Measurement of the Muon Decay Spectrum with a Wire Spark-Chamber Spectrometer

The decay spectrum of the positive muon has been studied in a wire spark-chamber spectrometer of wide momentum acceptance. Both the parameters δ and ρ were determined. On the basis of 4.9×{}10⁵ events, obtained in runs with different fields and targets, we find for the parameter governing the energy dependence of the asymmetry, the value δ=0.752±0.009. From a spectrum of 1.7×{}10⁵ events we find for the shape parameters of the isotropic spectrum ρ=0.762±0.008 (assuming η≡0), or η=-0.7±0.5 (assuming ρ≡3/4). These values for ρ and δ are in agreement with two-component neutrino theory. Using our value of δ and averages of the most accurate published values of the other muon decay parameters, we find that the scalar and tensor couplings (in charge retention ordering) can still account for as much as 30% of the interaction.