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The aim of the MuCap experiment is a 1% measurement of the singlet capture rate Lambda_S for the basic electro-weak reaction mu + p -> n + nu_mu. 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 mu^- in hydrogen gas and the comparison with the free mu^+ lifetime. The mu^- experiment will be performed in ultra-clean, deuterium-depleted H_2 gas at 10 bar. Low density compared to liquid H_2 is chosen to avoid uncertainties due to ppmu formation. A time projection chamber acts as a pure hydrogen active target. It defines the muon stop position in 3-D and detects rare background reactions. Decay electrons are tracked in cylindrical wire-chambers and a scintillator array covering 75% of 4 pi. Comment: Int. RIKEN Conf. on Muon Catalyzed Fusion and Related Exotic Atoms, April 2001, Shimoda, Japan, to be published in Hyperfine Interactions

We present a detailed report of the method, setup, analysis and results of a precision measurement of the positive muon lifetime. The experiment was conducted at the Paul Scherrer Institute using a time-structured, nearly 100%-polarized, surface muon beam and a segmented, fast-timing, plastic scintillator array. The measurement employed two target arrangements; a magnetized ferromagnetic target with a ~4 kG internal magnetic field and a crystal quartz target in a 130 G external magnetic field. Approximately 1.6 x 10^{12} positrons were accumulated and together the data yield a muon lifetime of tau_{mu}(MuLan) = 2196980.3(2.2) ps (1.0 ppm), thirty times more precise than previous generations of lifetime experiments. The lifetime measurement yields the most accurate value of the Fermi constant G_F (MuLan) = 1.1663787(6) x 10^{-5} GeV^{-2} (0.5 ppm). It also enables new precision studies of weak interactions via lifetime measurements of muonic atoms., Comment: Submitted for publication in Phys. Rev. D (32 pages, 28 figures, 5 tables)

We report a measurement of the positive muon lifetime to a precision of 1.0 parts per million (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 2 x 10^{12} decays. Two different stopping target configurations were employed in independent data-taking periods. The combined results give tau_{mu^+}(MuLan) = 2196980.3(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) = 1.1663788 (7) x 10^-5 GeV^-2 (0.6 ppm). It is also used to extract the mu^-p singlet capture rate, which determines the proton's weak induced pseudoscalar coupling g_P., Accepted for publication in Phys. Rev. Lett

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, tau_mu = 2.197013(24) us, is in excellent agreement with the previous world average. The new world average tau_mu = 2.197019(21) us 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., As published version (PRL, July 2007)

The rate of nuclear muon capture by the proton has been measured using a new experimental technique based on a time projection chamber operating in ultra-clean, deuterium-depleted hydrogen gas at 1 MPa pressure. The capture rate was obtained from the dierence between the measured disappearance rate in hydrogen and the world average for the + decay rate. The target’s low gas density of 1% compared to liquid hydrogen is key to avoiding uncertainties that arise from the formation of muonic molecules. The capture rate from the hyperne singlet ground state of the p atom is measured to be S = 725:0 17:4 s 1 , from which the induced pseudoscalar coupling of the nucleon, g P (q 2 = 0:88m 2 ) = 7:3 1:1, is extracted. This result is consistent with theoretical predictions for gP that are based on the approximate chiral symmetry of QCD.