Measurement of the Λ b polarization and angular parameters in Λ b → J = ψ Λ decays from pp collisions at ffiffi s p = 7 and 8 TeV

An analysis of the bottom baryon decay Λb → J=ψð→ μþμ−ÞΛð→ pπ−Þ is performed to measure the Λb polarization and three angular parameters in data from pp collisions at ffiffi s p 1⁄4 7 and 8 TeV, collected by the CMS experiment at the Large Hadron Collider. The Λb polarization is measured to be 0.00 0.06ðstatÞ 0.06ðsystÞ and the parity-violating asymmetry parameter is determined to be 0.14 0.14ðstatÞ 0.10ðsystÞ. The measurements are compared to various theoretical predictions, including those from perturbative quantum chromodynamics.