Precise measurement of parity violation in polarized muon decay

Abstract

We present a new high precision measurement of parity violation in the weak interaction, using polarized muon decay. The TWIST collaboration has measured $P_{\hat{I}}{¼}^{\ddot{I}}€\hat{I}¾$, where $P_{\hat{I}}{¼}^{\ddot{I}}€$ is the polarization of the muon in pion decay and $\hat{I}¾$ describes the intrinsic asymmetry in muon decay. We find $P_{\hat{I}}{¼}^{\ddot{I}}€\hat{I}¾=1.00084\pm 0.00029(\text{stat.}{)}_{-0.00063}^{+0.00165}(\text{syst.})$, in good agreement with the standard model prediction of $P_{\hat{I}}{¼}^{\ddot{I}}€=\hat{I}¾=1$. 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.

18 pages, 12 figures, published in Phys. Rev. D