The Angular Observables of $\Lambda_b \to \Lambda_c(\to \Lambda^0 \pi^+) \, \tau^-(\to \pi^- \nu_\tau)\, \bar{\nu}_\tau$ within the Paradigm of FCCC Anomalies

TL;DR

This paper analyzes baryonic decay observables related to B-meson flavor anomalies, identifying new physics scenarios that could explain deviations from the Standard Model and proposing angular measurements as sensitive probes.

Contribution

It extends the analysis of flavor anomalies to baryonic decays, identifying promising new physics solutions and highlighting key angular observables for future experimental tests.

Findings

The $(C_{V_L},C_{S_R})$ scenario is the most favored new physics solution.

Certain angular observables like $ ext{K}_{1c}$ and $ ext{K}_{2ss}$ show high sensitivity to new physics.

Correlation patterns suggest potential CP-violating phases in specific new physics scenarios.

Abstract

We present a global analysis of the current $B$-meson flavor anomalies and extend it to the baryonic sector through the decay $\Lambda_b^0 \to \Lambda_c^+(\to \Lambda^0 \pi^+) \tau^-(\to \pi^- \nu_\tau)\bar{\nu}_\tau$. The lepton flavor universality ratios $R_{\tau/(\mu,e)}(D^{(*)})$, measured by BaBar, Belle, and LHCb, exhibit a combined $3.8\sigma$ deviation from Standard Model (SM) predictions. Using the latest HFLAV averages and $B_c$-lifetime constraints, $\mathcal{B}(B_c \to \tau \nu) < 60\%, 30\%, 10\%$, found new physics (NP) solutions to the cascade decay $\Lambda_b^0 \to \Lambda_c^+(\to \Lambda^0 \pi^+) \tau^-(\to \pi^- \nu_\tau)\bar{\nu}_\tau$. The scenario $(C_{V_L},C_{S_R})$ emerges as the most favored NP solution, largest pull from the SM and insensitive to branching-ratio constraints; followed by $C_{V_L}$ case. We study the impact of NP operators on a complete set of angular observables on the five-fold $\Lambda_b$ 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 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 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 $R_{\tau/(\mu,e)}(D^{(*)})$ anomalies, with future measurements providing critical tests of the underlying NP structure.