Semi-inclusive Lepton Flavor Universality ratio in $b\to s\ell^+\ell^-$ transitions

TL;DR

This paper proposes a semi-inclusive ratio, $R_\Sigma$, to test muon-electron universality in $b\to s\ell^+\ell^-$ decays at $e^+e^-$ B-factories, aiming to detect potential new physics with minimal theoretical uncertainty.

Contribution

The paper introduces a new semi-inclusive LFU ratio, $R_\Sigma$, enhancing sensitivity to short-distance LFU violations while maintaining theoretical clarity.

Findings

$R_\Sigma^{\rm SM}=1$ predicted by the Standard Model

Combining decay channels increases sensitivity to LFU violations

Provides a clean observable for testing new physics in $b\to s\ell^+\ell^-$ transitions

Abstract

We construct a semi-inclusive Lepton Flavour Universality (LFU) ratio, $R_\Sigma$, to test $\mu/e$ universality in $b\to s\ell^+\ell^-$ transitions at $e^+e^-$ $B$-meson factories. Combining different decay channels, this observable maximises the sensitivity to possible LFU violations of short distance origin, yet preserving a clean theoretical interpretation in case of a deviation from its Standard Model prediction, $R_\Sigma^{\rm SM}=1$.