Measurement of the Positive Muon Anomalous Magnetic Moment to 0.46 ppm


B. Abi, University of Oxford
T. Albahri, University of Liverpool
S. Al-Kilani, University College London
D. Allspach, Fermi National Accelerator Laboratory
L. P. Alonzi, University of Washington
A. Anastasi, Istituto Nazionale di Fisica Nucleare, Sezione di Pisa
A. Anisenkov, Budker Institute of Nuclear Physics of the Siberian Branch of the RAS
F. Azfar, University of Oxford
K. Badgley, Fermi National Accelerator Laboratory
S. Baeßler, University of Virginia
I. Bailey, Lancaster University
V. A. Baranov, Joint Institute for Nuclear Research, Dubna
E. Barlas-Yucel, University of Illinois Urbana-Champaign
T. Barrett, Cornell University
E. Barzi, Fermi National Accelerator Laboratory
A. Basti, Istituto Nazionale di Fisica Nucleare, Sezione di Pisa
F. Bedeschi, Istituto Nazionale di Fisica Nucleare, Sezione di Pisa
A. Behnke, Northern Illinois University
M. Berz, Michigan State University
M. Bhattacharya, University of Mississippi
H. P. Binney, University of Washington
R. Bjorkquist, Cornell University
P. Bloom, North Central College
J. Bono, Fermi National Accelerator Laboratory
E. Bottalico, Istituto Nazionale di Fisica Nucleare, Sezione di Pisa
T. Bowcock, University of Liverpool
D. Boyden, Northern Illinois University
G. Cantatore, Istituto Nazionale di Fisica Nucleare, Sezione di Trieste
R. M. Carey, Boston University
J. Carroll, University of Liverpool
B. C.K. Casey, Fermi National Accelerator Laboratory
D. Cauz, Istituto Nazionale di Fisica Nucleare - INFN
S. Ceravolo, INFN, Laboratori Nazionali Di Frascati
R. Chakraborty, University of Kentucky

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We present the first results of the Fermilab National Accelerator Laboratory (FNAL) Muon g-2 Experiment for the positive muon magnetic anomaly aμ(gμ-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 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 p ′ in a spherical water sample at 34.7 °C. The ratio ωa/ω p ′, together with known fundamental constants, determines aμ(FNAL)=116 592 040(54)×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 μ+ and μ-, the new experimental average of aμ(Exp)=116 592 061(41)×10-11 (0.35 ppm) increases the tension between experiment and theory to 4.2 standard deviations.

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