The Anomalous Magnetic Moment of the Muon

A precise measurement of the anomalous g value, a = (g - 2)/2, for the positive muon has been made at the Brookhaven Alternating Gradient Synchrotron. The result aμ+ = 11 659 202(14)(6) × 10-10 (1.3 ppm) is in good agreement with previous measurements and has an error one third that of the combined previous data. The measurement tests standard theory and has the potential to discover new physics. The analysis of data collected in 2000 and 2001 is well underway and, when combined with data from a requested and final run in the fall of 2002 and winter of 2003, are expected to reduce the experimental uncertainty on aμ to 0.4 ppm.