Eur. Phys. J. C (2026) 86: 463
https://doi.org/10.1140/epjc/s10052-026-15601-7

Regular Article - Theoretical Physics

The angular observables of ${\mathrm{\Lambda }}_b\to {\mathrm{\Lambda }}_c(\to {\mathrm{\Lambda }}^0{\pi }^{+}){\tau }^{-}(\to {\pi }^{-}{\nu }_{\tau }){\overline{\nu }}_{\tau }$ within the paradigm of FCCC anomalies

¹ Department of Physics, Quaid-i-Azam University, 45320, Islamabad, Pakistan
² National Center for Physics, 44000, Islamabad, Pakistan

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Received: 24 February 2026
Accepted: 16 March 2026
Published online: 4 May 2026

Abstract

We present a global analysis of the current B-meson flavor anomalies and extend it to the baryonic sector through the decay ${\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}(\to {\mathrm{\Lambda }}^0{\pi }^{+}){\tau }^{-}(\to {\pi }^{-}{\nu }_{\tau }){\overline{\nu }}_{\tau }$. The lepton flavor universality ratios $R_{\tau /(\mu ,e)}(D_{}^{(\ast )})$, measured by BaBar, Belle, and LHCb, exhibit a combined $3.8\sigma$ deviation from Standard Model (SM) predictions. Using the latest HFLAV averages and imposing $B_c$-lifetime constraints on the branching ratio, $\mathcal{B}(B_c\to \tau \nu )<60\%,30\%,10\%$, we perform a global fit to the anomaly data and propagate the preferred new physics (NP) solutions to the full cascade decay ${\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}(\to {\mathrm{\Lambda }}^0{\pi }^{+}){\tau }^{-}(\to {\pi }^{-}{\nu }_{\tau }){\overline{\nu }}_{\tau }$. The mixed vector-scalar scenario $(C_{V_L},C_{S_R})$ emerges as the most favored NP solution, yielding the largest pull from the SM while remaining insensitive to branching-ratio constraints. The single-operator $C_{V_L}$ case identified as the next most competitive scenario. We study the impact of NP vector, scalar and tensor operators on a complete set of angular observables on the five-fold ${\mathrm{\Lambda }}_b$ decay using Lattice-QCD form factors and find that the scenarios $(\Re [C_{S_L}=4C_T],\Im [C_{S_L}=4C_T])$ and $(C_{S_L},C_{S_R})$ generate the largest deviations from the SM predictions. In particular, the observables ${\mathcal{K}}_{1c}$, ${\mathcal{K}}_{2ss}$, ${\mathcal{K}}_{2cc}$, and ${\mathcal{K}}_{4s}$ show the highest sensitivity to NP effects. The correlation analysis reveals distinctive NP patterns: the $(\Re [C_{S_L}=4C_T],\Im [C_{S_L}=4C_T])$ scenario exhibits inverse correlations among ${\mathcal{K}}_{1c}$ and ${\mathcal{K}}_{2ss,2cc,4s}$ and direct correlations between ${\mathcal{K}}_{2ss}$ and ${\mathcal{K}}_{2cc,4s}$, pointing to destructive helicity interference and a possible CP-violating phase, while the $(C_{S_L},C_{S_R})$ scenario displays complementary behavior consistent with CP-conserving dynamics. These results establish baryonic semileptonic decays as a powerful and independent probe of the $R_{\tau /(\mu ,e)}(D_{}^{(\ast )})$ anomalies, with future measurements providing critical tests of the underlying NP structure.