Weak Decays of the $Λ_{b}$ Baryon in Light-Front Dynamics

Abstract

We investigate the exclusive semileptonic and nonleptonic $Λ_{b} \to Λ_{c}(p)$ decays within the Standard Model by using the light-front quark model. To determine the behavior of the $Λ_{b} \to Λ_{c}(p)$ transition form factors, we employ the Bethe-Salpeter formalism in the timelike region, effectively accounting for both valence and nonvalence contributions. Using these form factors, including nonvalence contributions, we obtain branching fractions of $Λ_b \to Λ_c\,\ell\,\barν_{\ell}$, $Λ_b \to Λ_c\,τ\,\barν_τ$, $Λ_b \to p\,\ell\,\barν_{\ell}$ and $Λ_b \to p\,τ\,\barν_τ$~($\ell=e$ or $μ$) are found to be around $5.39\%$, $1.41\%$, $3.33\times 10^{-4}$ and $2.08\times 10^{-4}$, respectively, which are consistent with the experimental measurements. The ratios of $R^{\ellτ}(Λ_{c})=\frac{{\cal B}({Λ_b}\to {Λ_c}\,τ\,\barν_τ)} {{\cal B}({Λ_b}\to {Λ_c}\,\ell\,\barν_l)}$ and $R^{\ellτ}(p)=\frac{{\cal B}({Λ_b}\to p\,τ\,\barν_τ)} {{\cal B}({Λ_b}\to p\,\ell\,\barν_l)}$, are given by $0.261^{+0.097}_{-0.117}$ and $0.624^{+0.119}_{-0.129}$, respectively. The forward-backward asymmetries in the above semilepton decays are also examined. Our results indicate that, within the light-front framework, the nonvalence contributions to the asymmetries are negligible compared to the $β$-induced uncertainties. In addition, we calculate the branching ratios for the nonleptonic decays of $Λ_{b}\to Λ_{c}(p)\,M$ with $M$ being the pseudo scalar and vector mesons with the results found to be consistent with the current experimental data.