  By exploiting the relatively long lifetime of the tau lepton, we propose
several novel methods for searching for new physics at an electron-positron
collider. We consider processes that involve final states consisting of a tau
lepton pair plus two missing particles. The mass and spin of the new physics
particles can be measured in 3-prong tau decays. The tau polarization, which
reflects the coupling to new physics, can be measured from the $\tau \to \pi
\nu$ decay channel using the impact parameter distribution of the charged pion.
We also discuss the corresponding backgrounds for these measurements, the
next-to-leading order (NLO) effects, and the implications of finite detector
resolution.
