses in the literature are critically reassessed. The global picture provided by the global fit points to a coherent pattern of deviations with a significance substantially above 4

b\to s\ell\ell

\sigma