Measurement of P_{mu}xi 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 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. 
TWIST Collaboration: B. Jamieson, R. Bayes, Yu.I. Davydov, P.   Depommier, J. Doornbos, W. Faszer, M.C. Fujiwara, C.A. Gagli...