Precise Measurement of the ParameterδGoverning the Decay Spectrum of Polarized Muons

A precision measurement of the energy dependence of the asymmetry of the decay of the positive muon has been made with a wire spark-chamber spectrometer of large momentum acceptance. We find, as an average of runs at different fields and with different targets, $\delta =0.758\mathrm{}\pm 0.010$, in agreement with the two-component neutrino theory.