Angular analysis of Λb → Λc( → Λ π) ℓ$$ \overline{\nu} $$

We revisit the decay $$ {\varLambda}_b^0\to {\varLambda}_c^{+}{\ell}^{-}\overline{v} $$ (l = e, μ, τ) with a subsequent two-body decay $$ {\varLambda}_c^{+}\to {\varLambda}^0{\pi}^{+} $$ in the Standard Model and in generic New Physics models. The decay’s joint four-differential angular distribution can be expressed in terms of ten angular observables, assuming negligible polarization of the initial Λb state. We present compact analytical results for all angular observables, which enables us to discuss their possible New Physics reach. We find that the decay at hand probes more and complementary independent combinations of Wilson coefficients compared to its mesonic counter parts $$ \overline{B}\to {D}^{\left(\ast \right)}{\ell}^{-}\overline{v} $$. Our result for the angular distribution disagrees with some of the results on scalar-vector interference terms in the literature. We provide numerical estimates for all angular observables based on lattice QCD results for the Λb→ Λc form factors and account for a recent measurement of the parity-violating parameter in $$ {\varLambda}_c^{+}\to {\varLambda}^0{\pi}^{+} $$ decays by BESIII. A numerical implementation of our results is made publicly available as part of the EOS software.