PT Journal AU ATLAS Collaboration (Aad, Gea Alvarez Piqueras, D Barranco Navarro, L Cabrera Urban, S Castillo Gimenez, V Cerda Alberich, L Costa, MJ Fernandez Martinez, P Ferrer, A Fiorini, L Fuster, J Garcia, C Garcia Navarro, JE Gonzalez de la Hoz, S Hernandez Jimenez, Y Higon-Rodriguez, E Irles Quiles, A Jimenez Pena, J King, M Lacasta, C Lacuesta, VR Marti-Garcia, S Mitsou, VA Pedraza Lopez, S Rodriguez Rodriguez, D Romero Adam, E Ros, E Salt, J Sanchez Martinez, V Soldevila, U Sanchez, J Valero, A Valls Ferrer, JA Vos, M TI Test of CP invariance in vector-boson fusion production of the Higgs boson using the Optimal Observable method in the ditau decay channel with the ATLAS detector SO European Physical Journal C JI Eur. Phys. J. C PY 2016 BP 658 - 25pp VL 76 IS 12 DI 10.1140/epjc/s10052-016-4499-5 LA English AB A test of CP invariance in Higgs boson production via vector-boson fusion using the method of the Optimal Observable is presented. The analysis exploits the decay mode of the Higgs boson into a pair of t leptons and is based on 20.3 fb(-1) of proton-proton collision data at root s = 8 TeV collected by the ATLAS experiment at the LHC. Contributions from CP-violating interactions between the Higgs boson and electroweak gauge bosons are described in an effective field theory framework, in which the strength of CP violation is governed by a single parameter (d) over tilde. The mean values and distributions of CP-odd observables agree with the expectation in the Standard Model and show no sign of CP violation. The CP-mixing parameter (d) over tilde is constrained to the interval (-0.11, 0.05) at 68% confidence level, consistent with the Standard Model expectation of (d) over tilde = 0. ER