Polarized heavy baryon decays

We calculate the amplitudes involved in the heavy baryon nonleptonic decay Λ_b → ΛJ/ψ using perturbative QCD factorization theorem, which are 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. Employing the distribution amplitudes determined in our previous works, we derive the branching ratio B(Λ_b → ΛJ/ψ) = (1.65 ∼ 5.27) × 10^-4 in agreement with data. We predict an asymmetry parameter α = -0.17 ∼ -0.14 associated with the anisotropic angular distribution of the Λ baryons produced in polarized Λ_b baryon decays.