Analysis of $b \to c \ell ν$ baryonic decay modes in SMEFT approach

TL;DR

This work investigates $b \to c \ell \nu$ transitions in heavy-baryon decays within the SMEFT framework, focusing on the exclusive processes $\Xi_b \to \Xi_c \tau^-\bar{\nu}_\tau$, $\Sigma_b \to \Sigma_c^{(*)} \tau^-\bar{\nu}_\tau$. By matching SMEFT operators to the low-energy LEFT and employing HQET-based hadronic form factors with Isgur-Wise functions, the authors quantify how NP couplings $C_{lq}^{(3)}$, $C_{lequ}^{(1)}$, and $C_{ledq}$ affect differential rates and angular observables across $q^2$. The analysis finds that 2D NP scenarios, particularly $(C_{lequ}^{(1)}, C_{ledq})$, can induce sizable deviations from SM predictions in branching fractions, forward-backward asymmetries, convexity, and lepton polarization, while 1D scenarios are largely inconsequential. These baryonic channels provide complementary probes to mesonic decays for constraining SMEFT NP and could become accessible with future experimental data. The study highlights the interconnected roles of SMEFT and LEFT in connecting high-scale NP to low-energy flavor observables across multiple decay modes.

Abstract

The flavor-changing neutral current decays of heavy bottom quark, alongside the flavor-changing charged current processes mediated by $b \to (c, u)$ in semileptonic $B$ decays are emerged as powerful tools for exploring physics beyond the Standard Model. In this work, we focus on the feasibility of interpreting the processes mediated by $b \to c τν$ transitions, in particular, the semileptonic $b$-baryonic decay modes $Σ_b \to Σ_c^{(*)} τ^-\barν_τ$ and $Ξ_b \to Ξ_c τ^-\barν_τ$ in the context of SMEFT approach. We perform a detailed analysis of the sensitivity of new physics operators on various observables such as branching ratio, forward-backward asymmetry parameter, lepton non-universal observable and the longitudinal polarization fraction of the $b$-baryonic decay channels.

Figures (13)

• Figure 1: Allowed parameter scan in 1$\sigma$ (green), 2$\sigma$ (magenta), and 3$\sigma$ (cyan) regions. The black star denotes the best-fit value.
• Figure 2: $d\text{B}r/dq^2$ and $A_{FB}$ for $\Xi_b \to \Xi_c \tau^- \bar{\nu}_\tau$ in $(C_{lq}^{(3)}, C_{lequ}^{(1)})$ (left), $(C_{lq}^{(3)}, C_{ledq})$ (middle), and $(C_{lequ}^{(1)}, C_{ledq})$ (right). Top panel: branching ratio, Bottom panel: forward-backward asymmetry.
• Figure 3: The $q^2$ distribution of convexity parameter of $\Xi_b \to \Xi_c \tau^-\bar{\nu}_\tau$ process. The description of couplings is same as Fig. \ref{['fig::BRCascade']}
• Figure 4: The $q^2$ dependence of the longitudinal polarization fraction $\Xi_b \to \Xi_c \tau^-\bar{\nu}_\tau$ process. The description of couplings is same as Fig. \ref{['fig::BRCascade']}.
• Figure 5: The $q^2$ behavior of $R_{\Sigma_b}$ in the $\Xi_b \to \Xi_c \tau^-\bar{\nu}_\tau$ process. The description of couplings is same as Fig. \ref{['fig::BRCascade']}.