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UBC Theses and Dissertations

Measurement of the muon decay asymmetry parameter with the TWIST spectrometer Jamieson, Blair


Muon decay, a purely leptonic decay, is a relatively simple interaction to study when looking for physics not explained by the standard theory of electroweak interactions. In particular, the muon decay asymmetry parameter is directly related to the degree to which weak interactions violate parity, or mirror, symmetry. At the Tri-University Meson Facility (TRIUMF), the TRIUMF Weak Interaction Symmetry Test (TWTST) spectrometer was used to measure the energy and angle spectrum of decay positrons from muon decay. By measuring a large part of the muon decay spectrum, TWXST can simultaneously determine three of the muon decay parameters with a high degree of accuracy. This thesis presents the first direct TWIST measurement of the muon decay asymmetry parameter PM£ which was determined to be 1.0003 ±0.0006(stat) ±0.0038(syst). The uncertainty on this measurement is a factor of two lower than a previous direct measurement. This measurement is consistent with the standard model of particle physics, and further constrains physics beyond the standard model.

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