Aad, G.ATLAS Collaboration,2016-11-162016-11-162014Physical Review D: Particles, Fields, Gravitation and Cosmology, 2014; 89(9):092009-1-092009-251550-23681550-2368http://hdl.handle.net/2440/102554A measurement of the parity-violating decay asymmetry parameter, alpha b, and the helicity amplitudes for the decay Lambda0b ->J/psi(mu+mu -)Lambda0(p pi -) is reported. The analysis is based on 1400 Lambda0b and Lambda -bar0b baryons selected in 4.6fb -1 of proton-proton collision data with a center-of-mass energy of 7 TeV recorded by the ATLAS experiment at the LHC. By combining the Lambda0b and Lambda -bar0b samples under the assumption of CP conservation, the value of alpha b is measured to be 0.30+/-0.16(stat)+/-0.06(syst). This measurement provides a test of theoretical models based on perturbative QCD or heavy-quark effective theory.en© 2014 CERN, for the ATLAS Collaboration. Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published articles title, journal citation, and DOI.Journal article003001305310.1103/PhysRevD.89.0920090003366513000012-s2.0-8490200756585740