The BNL Muon Anomalous Magnetic Moment Measurement

TL;DR

The paper discusses the measurement of the muon magnetic anomaly at Brookhaven, comparing experimental results with theoretical predictions, highlighting recent corrections and the potential for new physics insights.

Contribution

It reports the latest experimental measurements of a_mu, updates on theoretical calculations, and addresses recent corrections affecting the comparison between experiment and theory.

Findings

Experimental a_mu = 11 659 202(14)(6) x 10^-10 with 1.3 ppm precision

Discrepancy between experiment and theory reduced from 2.6 to 1.6 standard deviations after correction

Ongoing data collection and theoretical analysis continue to refine the measurement and understanding

Abstract

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.