Assessing Lepton Flavor Universality Violations in Semileptonic Decays

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, $b\to cl{\nu }_l$ 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 ${\mathcal{R}}_{D(D^{\ast })}$ and ${\mathcal{R}}_{K(K^{\ast })}$ 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.

v2: revised and updated according to referee comments; comments, feedbacks and discussions are very much welcome!

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