Magnetic-Field Measurement and Analysis for the Muon g-2 Experiment at Fermilab
Abstract
The Fermi National Accelerator Laboratory (FNAL) Muon
g − 2 Experiment
has measured the anomalous precession frequency
aμ ≡ (gμ − 2) /2
of the muon to a combined precision of 0.46 parts per million with data collected
during its first physics run in 2018. This paper documents the measurement of
the magnetic field in the muon storage ring. The magnetic field is monitored
by systems and calibrated in terms of the equivalent proton spin precession
frequency in a spherical water sample at 34.7 °C. The measured field is
weighted by the muon distribution resulting in
ωp',
the denominator in the ratio
ωa /ωp'
that together with known fundamental constants yields
aμ. The reported
uncertainty on
ωp'
for the Run-1 data set is 114 ppb consisting of uncertainy
contributions from frequency extraction, calibration, mapping, tracking, and
averaging of 56 ppb, and contributions from fast transient fields of 99 ppb.
Muon g-2 Collaboration,
Physical Review A, 103 (2021) 042208.
DOI: 10.1103/PhysRevA.103.042208
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