8 research outputs found

    Measurement of the Positive Muon Anomalous Magnetic Moment to 0.46 ppm

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    We present the first results of the Fermilab Muon g-2 Experiment for the positive muon magnetic anomaly aÎŒâ‰Ą(gΌ−2)/2a_\mu \equiv (g_\mu-2)/2. 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 ωa\omega_a 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 ω~pâ€Č{\tilde{\omega}'^{}_p} in a spherical water sample at 34.7∘^{\circ}C. The ratio ωa/ω~pâ€Č\omega_a / {\tilde{\omega}'^{}_p}, together with known fundamental constants, determines aÎŒ(FNAL)=116 592 040(54)×10−11a_\mu({\rm FNAL}) = 116\,592\,040(54)\times 10^{-11} (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 ÎŒ+\mu^+ and Ό−\mu^-, the new experimental average of aÎŒ(Exp)=116 592 061(41)×10−11a_\mu({\rm Exp}) = 116\,592\,061(41)\times 10^{-11} (0.35\,ppm) increases the tension between experiment and theory to 4.2 standard deviationsComment: 10 pages; 4 figure

    The measurement of the anomalous magnetic moment of the muon at fermilab

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    The anomalous magnetic moment of the muon is one of the most precisely measured quantities in experimental particle physics. Its latest measurement at Brookhaven National Laboratory deviates from the Standard Model expectation by approximately 3.5 standard deviations. The goal of the new experiment, E989, now under construction at Fermilab, is a fourfold improvement in precision. Here, we discuss the details of the future measurement and its current status

    Detailed Report on the Measurement of the Positive Muon Anomalous Magnetic Moment to 0.20 ppm

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    We present details on a new measurement of the muon magnetic anomaly, aÎŒ=(gΌ−2)/2a_\mu = (g_\mu -2)/2. The result is based on positive muon data taken at Fermilab's Muon Campus during the 2019 and 2020 accelerator runs. The measurement uses 3.13.1 GeV/c/c polarized muons stored in a 7.17.1-m-radius storage ring with a 1.451.45 T uniform magnetic field. The value of aÎŒ a_{\mu} 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 aÎŒ=116592057(25)×10−11a_\mu = 116 592 057 (25) \times 10^{-11} (0.21 ppm). This is the world's most precise measurement of this quantity and represents a factor of 2.22.2 improvement over our previous result based on the 2018 dataset. In combination, the two datasets yield aÎŒ(FNAL)=116592055(24)×10−11a_\mu(\text{FNAL}) = 116 592 055 (24) \times 10^{-11} (0.20 ppm). Combining this with the measurements from Brookhaven National Laboratory for both positive and negative muons, the new world average is aÎŒa_\mu(exp) =116592059(22)×10−11 = 116 592 059 (22) \times 10^{-11} (0.19 ppm)
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