Measurement of the Lambda_b polarization and angular parameters in Lambda_b -> J/psi Lambda decays from pp collisions at sqrt(s) = 7 and 8 TeV

An analysis of the bottom baryon decay Λb→J/ψ(→μ+μ−)Λ(→pπ−) is performed to measure the Λb 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 Λb 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.