A method to determine the electroweak mixing angle from Z decays to τ leptons using optimal observables

We propose a new method to measure the electroweak mixing angle in Z decays to τ leptons. For various τ decay channels optimal observables are constructed which yield the largest possible signal-to-noise ratio. These optimal observables are derived from the full spin-density-matrix of the process including correlations between τ spins and an approximation to the τ flight direction. (author)