Precise measurement of parity violation in polarized muon decay
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Abstract
We present a new high precision measurement of parity violation in the weak interaction, using polarized muon decay. The TWIST Collaboration has measured ${P}_{\ensuremath{\mu}}^{\ensuremath{\pi}}\ensuremath{\xi}$, where ${P}_{\ensuremath{\mu}}^{\ensuremath{\pi}}$ is the polarization of the muon in pion decay and $\ensuremath{\xi}$ describes the intrinsic asymmetry in muon decay. We find ${P}_{\ensuremath{\mu}}^{\ensuremath{\pi}}\ensuremath{\xi}=1.000\text{ }84\ifmmode\pm\else\textpm\fi{}0.000\text{ }29(\mathrm{stat}.{)}_{\ensuremath{-}0.000\text{ }63}^{+0.001\text{ }65}(\mathrm{syst}.)$, in good agreement with the standard model prediction of ${P}_{\ensuremath{\mu}}^{\ensuremath{\pi}}=\ensuremath{\xi}=1$. 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.