15 research outputs found
Measurement of the Positive Muon Anomalous Magnetic Moment to 0.20 ppm
We present a new measurement of the positive muon magnetic anomaly, a_{μ}≡(g_{μ}-2)/2, from the Fermilab Muon g-2 Experiment using data collected in 2019 and 2020. We have analyzed more than 4 times the number of positrons from muon decay than in our previous result from 2018 data. The systematic error is reduced by more than a factor of 2 due to better running conditions, a more stable beam, and improved knowledge of the magnetic field weighted by the muon distribution, ω[over ˜]_{p}^{'}, and of the anomalous precession frequency corrected for beam dynamics effects, ω_{a}. From the ratio ω_{a}/ω[over ˜]_{p}^{'}, together with precisely determined external parameters, we determine a_{μ}=116 592 057(25)×10^{-11} (0.21 ppm). Combining this result with our previous result from the 2018 data, we obtain a_{μ}(FNAL)=116 592 055(24)×10^{-11} (0.20 ppm). The new experimental world average is a_{μ}(exp)=116 592 059(22)×10^{-11} (0.19 ppm), which represents a factor of 2 improvement in precision
Measurement of the anomalous precession frequency of the muon in the Fermilab Muon g-2 Experiment
The Muon g-2 Experiment at Fermi National Accelerator Laboratory (FNAL) has
measured the muon anomalous precession frequency to an uncertainty
of 434 parts per billion (ppb), statistical, and 56 ppb, systematic, with data
collected in four storage ring configurations during its first physics run in
2018. When combined with a precision measurement of the magnetic field of the
experiment's muon storage ring, the precession frequency measurement determines
a muon magnetic anomaly of (0.46 ppm). This article describes the multiple techniques employed
in the reconstruction, analysis and fitting of the data to measure the
precession frequency. It also presents the averaging of the results from the
eleven separate determinations of \omega_a, and the systematic uncertainties on
the result.Comment: 29 pages, 19 figures. Published in Physical Review
Beam dynamics corrections to the Run-1 measurement of the muon anomalous magnetic moment at Fermilab
This paper presents the beam dynamics systematic corrections and their uncertainties for the Run-1 data set of the Fermilab Muon g-2 Experiment. Two corrections to the measured muon precession frequency are associated with well-known effects owing to the use of electrostatic quadrupole (ESQ) vertical focusing in the storage ring. An average vertically oriented motional magnetic field is felt by relativistic muons passing transversely through the radial electric field components created by the ESQ system. The correction depends on the stored momentum distribution and the tunes of the ring, which has relatively weak vertical focusing. Vertical betatron motions imply that the muons do not orbit the ring in a plane exactly orthogonal to the vertical magnetic field direction. A correction is necessary to account for an average pitch angle associated with their trajectories. A third small correction is necessary because muons that escape the ring during the storage time are slightly biased in initial spin phase compared to the parent distribution. Finally, because two high-voltage resistors in the ESQ network had longer than designed RC time constants, the vertical and horizontal centroids and envelopes of the stored muon beam drifted slightly, but coherently, during each storage ring fill. This led to the discovery of an important phase-acceptance relationship that requires a correction. The sum of the corrections to is 0.50 0.09 ppm; the uncertainty is small compared to the 0.43 ppm statistical precision of
Magnetic Field Measurement and Analysis for the Muon g-2 Experiment at Fermilab
The Fermi National Accelerator Laboratory has measured the anomalous precession frequency 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 nuclear magnetic resonance systems and calibrated in terms of the equivalent proton spin precession frequency in a spherical water sample at 34.7C. The measured field is weighted by the muon distribution resulting in , the denominator in the ratio / that together with known fundamental constants yields . The reported uncertainty on for the Run-1 data set is 114 ppb consisting of uncertainty contributions from frequency extraction, calibration, mapping, tracking, and averaging of 56 ppb, and contributions from fast transient fields of 99 ppb
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
Beam dynamics corrections to the Run-1 measurement of the muon anomalous magnetic moment at Fermilab
This paper presents the beam dynamics systematic corrections and their uncertainties for the Run-1 data set of the Fermilab Muon g-2 Experiment. Two corrections to the measured muon precession frequency are associated with well-known effects owing to the use of electrostatic quadrupole (ESQ) vertical focusing in the storage ring. An average vertically oriented motional magnetic field is felt by relativistic muons passing transversely through the radial electric field components created by the ESQ system. The correction depends on the stored momentum distribution and the tunes of the ring, which has relatively weak vertical focusing. Vertical betatron motions imply that the muons do not orbit the ring in a plane exactly orthogonal to the vertical magnetic field direction. A correction is necessary to account for an average pitch angle associated with their trajectories. A third small correction is necessary because muons that escape the ring during the storage time are slightly biased in initial spin phase compared to the parent distribution. Finally, because two high-voltage resistors in the ESQ network had longer than designed RC time constants, the vertical and horizontal centroids and envelopes of the stored muon beam drifted slightly, but coherently, during each storage ring fill. This led to the discovery of an important phase-acceptance relationship that requires a correction. The sum of the corrections to is 0.50 0.09 ppm; the uncertainty is small compared to the 0.43 ppm statistical precision of
Comparison of disease progress curves for yam anthracnose (Colletotrichum gloeosporioides)
The straw tracking detector for the Fermilab Muon g-2 Experiment
The Muon Experiment at Fermilab uses a gaseous straw tracking detector
to make detailed measurements of the stored muon beam profile, which are
essential for the experiment to achieve its uncertainty goals. Positrons from
muon decays spiral inward and pass through the tracking detector before
striking an electromagnetic calorimeter. The tracking detector is therefore
located inside the vacuum chamber in a region where the magnetic field is large
and non-uniform. As such, the tracking detector must have a low leak rate to
maintain a high-quality vacuum, must be non-magnetic so as not to perturb the
magnetic field and, to minimize energy loss, must have a low radiation length.
The performance of the tracking detector has met or surpassed the design
requirements, with adequate electronic noise levels, an average straw hit
resolution of m, a detection efficiency of 97% or higher,
and no performance degradation or signs of aging. The tracking detector's
measurements result in an otherwise unachievable understanding of the muon's
beam motion, particularly at early times in the experiment's measurement period
when there are a significantly greater number of muons decaying. This is vital
to the statistical power of the experiment, as well as facilitating the precise
extraction of several systematic corrections and uncertainties. This paper
describes the design, construction, testing, commissioning, and performance of
the tracking detector.Comment: 37 pages, 27 figure