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Beam dynamics corrections to the Run-1 measurement of the muon anomalous magnetic moment at Fermilab

T. Albahri et al. (Muon g2 Collaboration)
Phys. Rev. Accel. Beams 24, 044002 – Published 27 April 2021
Physics logo See Viewpoint: Muon’s Escalating Challenge to the Standard Model

Abstract

This paper presents the beam dynamics systematic corrections and their uncertainties for the Run-1 dataset of the Fermilab Muon g2 Experiment. Two corrections to the measured muon precession frequency ωam 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 ωam is 0.50±0.09ppm; the uncertainty is small compared to the 0.43 ppm statistical precision of ωam.

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  • Received 11 March 2021
  • Accepted 1 April 2021

DOI:https://doi.org/10.1103/PhysRevAccelBeams.24.044002

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

  1. Research Areas
  1. Properties
Accelerators & Beams

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Muon’s Escalating Challenge to the Standard Model

Published 7 April 2021

Measurements of the muon magnetic moment strengthen a previously reported tension with theoretical predictions, ushering in a new era of precision tests of the standard model.

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See Also

Measurement of the Positive Muon Anomalous Magnetic Moment to 0.46 ppm

B. Abi et al. (Muon g2 Collaboration)
Phys. Rev. Lett. 126, 141801 (2021)

Measurement of the anomalous precession frequency of the muon in the Fermilab Muon g2 Experiment

T. Albahri et al. (Muon g2 Collaboration)
Phys. Rev. D 103, 072002 (2021)

Magnetic-field measurement and analysis for the Muon g2 Experiment at Fermilab

T. Albahri et al. (The Muon g2 Collaboration)
Phys. Rev. A 103, 042208 (2021)

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Vol. 24, Iss. 4 — April 2021

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