Improved Measurement of the Positive-Muon Lifetime and Determination of the Fermi Constant

摘要

The mean life of the positive muon has been measured to a precision of 11 ppm using a low-energy, pulsed muon beam stopped in a ferromagnetic target, which was surrounded by a scintillator detector array. The result, τ_μ = 2.197013(24) μs, is in excellent agreement with the previous world average. The new world average τ_μ = 2.197 019(21) μs determines the Fermi constant G_F = 1.166371(6) X 10~(-5) GeV~(-2) (5 ppm). Additionally, the precision measurement of the positive-muon lifetime is needed to determine the nucleon pseudoscalar coupling g_P.