$B \to K^*(\to K\pi) \ell^+\ell^-$ theory and the global picture: What's next?

TL;DR

This paper reviews the current status of LHC anomalies in $b o s\,\ell^+\ell^-$ decays, emphasizing the $B \to K^* \to K\pi \ell^+\ell^-$ mode, and suggests focusing on optimized observables to probe lepton-flavour universality violations.

Contribution

It critically reassesses hadronic uncertainties and proposes studying $Q_i$ observables to improve sensitivity to new physics and reduce theoretical uncertainties.

Findings

Global fits show deviations above 4σ indicating potential new physics.

Hadronic uncertainties are significant but can be mitigated with optimized observables.

Lepton-flavour universality violations are a promising avenue for future research.

Abstract

The present status of the LHC anomalies found in exclusive semileptonic $b\to s\ell^+\ell^-$ decays is discussed with special emphasis on the exclusive 4-body angular distribution $B \to K^*(\to K\pi)\ell^+\ell^-$. 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$\sigma$ for different New Physics scenarios. Finally, we propose as the next step in the field to focus on the study of optimized observables that compare electron and muon modes, sensitive to lepton-flavour universality violations and free from hadronic uncertainties (including charm) in the SM, the so called $Q_i$ observables.