Abstract:
We investigate the LHC 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 τ±→ρ±ν→π±π0ν channel. It is demonstrated to have promising sensitivity at the LHC and superior sensitivity compared to previous proposals. Our observable requires the reconstruction of the internal substructure of decaying taus but does not rely on measuring the impact parameter of tau decays. It is the first proposal for such a measurement at the LHC. For the 14 TeV LHC, we estimate that about 1 ab−1 data can discriminate CP-even versus CP-odd at the 5σ level. With 3 ab−1, the CP phase should be measurable to an accuracy of ∼11 degrees. We also compare to an e+e- Higgs Factory measurement, where we project that a 250 GeV run with 1 ab−1 luminosity can measure the phase to ∼4.4 degrees accuracy.
