# Angular Analysis of \boldmath $\Lambda_b\to \Lambda_c (\to \Lambda \pi)\ell\bar\nu$

## TL;DR

This paper provides a detailed angular analysis of the decay mbda_b, deriving analytical expressions for angular observables to explore potential New Physics effects and comparing with existing literature.

## Contribution

It offers the first comprehensive analytical framework for angular observables in mbda_b decay, enabling enhanced sensitivity to New Physics beyond mesonic decay analyses.

## Key findings

- All angular observables derived analytically with compact formulas.
- Decay probes more independent Wilson coefficient combinations than mesonic decays.
- Numerical estimates based on lattice QCD and recent experimental data.

## Abstract

We revisit the decay $\Lambda_b^0\to \Lambda_c^+ \ell^-\bar\nu$ ($\ell = e,\mu,\tau$) with a subsequent two-body decay $\Lambda_c^+ \to \Lambda^0 \pi^+$ 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 $\Lambda_b$ 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 $\bar{B}\to D^{(*)}\ell^-\bar\nu$. Our result for the angular distribution is at variance 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 $\Lambda_b \to \Lambda_c$ form factors and account for a recent measurement of the parity-violating parameter in $\Lambda_c^+\to \Lambda^0\pi^+$ decays by BESIII. A numerical implementation of our results is made publicly available as part of the EOS software.