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

Abstract

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

Comments: 44 pages, 105 figures