Mulan: a part-per-million measurement of the muon lifetime and determination of the Fermi constant

Journal Article · Mon Sep 06 00:00:00 EDT 2021 · SciPost Physics Proceedings

DOI:https://doi.org/10.21468/SciPostPhysProc.5.016· OSTI ID:1819006

Carey, Rebecca ^[1]; Gorringe, Tim ^[2]; Hertzog, David ^[3]

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1. Boston University
2. University of Kentucky
3. University of Washington

The part-per-million measurement of the positive muon lifetime and determination of the Fermi constant by the MuLan experiment at the Paul Scherrer Institute is reviewed. The experiment used an innovative, time-structured, surface muon beam and a near-4 \pi $\pi$ , finely-segmented, plastic scintillator positron detector. Two in-vacuum muon stopping targets were used: a ferromagnetic foil with a large internal magnetic field, and a quartz crystal in a moderate external magnetic field. The experiment acquired a dataset of 1.6 \times 10^{12} $1.6\times {10}^{12}$ positive muon decays and obtained a muon lifetime \tau_{\mu} = 2\, 196\, 980.3(2.2) ${\tau }_{\mu }=2196980.3\left(2.2\right)$ ~ps (1.0~ppm) and Fermi constant G _F = 1.166\, 378\, 7(6) \times 10^{-5} ${}_F=1.1663787\left(6\right)\times {10}^{-5}$ GeV ^{-2} ${}^{-2}$ (0.5~ppm). The thirty-fold improvement in \tau_{\mu} ${\tau }_{\mu }$ has proven valuable for precision measurements in nuclear muon capture and the commensurate improvement in G _F ${}_F$ has proven valuable for precision tests of the standard model.

• Sponsoring Organization: USDOE
• Grant/Contract Number: FG02-97ER41020
• OSTI ID: 1819006
• Journal Information: SciPost Physics Proceedings, Journal Name: SciPost Physics Proceedings Journal Issue: 5; ISSN 2666-4003
• Publisher: Stichting SciPost
• Country of Publication: Netherlands
• Language: English