The muon magnetic moment anomaly, approximately 1.166e-3, arises due to quantum electrodynamics (QED) as well as contributions from weak-interaction and hadronic effects. Because of the muon's mass, the non-QED contributions are significant compared to those for the electron and therefore, the anomaly provides sensitivity to new physics beyond the Standard Model. Precision measurement of the anomaly at Brookhaven (E-821) provided a 0.54 part-per-million (ppm) uncertainty comparable to the Standard-Model theory uncertainty and the difference of experiment and theory for the anomaly is (2.55±0.8)e-9, a discrepancy of more than 3-sigma. A new measurement at Fermilab (E-989) is planned that will improve the uncertainty by a factor of nearly 4 with 20-times higher statistics and a factor of three reduction of systematic errors. The experiment measures the anomaly frequency, which is the precession of the muon magnetic moment with respect to the momentum of muons stored in a 14 m diameter magnetic ring with electrostatic focusing. The magnitude of the magnetic field is determined by a set of proton-NMR measurements in space and time with traceable calibration to a comparison of the proton and electron moments. In this talk I will describe the experiment and plans with particular emphasis on the challenges of our Michigan group's job: determining the magnetic field.

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