Phenomenology of ${\Lambda}_b\to {\Lambda}_c\tau {\overline{\nu}}_{\tau }$ using lattice QCD calculations

Abstract

In a recent paper we studied the effect of new-physics operators with different Lorentz structures on the semileptonic ${\Lambda}_b\to {\Lambda}_c\tau {\overline{\nu}}_{\tau }$ decay. This decay is of interest in light of the R(D ^(*)) puzzle in the semileptonic $\overline{B}\to {D}^{\left(\ast \right)}\tau {\overline{\nu}}_{\tau }$ 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 $R\left({\Lambda}_c\right)=\mathrm{\mathcal{B}}\left[{\Lambda}_b\to {\Lambda}_c\tau {\overline{\nu}}_{\tau}\right]/\mathrm{\mathcal{B}}\left[{\Lambda}_b\to {\Lambda}_c\ell {\overline{\nu}}_{\ell}\right]$ can strongly constrain the NP parameters of models discussed for the R(D ^(*)) puzzle. We use form factors from lattice QCD to calculate all ${\Lambda}_b\to {\Lambda}_c\tau {\overline{\nu}}_{\tau }$ observables. The Λ _b → Λ _c tensor form factors had not previously been determined in lattice QCD, and we present new lattice results for these form factors here.