Assessing Lepton Flavor Universality Violations in Semileptonic Decays

TL;DR

This paper investigates potential violations of lepton flavor universality in semileptonic B-hadron decays, providing model-based predictions for observables and comparing them with existing data to explore signs of new physics beyond the Standard Model.

Contribution

It introduces a Relativistic Independent Quark Model approach to predict lepton flavor violating observables in B-hadron decays and compares these with lattice results, enhancing understanding of flavor dynamics.

Findings

Predictions for $ ext{R}_{J/ ext{psi}}$ and $ ext{R}_{ ext{eta}_c}$ across all $q^2$.

Comparison shows strong agreement between RIQM and lattice predictions.

Reassessment of global averages for $ ext{R}_D$, $ ext{R}_{D^*}$, $ ext{R}_K$, and $ ext{R}_{K^*}$.

Abstract

In light of recent measurements suggesting potential lepton flavor universality violations in semileptonic decays at collider experiments, this article provides a concise study of tree- and loop-level $B$-hadron semileptonic decays, $b \to c l \nu_l$ and $b \to s l^+ l^-$. We provide predictions for lepton flavor violating observables, $\mathcal{R}_{J/\psi}$ and $\mathcal{R}_{\eta_c}$, across the entire $q^2$ range. Our study employs the Relativistic Independent Quark Model (RIQM), highlighting a model-dependent approach to these observables. We compare our model's predictions with existing lattice predictions, demonstrating the strong applicability of the RIQM framework in describing $B_c$ decays. Additionally, we reassess global averages for $\mathcal{R}_{D(D^*)}$ and $\mathcal{R}_{K(K^*)}$ in semileptonic transitions. With the upcoming experimental upgrades and the anticipated Run 3 data on $B_c$ meson decays, rapid confirmation of these quantities could indicate significant evidence of physics beyond the Standard Model, thereby opening new pathways for understanding the complex flavor dynamics in $B$ meson decays.