Measurement of the Michel Parameter for Leptonic Tau Decay

This thesis (done under the supervision of Prof. John Matthews) uses data accumulated by the Mark II detector at the PEP storage ring to measure the Michel parameter (rho) for leptonic tau decays. This is done by fitting to e and mu momentum spectra from tau decays, as in previous measurements; in addition, the |p(e) times p(mu ) |^ectrum, accumulated from e mu tau pair events, is used to fit for rho. The fitted values of rho are 1.022 +/- 0.132 +/- 0.070 for the fit to the p(e) spectrum, 0.584 +/- 0.155 +/- 0.094 for p(mu), 0.814 +/- 0.244 +/- 0.164 for |p(e) times p(mu ) |, and 0.851 +/- 0.095 +/- 0.078 for a global fit to all three spectra. These values are consistent with a V - A tau decay coupling, and strongly exclude V + A. Tau production and decay is simulated with the most recent version of the KORALZ Monte Carlo program, which includes not only initial and final state radiative corrections to e^{+} e^{-}totau^{+ }tau^{-}, but radiative corrections to tau decay as well.