A test of CP invariance in Higgs boson production via vector-boson fusion is performed in the H→ττ decay channel. This test uses the Optimal Observable method and is carried out using 36.1fb−1 of s=13TeV proton–proton collision data collected by the ATLAS experiment at the LHC. Contributions from CP-violating interactions between the Higgs boson and electroweak gauge bosons are described by an effective field theory, in which the parameter d˜ governs the strength of CP violation. No sign of CP violation is observed in the distributions of the Optimal Observable, and d˜ is constrained to the interval [−0.090, 0.035] at the 68% confidence level (CL), compared to an expected interval of d˜∈[−0.035,0.033] based upon the Standard Model prediction. No constraints can be set on d˜ at 95% CL, while an expected 95% CL interval of d˜∈[−0.21,0.15] for the Standard Model hypothesis was expected.

Aad, G., Abbott, B., Abbott, D.C., Abed Abud, A., Abeling, K., Abhayasinghe, D.K., et al. (2020). Test of CP invariance in vector-boson fusion production of the Higgs boson in the H → ττ channel in proton–proton collisions at [Formula presented] with the ATLAS detector. PHYSICS LETTERS. SECTION B, 805, 135426 [10.1016/j.physletb.2020.135426].

Test of CP invariance in vector-boson fusion production of the Higgs boson in the H → ττ channel in proton–proton collisions at [Formula presented] with the ATLAS detector

D'Amico V.;Di Micco B.;Di Nardo R.;Martinelli L.;Orestano D.;