Measuring CP Violation in $h \to \tau^+ \tau^-$ at Colliders

Understand

We investigate the LHC and Higgs Factory prospects for measuring the CP phase in the Higgs-tau-tau coupling.

• Currently this phase can be anywhere between 0 degrees (CP even) and 90 degrees (CP odd).
• A new, ideal observable is identified from an analytic calculation for the $\tau^\pm \to \rho^\pm\nu \to \pi^\pm \pi^0 \nu$ channel.
• It is demonstrated to have promising sensitivity at the LHC and superior sensitivity at the ILC compared to previous proposals.