Wuppertal 2015 – scientific programme

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T: Fachverband Teilchenphysik

T 91: Higgs: Htautau (CP und Polarisierung)

T 91.7: Talk

Thursday, March 12, 2015, 18:15–18:30, M.10.12 (HS 14)

Study of τ-spin correlations for the DrellYan process pp→ Z^*/γ^*→τ⁺τ⁻ using the impact parameter method at ATLAS — •Maike Hansen, Philip Bechtle, Klaus Desch, Christian Grefe, and Peter Wagner for the ATLAS collaboration — Universität Bonn

After the discovery of a Higgs-like boson, that is compatible with the Standard Model Higgs boson, in 2012, the study of its CP-nature is an important task. In the H → τ⁺τ⁻ decay channel, the Higgs CP-properties can be measured based on the track impact parameter, as proposed by Stefan Berge et al. This method uses the angle φ_CP^* between the tau-decay planes, which is a CP-sensitive variable and can be derived from the track impact parameter in 1-prong tau-decays.

In the case of a CP-even or CP-odd Higgs state, the φ_CP^* variable shows a cosine-dependence. In contrast to that, in Z/ → τ⁺τ⁻ decays, which constitute the major irreducible background for a Higgs CP-measurement, it is expected to be flat. However, dividing the Z/ → τ⁺τ⁻ phase-space into two subsets: One set, where the momentum of the π⁻ from the tau-decay is preferably parallel and one where it is perpendicular to the production plane, an artificial cosφ_CP^*-dependence is introduced. This way, a φ_CP^* dependence can be measured also in Z → τ⁺τ⁻ events. Thus, from measuring the already known Z-Boson CP-state, systematic effects as well as the sensitivity on a Higgs CP-measurement can be understood.