Measurement of the Positive Muon Anomalous Magnetic Moment to 0.7 ppm

Abstract

A higher precision measurement of the anomalous g value, aµ = (g − 2)/2, for the positive muon has been made at the Brookhaven Alternating Gradient Synchrotron, based on data collected in the year 2000. The result a µ + = 11 659 204(7)(5) × 10 −10 (0.7 ppm) is in good agreement with previous measurements and has an error about one half that of the combined previous data. The present world average experimental value is aµ(exp) = 11 659 203(8) × 10 −10 (0.7 ppm). The study of magnetic moments has played an important role in our understanding of sub-atomic physics. Precision measurements of the electron anomalous magnetic moment, together with those of the hyperfine structure of hydrogen and the Lamb shift, stimulated the development of modern quantum electrodynamics and have since provided stringent tests of this theory. In this Letter we report a new measurement of the anomalous magnetic moment of the positive muon, a µ = (g − 2)/2, with a relative precision of 0.7 parts per million (ppm), nearly two times better than our previous work [1,2,3]. This measurement comes from data collected in the year 2000. At this level, a µ is sensitive to QED, weak, and hadronic virtual loops and provides an important constraint on extensions to the standard model.The principle of the experiment and previous results have been given in earlier publications [1,2,3]. Also, detailed descriptions of the (g − 2) superconducting inflector magnet, storage ring magnet, fast kicker, NMR system, and calorimeters have been published [4].The quantity a µ is determined fromThe magnetic field B weighted over the muon beam distribution is measured by proton NMR. The difference frequency ω a between the muon spin precession and orbital angular frequencies is determined by counting the number N (t) of decay positrons with energies larger than an energy threshold,The normalization N 0 , asymmetry A, and phase φ a vary with the chosen threshold. The time dilated lifetime is γτ ≈ 64.4 µs. For muons with γ = 29.3, the angular difference frequency ω a is not affected by electrostatic focusing fields in the ring. New aspects of the 2000 data taking period include: the operation of the AGS with 12 beam bunches, contributing to a 4-fold increase in data collected as compared to 1999; a new superconducting inflector magnet, which improved the field homogeneity in the muon storage region; the installation and operation of a sweeper magnet in the beamline, which reduced AGS background; and additional muon loss detectors, which enable an improved determination of the time dependence of muon losses. Most other experimental aspects of the data taking in 2000 were the same as in 1998 and 1999.The magnetic field value was obtained from NMR measurements of the free proton resonance frequency. A trolley with 17 NMR probes was used to measure the field

Beyond Standard Model Collider Phenomenology of Higgs Physics and Supersymmetry

“…It is able to explain the current 3.6σ disagreement between theory and experiment of the muon (g-2) anomalous magnetic moment by introducing new particles in the loops [19][20][21][22][23][24].…”

30th Anniversary Symposium of the US/Japan Collaboration in High Energy Physics

“…3. It took an essential role to obtain the most sensitive muon g-2 value ever achieved [14]. The SSC magnet R&D were performed as eleven 1-m model dipoles and a 13-m long full-scale dipole were constructed and tested successfully.…”

“…The participants had preliminary discussions of an implementing arrangement for the collaboration and agreed as to its general principles. It was also agreed that drafts of an implementing arrangement would be exchanged, with the goal of signing such an agreement 14 soon. It was recommended that a Japan/US Coordinating Committee be established as soon as possible after the signing.…”

“…The second set of meetings of the joint Working Group on Research and Development on New Energy Sources and Related Fields and its Sub-groups was held in Washington on November [14][15][16] 1978 Subtraction imaging by X-ray drug delivery system …”

g-2 of the Muon

“…Therefore the muon magnetic anomaly is a calibration point for our theoretical understanding of the fundamental interactions. Precise measurements can provide limits on potential new interactions or hints to new physics [4][5][6][7].…”