The TWIST experiment (TRIUMF weak interaction symmetry test)

The TRIUMF Weak Interaction Symmetry Test (TWIST) experiment aims at a precision measurement of the energy spectrum and of the angular distribution of the decay positrons from highly polarized muons. The experiment has been designed to reach a precision of a few parts in 10−4 for the so-called Michel parameters which are used to parametrize these distributions. After an engineering run in the fall of 2001, the current data taking phase should provide intermediate results for the ϱ and δ parameters at the 10−3 level by the end of 2003 which will be used to place largely model independent constraints on new physics beyond the Standard Model. A review of the status of the experiment is presented.