  The E821 experiment at Brookhaven National Laboratory is designed to measure
the muon magnetic anomaly, a_mu, to an ultimate precision of 0.4 parts per
million (ppm). Because theory can predict a_mu to 0.6 ppm, and ongoing efforts
aim to reduce this uncertainty, the comparison represents an important and
sensitive test of new physics. At the time of this Workshop, the reported
experimental result from the 1999 running period achieved a_mu = 11 659
202(14)(6)x 10^-10 (1.3 ppm) and differed from the most precise theory
evaluation by 2.6 standard deviations. Considerable additional data has already
been obtained in 2000 and 2001 and the analysis of this data is proceeding
well. Intense theoretical activity has also taken place ranging from
suggestions of the new physics which could account for the deviation to careful
re-examination of the standard model contributions themselves. Recently, a
re-evaluation of the pion pole contribution to the hadronic light-by-light
process exposed a sign error in earlier studies used in the standard theory.
With this correction incorporated, experiment and theory disagree by a modest
1.6 standard deviations.
