Measurement of the positive muon lifetime and determination of the Fermi constant to part-per-million precision

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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 2×1012 decays. Two different stopping target configurations were employed in independent data-taking periods. The combined results give τμ+(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: GF(MuLan)=1.1663788(7) ×10-5GeV-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 gP. © 2011 American Physical Society.

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