An upper limit on the #nu#_#tau# mass from #tau##->#3#pi#"+"/"-#nu#_#tau# decays

A new statistical approach to determine an upper limit for the mass of the #nu#_#tau# from #tau# #-># 3#pi#"+"/"-#nu#_#tau# decays has been applied to the data collected with the OPAL detector at LEP during the period 1990-1994. The limit is obtained using a method based on the comparision of the two-dimensional missing mass squared vs. missing energy distribution with those from different neutrino mass hypotheses. This approach makes explicit use of the reconstruction of the #tau# direction of flight. From a sample of 2514 selected #tau# #-># 3#pi#"+"/"-#nu#_#tau# decays an upper limit of 35.3 MeV at 95% confidence level has been obtained. Combining this result with OPAL's previously published measurement from #tau# #-># 5#pi#"+"/"-#nu#_#tau# decays a limit of 29.9 MeV at 95% confidence level was determined. (orig.)SIGLEAvailable from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

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

We propose a new method to measure the electroweak mixing angle in Z decays to tau leptons. For various tau 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 tau spins and an approximation to the tau flight direction. (orig.)24 refs.SIGLEAvailable from TIB Hannover: RN 5063(97-05) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman