Signature of Lepton Flavor Universality Violation in $$B_s \rightarrow D_s \tau \nu $$ Semileptonic Decays

Abstract

Deviation from the standard model prediction is observed in many semileptonic B decays mediated via \(b \rightarrow c\) charged current interactions. In particular, current experimental measurements of the ratio of branching ratio \(R_D\) and \(R_{D^{*}}\) 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 \(R_{J/\varPsi }\) by LHCb, where \(R_{J/\varPsi } = \mathcal B(B_c \rightarrow J/\varPsi \,\tau \nu )/\mathcal B(B_c \rightarrow J/\varPsi \,\mu \nu )\), 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 \(R_{D^{*}}\) anomalies in \(B_s \rightarrow D_s\,\tau \nu \) 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 \(B_s \rightarrow D_s\,\tau \nu \) decays within the standard model and within various new physics scenarios.