3 research outputs found
Measurement of the Positive Muon Anomalous Magnetic Moment to 0.46 ppm
We present the first results of the Fermilab Muon g-2 Experiment for the
positive muon magnetic anomaly . The anomaly is
determined from the precision measurements of two angular frequencies.
Intensity variation of high-energy positrons from muon decays directly encodes
the difference frequency between the spin-precession and cyclotron
frequencies for polarized muons in a magnetic storage ring. The storage ring
magnetic field is measured using nuclear magnetic resonance probes calibrated
in terms of the equivalent proton spin precession frequency
in a spherical water sample at 34.7C. The
ratio , together with known fundamental
constants, determines
(0.46\,ppm). The result is 3.3 standard deviations greater than the standard
model prediction and is in excellent agreement with the previous Brookhaven
National Laboratory (BNL) E821 measurement. After combination with previous
measurements of both and , the new experimental average of
(0.35\,ppm) increases the
tension between experiment and theory to 4.2 standard deviationsComment: 10 pages; 4 figure
Detailed Report on the Measurement of the Positive Muon Anomalous Magnetic Moment to 0.20 ppm
We present details on a new measurement of the muon magnetic anomaly, . The result is based on positive muon data taken at Fermilab's Muon Campus during the 2019 and 2020 accelerator runs. The measurement uses GeV polarized muons stored in a -m-radius storage ring with a T uniform magnetic field. The value of is determined from the measured difference between the muon spin precession frequency and its cyclotron frequency. This difference is normalized to the strength of the magnetic field, measured using Nuclear Magnetic Resonance (NMR). The ratio is then corrected for small contributions from beam motion, beam dispersion, and transient magnetic fields. We measure (0.21 ppm). This is the world's most precise measurement of this quantity and represents a factor of improvement over our previous result based on the 2018 dataset. In combination, the two datasets yield (0.20 ppm). Combining this with the measurements from Brookhaven National Laboratory for both positive and negative muons, the new world average is (exp) (0.19 ppm)