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

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.

9 pages, 3 figures

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• Fingerprinting CP-violating New Physics with $B\to K{\mu }^{+}{\mu }^{-}$
• Study of the $b\to d\ell \ell$ transitions in the Standard Model and test of New Physics sensitivities
• Maximising the physics potential of $B^{\pm }\to {\pi }^{\pm }{\mu }^{+}{\mu }^{-}$ decays
• Branching Fraction of the Decay $B^{+}\to {\pi }^{+}{\tau }^{+}{\tau }^{-}$ and Lepton Flavor Universality Test via the Ratio $R_{\pi }(\tau /\mu )$
• Theory Motivation: What measurements are needed?