Signature of Lepton flavor universality violation in $B_s \to D_s\tau\nu$ semileptonic decays

TL;DR

This paper investigates potential signs of lepton flavor universality violation in $B_s o D_s au u$ decays by analyzing deviations in related semileptonic $B$ decay measurements and exploring new physics scenarios.

Contribution

It provides predictions for various observables in $B_s o D_s au u$ decays considering both standard model and new physics effects, addressing recent anomalies.

Findings

Predicted deviations in branching ratios and asymmetries under new physics scenarios.

Identification of observables sensitive to lepton flavor universality violation.

Constraints on new physics couplings from current experimental data.

Abstract

Deviation from the standard model prediction is observed in many semileptonic $B$ decays mediated via $b \to c$ charged current interactions. In particular, current experimental measurements of the ratio of branching ratio $R_D$ and $R_{D^{\ast}}$ in $B \rightarrow D^{(*)}l \nu$ decays disagree with standard model expectations at the level of about $4.1\sigma$. Moreover, recent measurement of the ratio of branching ratio $R_{J/\Psi}$ by LHCb, where $R_{J/\Psi} = \mathcal B(B_c \to J/\Psi\,\tau\nu)/\mathcal B(B_c \to J/\Psi\,\mu\nu)$, is more than $2\sigma$ away from the standard model prediction. In this context, we consider an effective Lagrangian in the presence of vector and scalar new physics couplings to study the implications of $R_D$ and $R_{D^{\ast}}$ anomalies in $B_s \to D_s\,\tau\nu$ decays. We give prediction of several observables such as branching ratio, ratio of branching ratio, forward backward asymmetry parameter, $\tau$ polarization fraction, and the convexity parameter for the $B_s \to D_s\,\tau\nu$ decays within the standard model and within various new physics scenarios.