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.
We report the result of a measurement of the positive muon lifetime τμ to one part-per-million (ppm) by the MuLan collaboration using a low-energy pulsed muon beam and a segmented array of plastic ...scintillators to record over 2×1012 decay positrons. Two different in-vacuum muon-stopping targets were used in separate data-taking periods. The combined result gives τμ+(MuLan)=2196980.3(2.2)ps(1ppm). This measurement of the muon lifetime provides the most precise determination of the Fermi constant, GF(MuLan)=1.1663788(7)×10−5 GeV−2(0.6 ppm), and will be used to extract the capture rates of the negative muon on the proton and the deuteron in the ongoing MuCap and MuSun experiments.
A compact and fast electromagnetic calorimeter prototype was designed, built, and tested in preparation for a next-generation, high-rate muon g-2 experiment. It uses a simple assembly procedure: ...alternating layers of 0.5-mm-thick tungsten plates and 0.5-mm-diameter plastic scintillating fiber ribbons. This geometry leads to a detector having a calculated radiation length of 0.69 cm, a Moliere radius of 1.73 cm, and a measured intrinsic sampling resolution term of (11.8\pm1.1)/\sqrt{E(GeV)}, in the range 1.5 to 3.5 GeV. The construction procedure, test beam results, and GEANT-4 comparative simulations are described.
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.
We propose to measure the rate \Rd\ for muon capture on the deuteron to better than 1.5% precision. This process is the simplest weak interaction process on a nucleus that can both be calculated and ...measured to a high degree of precision. The measurement will provide a benchmark result, far more precise than any current experimental information on weak interaction processes in the two-nucleon system. Moreover, it can impact our understanding of fundamental reactions of astrophysical interest, like solar pp fusion and the \(\nu+d\) reactions observed by the Sudbury Neutrino Observatory. Recent effective field theory calculations have demonstrated, that all these reactions are related by one axial two-body current term, parameterized by a single low-energy constant. Muon capture on the deuteron is a clean and accurate way to determine this constant. Once it is known, the above mentioned astrophysical, as well as other important two-nucleon reactions, will be determined in a model independent way at the same precision as the measured muon capture reaction.
The MuCap experiment is a high-precision measurement of the rate for the basic electroweak process of muon capture, mu- + p -> n + nu . The experimental approach is based on an active target ...consisting of a time projection chamber (TPC) operating with pure hydrogen gas. The hydrogen has to be kept extremely pure and at a stable pressure. A Circulating Hydrogen Ultrahigh Purification System was designed at the Petersburg Nuclear Physics Institute (PNPI) to continuously clean the hydrogen from impurities. The system is based on an adsorption cryopump to stimulate the hydrogen flow and on a cold adsorbent for the hydrogen cleaning. It was installed at the Paul Scherrer Institute (PSI) in 2004 and performed reliably during three experiment runs. During several months long operating periods the system maintained the hydrogen purity in the detector on the level of 20 ppb for moisture, which is the main contaminant, and of better than 7 ppb and 5 ppb for nitrogen and oxygen, respectively. The pressure inside the TPC was stabilized to within 0.024% of 10 bar at a hydrogen flow rate of 3 standard liters per minute.
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.
Phys.Rev.Lett.99:032002,2007 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 difference between the measured $\mu^-$
disappearance rate in hydrogen and the world average for the $\mu^+$ 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 hyperfine singlet ground state of the $\mu p$ atom is
measured to be $\Lambda_S=725.0 \pm 17.4 s^{-1}$, from which the induced
pseudoscalar coupling of the nucleon, $g_P(q^2=-0.88 m_\mu^2)=7.3 \pm 1.1$, is
extracted. This result is consistent with theoretical predictions for $g_P$
that are based on the approximate chiral symmetry of QCD.
The
μLan experiment at the Paul Scherrer Institute will measure the lifetime of the positive muon with a precision of 1 ppm, giving a value for the Fermi coupling constant
G
F
at the level of 0.5 ...ppm. Meanwhile, by measuring the observed lifetime of the negative muon in pure hydrogen, the
μCap experiment will determine the rate of muon capture, giving the proton's pseudoscalar coupling
g
p
to 7%. This coupling can be calculated precisely from heavy baryon chiral perturbation theory and therefore permits a test of QCD's chiral symmetry.
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 difference between the measured \(\mu^-\) disappearance rate in hydrogen and the world average for the \(\mu^+\) 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 hyperfine singlet ground state of the \(\mu p\) atom is measured to be \(\Lambda_S=725.0 \pm 17.4 s^{-1}\), from which the induced pseudoscalar coupling of the nucleon, \(g_P(q^2=-0.88 m_\mu^2)=7.3 \pm 1.1\), is extracted. This result is consistent with theoretical predictions for \(g_P\) that are based on the approximate chiral symmetry of QCD.
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