Determination of the polarization of the decay positrons in polarized muon decay

The standard model of electroweak interactions predicts that the positrons from the decay of polarized positive muons are mainly longitudinally polarized. The measurement of the two transverse polarization components of the positron P-T1 and P-T2 is a sensitive tool to look for contributions from additional, exotic interactions and for the violation of time reversal invariance in this purely leptonic decay. The mu(PT)-experiment at the Paul Scherrer Institute determines the three positron polarization components simultaneously with the same apparatus by making use of three different effects. By examining the temporal dependence of annihilation-in-flight of the decay positrons with polarized electrons a possible non-zero value of the transverse polarization is determined. The phase of this transverse polarization can be measured by making use of the decay asymmetry. Using the dependence of annihilation-in-flight on the angle between electron polarization and positron momentum leads to the determination of the longitudinal polarization which not only completes the measurement of the entire polarization vector but also serves as a sensitivity check. In order to deduce the polarization at the time and location of the muon decay a method based on Monte-Carlo simulations with full spin-dependence implemented is being developed.