Phenomenology of $Λ_b \to Λ_c τ\barν_τ$ using lattice QCD calculations

Abstract

In a recent paper we studied the effect of new-physics operators with different Lorentz structures on the semileptonic $Λ_b \to Λ_c τ\barν_τ$ decay. This decay is of interest in light of the $R({D^{(*)}})$ puzzle in the semileptonic $\bar{B} \to D^{(*)} τ{\barν}_τ$ decays. In this work we add tensor operators to extend our previous results and consider both model-independent new physics (NP) and specific classes of models proposed to address the $R({D^{(*)}})$ puzzle. We show that a measurement of $R(Λ_c) = {\cal B}[Λ_b \to Λ_c τ\barν_τ] / {\cal B}[Λ_b \to Λ_c \ell \barν_{\ell}]$ can strongly constrain the NP parameters of models discussed for the $R({D^{(*)}})$ puzzle. We use form factors from lattice QCD to calculate all $Λ_b \to Λ_c τ\barν_τ$ observables. The $Λ_b \to Λ_c$ tensor form factors had not previously been determined in lattice QCD, and we present new lattice results for these form factors here.

44 pages, 105 figures