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[en] The rate of nuclear muon capture by the proton has been measured using a new technique based on a time projection chamber operating in ultraclean, deuterium-depleted hydrogen gas, which is key to avoiding uncertainties from muonic molecule formation. The capture rate from the hyperfine singlet ground state of the μp atom was obtained from the difference between the μ^- disappearance rate in hydrogen and the world average for the μ⁺ decay rate, yielding Λ_S=725.0±17.4 s^-1, from which the induced pseudoscalar coupling of the nucleon, g_P(q²=-0.88m_μ²)=7.3±1.1, is extracted

[en] We report a measurement of the positive muon lifetime to a precision of 1.0 ppm; it is the most precise particle lifetime ever measured. The experiment used a time-structured, low-energy muon beam and a segmented plastic scintillator array to record more than 2x10¹² decays. Two different stopping target configurations were employed in independent data-taking periods. The combined results give τ_μ⁺(MuLan)=2 196 980.3(2.2) ps, more than 15 times as precise as any previous experiment. The muon lifetime gives the most precise value for the Fermi constant: G_F(MuLan)=1.166 378 8(7)x10^-5 GeV^-2 (0.6 ppm). It is also used to extract the μ^-p singlet capture rate, which determines the proton's weak induced pseudoscalar coupling g_P.

[en] 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=2.197 013(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=1.166 371(6)x10^-5 GeV^-2 (5 ppm). Additionally, the precision measurement of the positive-muon lifetime is needed to determine the nucleon pseudoscalar coupling g_P

[en] The aim of the μCap experiment is a 1% measurement of the singlet capture rate Λ_S for the basic electro-weak reaction μ + p ^→ n + ν_μ. This observable is sensitive to the weak form-factors of the nucleon, in particular to the induced pseudoscalar coupling constant g_P. It will provide a rigorous test of theoretical predictions based on the Standard Model and effective theories of QCD. The present method is based on high precision lifetime measurements of μ^- in hydrogen gas and the comparison with the free μ⁺ lifetime. The μ^- experiment will be performed in ultra-clean, deuterium-depleted H₂ gas at 10 bar. Low density compared to liquid H₂ is chosen to avoid uncertainties due to ppμ formation. A time projection chamber acts as a pure hydrogen active target. It defines the muon stop position in 3D and detects rare background reactions. Decay electrons are tracked in cylindrical wire-chambers and a scintillator array covering 75% of 4π.