Jane Cummings

In this thesis, the first measurement of tau polarization at a hadron collider, and the first measurement of tau polarization in W boson decays to a tau and neutrino altogether, is presented.  The measurement of tau polarization is a test of the structure of the vector (V) and axial vector (A) couplings of the W boson to the third generation leptons.  Such a test is not possible with first and second generation leptons for which the helicity state is not accessible in a collider experiment.  The V-A structure of the charged current weak interaction at small W virtuality (Q^2) is well established from the kinematics of tau decays while the structure at Q^2 = m_W^2 had not been measured explicitly. In addition, an advanced analysis of the tau polarization in Z boson decays to tau pairs is presented.