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_muxi. 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=0.74977pm 0.00012(stat.)pm 0.00023(syst.) and delta = 0.75049pm 0.00021(stat.)pm 0.00027(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_muxi 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.