A Precision Measurement of μ~+ Decay

摘要

TWIST (the TRIUMF Weak Interaction Symmetry Test) is an experiment to measure the energy and angular distributions of the positrons (e~+) emitted from the decay of polarized positive muons (μ~+). The distributions are described by four parameters ρ, η, δ, and ξ, widely referred to as the Michel parameters. The values of the four parameters are exactly predicted by the Standard Model; the goal of TWIST is to search for new physics that leads to deviations from the predictions by measuring ρ, δ, and Pμξ to a few parts in 10~4. This represents an improvement of more than one order of magnitude over the existing precision.