Final PhD Oral Examination (Thesis Title: “Precise Measurement of Rare Pion Decay”)

Abstract: A precise measurement of the pion to positron or muon decay branching ratio provides a test of lepton universality incorporated in the Standard Model (SM) of particle physics. If a measurement is consistent with the SM, new constraints could be set on new physics. Most remarkably, a deviation could imply the presence of a new pseudo-scalar interaction whose energy scales up to O(1000 TeV) would enhance the branching ratio by O(0.1%). In some instances, these constraints can far exceed the reach of direct searches at colliders. This dissertation represents the latest experimental measurement effort by the PIENU collaboration. The current analysis presented in this thesis is blinded but includes the highest quality data portion available of around 3M  π → e ν events. Furthermore, major experimental systematic problems have been solved, allowing for increased precision up to 0.12% in the branching ratio and up to 0.06% in test of lepton universality.