Helicity of Electrons fromμ−Decay

The helicity of electrons from ${\mu }^{-}$ decay has been measured using the spin dependence of electron-electron (Møller) scattering. A magnetized foil (Supermendur) was used as a target of polarized electrons. Optical spark chambers, scintillators, and decision-making spark chambers were used to detect the scattering events, and the pictures were measured with an automatic film scanning system (Chloe). The experimental method and the data processing system reduced the systematic error due to background events below that of previous experiments. The helicity was found to be -0.89±0.28.