Measuring the CP state of tau lepton pairs from Higgs decay at the ILC

TL;DR

This paper presents a simulation-based analysis to measure the CP properties of the Higgs boson via tau lepton decays at the ILC, aiming to detect potential deviations indicating new physics.

Contribution

It develops a detailed analysis method using full detector simulation to measure the Higgs CP state through tau decay correlations at the ILC.

Findings

CP mixing angle can be measured to 75 mrad precision

Analysis demonstrates feasibility of CP measurement with 2 ab^{-1} at 250 GeV

Method distinguishes CP-even and CP-odd components effectively

Abstract

In the Standard Model, the Higgs boson is a CP even state with CP conserving couplings; any deviations from this would be a sign of new physics. These CP properties can be probed by measuring Higgs decays to tau lepton pairs: the transverse correlation between the tau spins depends on CP. This paper develops such an analysis, using full simulation of signal and background events in the International Large Detector concept for the International Linear Collider. We consider Higgs-strahlung events e+ e- -> Z H) in which the Z boson decays to electrons, muons, or hadrons, and the Higgs boson decays to $\tau$ leptons, which then decay either to (pi+ nu) or (pi+ pi0 nu). Assuming 2 ab^{-1} of integrated luminosity at a center-of-mass energy of 250~GeV, the mixing angle psi_CP between even and odd CP components of the tau pair from Higgs boson decays can be measured to a precision of 75~mrad (4.3 deg).