A Light shed on Lepton Flavor Universality in B decays

TL;DR

This paper reviews the theoretical and experimental status of lepton flavor universality tests in B decays, highlighting potential signs of new physics if current anomalies are confirmed with higher significance.

Contribution

It provides a comprehensive review of theoretical frameworks and experimental results related to lepton flavor universality violations in B decays, including new model-independent analyses.

Findings

Current anomalies suggest possible violation of lepton flavor universality.

Future data could confirm effects at 5 sigma significance.

Potential first evidence of physics beyond the Standard Model.

Abstract

At the back of succeeding measurements of anomalies in semileptonic decays at LHCb and several collider experiments hinting at the possible violation of lepton flavor universality, we undertake a concise review of theoretical foundations of the tree- and loop-level $b$-hadron decays, $b \to c l \nu_l$ and $b \to s l^+ l^-$ along with experimental environments. We revisit the world averages for $R_{D(D^*)}$, $R_{K(K^*)}$, $R_{J/\psi}$, and $R_{\eta_c}$, for the semileptonic transitions and provide results within the framework of the relativistic independent quark model in addition to the results from model-independent studies. If the ongoing evaluation of the data of LHC Run 2 confirms the measurements of Run 1, then the statistical significance of the effect in each decay channel is likely to reach 5~$\sigma$. A confirmation of these measurements would soon turn out to be the first remarkable observation of physics beyond the Standard Model providing a wider outlook on the understanding of New Physics.