A precision measurements of the Michel parameter in polarized muon decay

The weak interaction Mitchel parameter ε11 is known only with poor precision. The present relative freedom of this parameter allows several interesting extensions to the Standard Model. Likewise, a precision measure of this parameter would add constraints to any Standard Model extensions. The longitudinal polarization of positrons emitted near the energy end point in the direction opposite to the polarization of the decaying muon is very sensitive to the ε11 parameter. We have proposed a relative measurement which takes advantage of this sensitivity. Details of the positron spectrometer, the energy identification using a tracker based on double sided silicon strip detectors, and the positron polarization measurement using both annihilation-in-flight and Bhabha scattering will be discussed. (author)