Precise measurement of parity violation in polarized muon decay (vol 84, 032005, 2011)

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 = 1.000 84 +/- 0.000 29(stat:)(-0.001 63)(+0.000 63)(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.