Understand
The process $e^- e^+ \to \tau^- \tau^+$ is of particular interest because the tau lepton polarisation can be reconstructed, allowing its chiral nature to be probed.
- This note reports on a study of the reconstruction of the di-tau final state at ILC-500, its selection and the reduction of backgrounds, the identification of the tau lepton's decay mode, and on the extraction of the tau leptons' polarisation.
- The performance of this analysis is studied in two models of the ILD detector, one larger (IDR-L) the other smaller (IDR-S), which differ in the outer radius of the TPC and of the subdetectors beyond, and in the magnetic field strength of the detector solenoid.
- We find that the high-mass tau-pair events in which at least one tau decays haronically can be selected with an efficiency of around 60%, with a remaining background from non-di-tau processes at the few-% level.