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jan10-offprint-macdonald.pdf

The TWIST experiment is a high-precision study of the weak interaction, examining billions of muon decays to look for evidence for interactions not predicted by the Standard Model of particle physics. The spectrum of muon decays can be described by a set of decay parameters whose values depend on the fundamental nature of the weak interaction. This work presents TWIST’s intermediate measurements of the decay parameters ρ and δ, which strengthened the Standard Model’s predictions and significantly tightened the constraints these parameters place on competing theories.