The LFU Ratio $R_\pi$ in the Standard Model and Beyond

TL;DR

This paper explores the potential for precise tests of muon-electron universality in B meson decays to pions and lepton pairs, providing accurate predictions within and beyond the Standard Model to detect possible new physics.

Contribution

It introduces numerical formulas for analyzing decay width ratios that enable high-precision tests of lepton universality in B decays across different models.

Findings

High-accuracy predictions for decay width ratios in wide dilepton mass regions.

Methods to extract short-distance physics information from potential deviations.

Framework applicable both within and beyond the Standard Model.

Abstract

We discuss the possibility of performing precise tests of $\mu/e$ universality in $B \to\pi \ell^+\ell^-$ decays. We show that in wide regions of the dilepton invariant mass spectrum the ratio between muonic and electronic decay widths can be predicted with high accuracy, both within and beyond the Standard Model. We present numerical expressions which can be used to extract precise information on short-distance dynamics if a deviation from universality is observed in the data.