The proposed FCC-ee collider provides optimal conditions for ultimate statstics studies of the
four heaviest particles of the Standard Model, the Z, W and Higgs bosons and the top quark.
With the phenomenal sample of 5x10^12 Z decays in the very clean e+e- environment it also
provides optimal conditions for precision studies of heavy flavour, among that studies of the
tau lepton. Possibilities are opened of much improved determinations of τ-lepton properties and,
via the measurement of the τ polarisation, of the neutral-current couplings of electrons and τs.
Improved measurements of τ-lepton properties – lifetime, leptonic branching fractions, and mass –
allow important tests of lepton universality. The experimental challenge is to match as far as
possible statistical uncertainties at the 10−5 level. This applies in particular to the lifetime
measurement, and to the branching fraction and polarisation measurements, where the cross-channel
contamination is of particular concern. These issues raise strict requirements, in particular, on
the accuracy of the construction and alignment of the vertex detector and of the precise calorimetric
separation and measurement of photons and π0s in the collimated τ decay topologies.
The talk will review the status of the FCC-ee project and summarise the opportunities for ultimate
precision tau-lepton measurements.