Search for the Standard Model Higgs Boson and Test of CP Invariance in Vector-Boson Fusion Production of the Higgs Boson in the Fully Leptonic H->tautau->ll4nu Final State in Proton-Proton Collisions with the ATLAS Detector at the LHC

Results of a search for fully leptonic H->tautau->ll4nu decays are presented, based on the set of proton–proton collision data recorded by the ATLAS experiment at the LHC during 2012. The data corresponds to an integrated luminosity of 20.3 fb^-1 at the centre-of-mass energy of sqrt(s)=8 TeV. An excess of events over the expected background from other Standard Model processes is found. The observed (expected) significance is 2.7 (1.3) standard deviations. The measured signal strength, normalised to the Standard Model expectation, is mu =2.1+1.0-0.8. This is consistent with the predicted Yukawa coupling strength in the Standard Model. The analysis contributes to the combined search for H->tautau including also the fully hadronic and semi-leptonic final states. The combined analysis provides evidence for the direct coupling of the Higgs boson to fermions with the observed (expected) significance of 4.5 (3.4) standard deviations. Furthermore a test of CP invariance in Higgs boson production via vector-boson fusion is presented. This test uses CP-odd observables such as the method of the Optimal Observable. The CP analysis is based on the above search for H->tautau->ll4nu decays. 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 dtilde. The measured mean values and distributions of the CP-odd observables agree with the expectation in the Standard Model and show no sign of CP violation. The CP-mixing parameter dtilde is constrained to the central confidence interval [−0.03, 0.17] at 68% confidence level. This is consistent with the Standard Model expectation of dtilde=0. The analysis contributes to a combined analysis including also semi-leptonic final states, which provides a measured confidence interval on the dtilde parameter of [-0.11, 0.05] at 68% confidence level. Overall, no hints to physics beyond the Standard Model are observed.