Measurement of the Positive Muon Lifetime and Determination of the Fermi Constant to Part-per-Million Precision

Abstract

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 × 10 12 decays. Two different stopping target configurations were employed in independent data-taking periods. The combined results give τ µ + (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 −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 .

Next-to-leading order prediction for the decay μ → e e + e − ν ν ¯ $$ \mu \to e\kern0.22em \left({e}^{+}{e}^{-}\right)\;\nu \kern0.2em \overline{\nu} $$

“…2) where G F = 1.166 378 7(6) × 10 −5 GeV −2 [34] is the Fermi constant, defined from the muon lifetime, and α = 1/137.035 999 157 (33) is the fine-structure constant [35,36]. Calling m µ and m e the masses of the muon and the electron (neutrinos are considered to be massless), we define the ratio r = m e /m µ .…”

LSND/MiniBooNe excess events and heavy neutrino fromμandKdecays

“…Very recently, the MuLan Collaboration has reported on measurements of the mean lifetime of positive muons to a precision of 0.6 ppm [24]. Using the new world average, ¼ 2:1969803ð22Þ s and the relation between the muon lifetime and the Fermi constant…”

“…where Á is the sum of phase space, QED and hadronic corrections, results in new determination of the Fermi constant G F ¼ 1:1663788ð7Þ Â 10 À5 GeV À2 to a precision of 0.6 ppm [24]. The mixing of the h into would decrease the determined value of G F .…”

Measurement of the Inclusive Electron Cross-Section from Heavy-Flavour Decays and Search for Compressed Supersymmetric Scenarios with the ATLAS Experiment

“…The theory was motivated by the earlier postulation of the neutrino in 1927 by Pauli to explain the continuous and , are spinors associated with the fermions of the interaction. The value of the constant G F can be obtained for example from measurements of the muon lifetime [8,9]. However, the form of the Lagrangian of equation 2.18 is not complete since it does not account for the parity violating nature of the weak interactions, which was first suspected by Lee and Yang [10] and then experimentally confirmed by Wu et al in 1956 [11].…”