Precision muon decay measurements and improved constraints on the weak interaction
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abstract
The TWIST Collaboration has completed its measurement of the three muon decay parameters , , and P . This paper describes our determination of , which governs the shape of the overall momentum spectrum, and , which controls the momentum dependence of the parity-violating decay asymmetry. The results are =0.749770. 00012(stat)0.00023(syst) and =0.750490.00021(stat) 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 , , and P 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. 2012 American Physical Society.