Precise measurement of the asymmetry parameter delta in muon decay

Highly polarized ..mu../sup +/ from the surface muon beam at TRIUMF have been analyzed by means of the muon-spin-rotation technique to determine the parity-violating muon decay asymmetry as a function of the daughter positron's momentum. The primary result is a determination of the muon decay parameter delta to high precision (delta = 0.7486 +- 0.0026(stat) +- 0.0028(sys)) consistent with the prediction delta = 0.75 of the standard model of weak interactions. The implications of this measurement for generalized four-fermion contact interaction models of muon decay are discussed. The data are also used to constrain the parameters in certain left-right-symmetric and supersymmetric extensions of the standard model, and to limit the existence of lepton-number-violating scalar decays of the muon (..mu -->..esigma, where m(sigma)