Measurement of Pμξ in polarized muon decay

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 2 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.