Assessing lepton-flavour non-universality from $B\to K^*\ell\ell$ angular analyses

TL;DR

This paper investigates potential lepton-flavour non-universality in B meson decays through angular analyses, aiming to clarify anomalies and distinguish between Standard Model effects and new physics contributions.

Contribution

It proposes a comprehensive framework for analyzing angular observables in B→K*ee and B→K*μμ decays, highlighting their sensitivity to new physics and hadronic uncertainties.

Findings

Identifies key observables sensitive to lepton-flavour universality violation.

Provides Standard Model and new physics predictions for these observables.

Discusses the impact of charm-loop uncertainties on the interpretation of anomalies.

Abstract

The $B\to K^*\mu\mu$ decay exhibits deviations with respect to Standard Model expectations and the measurement of the ratio $R_K$ hints at a violation of lepton-flavour universality in $B\to K\ell\ell$ transitions. Both effects can be understood in model-independent fits as a short-distance contribution to the Wilson coefficient $C_{9\mu}$, with some room for similar contributions in other Wilson coefficients for $b\to s\mu\mu$ transitions. We discuss how a full angular analysis of $B\to K^*ee$ and its comparison with $B\to K^*\mu\mu$ 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.