Precision muon decay measurements and improved constraints on the weak interaction

The TWIST Collaboration has completed its measurement of the three muon decay parameters rho, delta, and P-mu xi. This paper describes our determination of rho, which governs the shape of the overall momentum spectrum, and delta, which controls the momentum dependence of the parity-violating decay asymmetry. The results are rho = 0.749 77 +/- 0.000 12(stat) +/- 0.000 23(syst) and delta = 0.750 49 +/- 0.000 21(stat) +/- 0: 000 27(syst). These are consistent with the value of 3/4 given for both parameters in the standard model, and each is over a factor of 10 more precise than the measurements published prior to TWIST. Our final results on rho, delta, and P-mu xi have been incorporated into a new global analysis of all available muon decay data, resulting in improved model-independent constraints on the possible weak interactions of right-handed particles.