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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=0.74977\pm 0.00012(stat.)\pm 0.00023(syst.) and \delta = 0.75049\pm 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_\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., Comment: 19 pages, 10 figures

We present a new high precision measurement of parity violation in the weak interaction, using polarized muon decay. The TWIST collaboration has measured $P_\mu^\pi \xi$, where $P_\mu^\pi$ is the polarization of the muon in pion decay and $\xi$ describes the intrinsic asymmetry in muon decay. We find $P_\mu^\pi \xi = 1.00084 \pm 0.00029\,(\textrm{stat.})_{-0.00063}^{+0.00165}\,(\textrm{syst.})$, in good agreement with the standard model prediction of $P_\mu^\pi=\xi=1$. Our result is a factor of 7 more precise than the pre-TWIST value, setting new limits in left-right symmetric electroweak extensions to the standard model., Comment: 18 pages, 12 figures, published in Phys. Rev. D

The TWIST collaboration has performed new measurements of two of the parameters that describe muon decay: $��$, which governs the shape of the overall momentum spectrum, and $��$, which governs the momentum dependence of the parity-violating decay asymmetry. This analysis gives the results $��=0.75014\pm 0.00017(\text{stat})\pm 0.00044(\text{syst})\pm 0.00011(��)$, where the last uncertainty arises from the correlation between $��$ and the decay parameter $��$, and $��= 0.75067\pm 0.00030(\text{stat})\pm 0.00067(\text{syst})$. These are consistent with the value of 3/4 given for both parameters in the Standard Model of particle physics, and are a factor of two more precise than the measurements previously published by TWIST. A new global analysis of all available muon decay data incorporating these results is presented. Improved lower and upper limits on the decay parameter $P_��^����$ of $0.99524 < P_��^����\leq ��< 1.00091$ at 90% confidence are determined, where $P_��^��$ is the polarization of the muon when it is created during pion decay, and $��$ governs the muon decay asymmetry. These results set new model-independent constraints on the possible weak interactions of right-handed particles. Specific implications for left-right symmetric models are discussed., 14 pages, 14 figs, accepted for publication in Phys. Rev. D

The quantity P_{mu}^{pi}xi, where xi is one of the muon decay parameters and $P_{\mu}^{\pi}$ is the degree of muon polarization in pion decay, has been measured. The value P_{mu}^{pi}xi = 1.0003 +- 0.0006 stat. +- 0.0038 syst. was obtained. This result agrees with previous measurements but is over a factor of two more precise. It also agrees with the Standard Model prediction for P_{mu}^{pi}xi and thus leads to restrictions on left-right symmetric models., Comment: 11 pages, 7 figures, Phys. Rev. D 74, 072007 (2006) Final version

The TWIST Collaboration has measured the Michel parameter $��$ in normal muon decay, $��^+ \to e^+ ��_e \bar��_��$. In the Standard Model, $��$ = 3/4. Deviations from this value require mixing of left- and right-handed muon and electron couplings in the muon-decay Lagrangian. We find $��$ = 0.75080 $\pm$ 0.00044(stat.) $\pm$ 0.00093(syst.) $\pm$ 0.00023, where the last uncertainty represents the dependence of $��$ on the Michel parameter $��$. This result sets new limits on the $W_L-W_R$ mixing angle in left-right symmetric models., 4 pages, 3 figures, submitted to PRL