## Short description.

__Physics Motivation:__ measure the coupling between Z and left handed tau, and the coupling between Z and right handed tau. This is going to be very useful to constrain some of the contact interactions, or to test models such as gauge-Higgs unification.

__Search Channel:__ e+e- → tau tau, tau → 1-prong / 3-prong, Ecm = 500 GeV.

__Detector Benchmark:__ highly boosted tau reconstruction; in 3-prong channel, interesting to test the limit of track separation; in 1-prong channel, interesting to test PFA performance.

## Main observables.

__final observables:__ gL, gR, (for Ztautau couplings); cross section for e+e- → tau_L tau_R / tau_R tau_L.

__intermediate observables:__ efficiency of tau reconstruction, efficiency of tau decay mode identification, tau polarization

## plots for IDR

### current note (8 May)

## previous note (as of 27 March 2019)

## People.

Daniel Jeans and Keita Yumino, reviewed by Mikael Berggren

## References.

Daniel Jeans, “h->tau tau” [LCWS16, ILD0418]

S. Kawada et al., "A study of the measurement precision of the Higgs boson decaying into tau pairs at the ILC", https://arxiv.org/abs/1509.01885