Final Report of the Muon E821 Anomalous Magnetic Moment Measurement at BNL

TL;DR

This paper reports a highly precise measurement of the muon anomalous magnetic moment, a_mu, at Brookhaven, which shows a significant deviation from the Standard Model prediction, indicating potential new physics.

Contribution

It provides the most accurate experimental value of a_mu to date, with a 14-fold improvement over previous measurements, and compares it with theoretical calculations highlighting discrepancies.

Findings

Experimental a_mu value: 11 659 208.0(5.4)(3.3) x 10^-10

Deviation from Standard Model: 2.2 - 2.7 standard deviations

Uncertainty reduction: 14-fold improvement over prior measurements

Abstract

We present the final report from a series of precision measurements of the muon anomalous magnetic moment, a_mu = (g-2)/2. The details of the experimental method, apparatus, data taking, and analysis are summarized. Data obtained at Brookhaven National Laboratory, using nearly equal samples of positive and negative muons, were used to deduce a_mu(Expt) = 11 659 208.0(5.4)(3.3) x 10^-10, where the statistical and systematic uncertainties are given, respectively. The combined uncertainty of 0.54 ppm represents a 14-fold improvement compared to previous measurements at CERN. The standard model value for a_mu includes contributions from virtual QED, weak, and hadronic processes. While the QED processes account for most of the anomaly, the largest theoretical uncertainty, ~0.55 ppm, is associated with first-order hadronic vacuum polarization. Present standard model evaluations, based on e+e- hadronic cross sections, lie 2.2 - 2.7 standard deviations below the experimental result.