Measurement of the Λ_b polarization and angular parameters in Λ_b → J/ψΛ decays from pp collisions at √s = 7 and 8 TeV

An analysis of the bottom baryon decay Λ_b → J/ψ(→ μ^+μ^−)Λ(→ pπ^−) is performed to measure the Λ_b polarization and three angular parameters in data from pp collisions at √s = 7 and 8 TeV, collected by the CMS experiment at the Large Hadron Collider. The Λ_b polarization is measured to be 0.00±0.06(stat)±0.06(syst) and the parity-violating asymmetry parameter is determined to be 0.14±0.14(stat)±0.10(syst). The measurements are compared to various theoretical predictions, including those from perturbative quantum chromodynamics.