$Λ_b \to Λ_c τ\barν_τ$ Decay in the Standard Model and with New Physics

Recently hints of lepton flavor non-universality emerged when the BaBar Collaboration observed deviations from the standard model predictions in $R(D^{(*)}) \equiv {\cal B}({\bar B} \to D^{(*)+} τ^- {\barν}_τ) / {\cal B}({\bar B} \to D^{(*)+} \ell^- {\barν}_\ell)$ ($\ell =e,μ$). Another test of this non-universality can be in the semi leptonic $Λ_{b}\toΛ_{c}τ\barν_τ$ decay. In this work we present predictions for this decay in the standard model and in the presence of new-physics operators with different Lorentz structures. We present the most general four-fold angular distribution for this decay including new physics. For phenomenology, we focus on predictions for the decay rate and the differential distribution in the momentum transfer squared $q^2$. In particular, we calculate $R_{Λ_{b}} = \frac{BR[Λ_b \to Λ_c τ\barν_τ]}{BR[Λ_b \to Λ_c \ell \barν_{\ell}]}$ where $\ell$ represents $μ$ or $e$, and find the standard model prediction to be around $0.3$ while the new physics operators can increase or slightly decrease this value.

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