Lifting Effective-Field-Theory Degeneracies in Semileptonic Heavy-Baryon Decays

Abstract

Semileptonic heavy-baryon decays provide a sensitive probe of the helicity structure underlying possible lepton-flavor universality violation in $b\to c\,τ\barν_τ$ transitions. We perform an effective-field-theory analysis of $Λ_b\toΛ_cτ\barν_τ$ and related baryonic modes using lattice-QCD helicity form factors with full covariance propagation. Propagating meson-compatible EFT solutions into the baryonic observable space$(R_{Λ_c},\,P_τ,\,A_{\rm FB})$, we show that tau polarization provides the leading source of sensitivity for lifting EFT degeneracies that remain unresolved in current measurements of $R(D)$ and $R(D^\ast)$. Vector-like and tensor-like solutions remain clustered near theStandard-Model prediction, whereas scalar-containing directions produce large polarization displacements and characteristic low-$q^2$ deformations of the normalized differential spectrum. A covariance-aware analysis demonstrates that baryonic polarization and differential observables provide complementary and independent information on the Lorentz structure of semileptonic new physics. $P_τ(Λ_b\toΛ_cτ\barν_τ)$ and the low-$q^2$ spectrum as particularly powerful probes for future tests of semitauonic flavor anomalies at LHCb and future flavor facilities.