Measurement of the Michel rho parameter in direct muon decay

We report on the status of LAMPF experiment E-1240 to measure the Michel ρ parameter in direct muon decay. This experiment ran in 1993, and the data are currently being analyzed. The expected precision on the ρ parameter is ±0.0008. This result will provide better constraints on new physics, particularly on the charged vector bosons’ mixing angle ζ in the manifestly left-right symmetric extension of the Standard Model.