Towards establishing Lepton Flavour Universality violation in $\bar{B}\to \bar{K}^*\ell^+\ell^-$ decays

TL;DR

This paper proposes a novel amplitude analysis method for B meson decays to test lepton flavor universality violation, aiming to clarify potential new physics signals with minimal theoretical uncertainties.

Contribution

It introduces a simultaneous amplitude analysis of B decay modes to directly measure observables sensitive to lepton flavor universality violation, independent of nonperturbative QCD effects.

Findings

Method enables direct detection of non-equal lepton couplings.

Analysis is insensitive to nonperturbative QCD effects.

Potential for early discovery of new physics with LHCb data.

Abstract

Rare semileptonic $b \to s \ell^+ \ell^-$ transitions provide some of the most promising frameworks to search for new physics effects. Recent analyses of these decays have indicated an anomalous behaviour in measurements of angular distributions of the decay $B^0\to K^*\mu^+\mu^-$ and lepton-flavour-universality observables. Unambiguously establishing if these deviations have a common nature is of paramount importance in order to understand the observed pattern. We propose a novel approach to independently and complementary probe this hypothesis by performing a simultaneous amplitude analysis of $\bar{B}^0 \to \bar{K}^{*0} \mu^+\mu^-$ and $\bar{B}^0 \to \bar{K}^{*0} e^+e^-$ decays. This method enables the direct determination of observables that encode potential non-equal couplings of muons and electrons, and are found to be insensitive to nonperturbative QCD effects. If current hints of new physics are confirmed, our approach could allow an early discovery of physics beyond the standard model with LHCb run II data sets.