Λ_b→ΛJ/ψ decay in perturbative QCD

We calculate, the amplitudes involved in the heavy baryon nonleptonic decay Λ_b→ΛJ/ψ using perturbative QCD factorization theorem, which is expressed as convolutions of hard b quark decay amplitudes with the Λ_b baryon, Λ baryon, and J/ψ meson distribution amplitudes. It is found that nonfactorizable contributions dominate over factorizable ones. Because of the soft cancellation in pairs of nonfactorizable diagrams, the Λ_b→ΛJ/ψ decay is characterized by a large scale, such that perturbative QCD is applicable. Employing the distribution amplitudes determined in our previous works and from QCD sum rules, we derive the branching ratio B(Λ_b→ΛJ/ψ)=(1.7-5.3)×1O^-4 in agreement with data. We predict an asymmetry parameter α = -0.17 to -0.14 associated with the anisotropic angular distribution of the Λ baryons produced in polarized Λ_b baryon decays.