Measurement of the Muon Decay Parameter delta
  The muon decay parameter delta has been measured by the TWIST collaboration. We find delta = 0.74964 +- 0.00066(stat.) +- 0.00112(syst.), consistent with the Standard Model value of 3/4. This result implies that the product Pmuxi of the muon polarization in pion decay, Pmu, and the muon decay parameter xi falls within the 90% confidence interval 0.9960 < Pmuxi < xi < 1.0040. It also has implications for left-right-symmetric and other extensions of the Standard Model. 
TWIST Collaboration: A. Gaponenko, R. Bayes, Yu.I. Davydov, P.   Depommier, J. Doornbos, W. Faszer, M.C. Fujiwara, C.A. Gagl...