Higgs CP properties using the τ decay modes at the ILC

We investigate the prospects of determining the CP nature of the 126 GeV neutral spin-0 (Higgs) boson h, discovered at the LHC, at a future linear e+e− collider (ILC). We consider the production of h by the Higgsstrahlung process e+e−→Z+h and its subsequent decays to τ leptons, h→τ−τ+. We investigate how precisely a possible pseudoscalar component of h can be detected by the measurement of a suitably defined angular distribution, if all major decay modes of the τ lepton are used. From our numerical simulations, we estimate the expected precision to the scalar-pseudoscalar mixing angle ϕ, including estimates of the background and of measurement uncertainties, to be Δϕ≃2.8° for Higgs-boson production at a center-of-mass energy of 250 GeV and for a collider with integrated luminosity of 1 ab−1.