The Muon Anomaly: Experiment and Theory

TL;DR

This paper reviews the current experimental and theoretical status of the muon's anomalous magnetic moment, highlighting a small but significant discrepancy that may suggest new physics beyond the Standard Model.

Contribution

It provides an updated summary of experimental measurements and theoretical calculations, including recent corrections that impact the muon g-2 discrepancy.

Findings

Recent experimental value differs from Standard Model prediction by about 1.6 standard deviations.

A correction in the hadronic light-by-light contribution reduces the discrepancy.

Ongoing data analysis aims to clarify the potential for new physics evidence.

Abstract

A summary is given of the present status of the theory and experiment of the anomalous magnetic moment of the muon. A difference between predicted and measured values is an indication of physics beyond the Standard Model. A new experimental number has produced a value which differs from a recent Standard Model prediction by about 1.6 standard deviations. When the new result was first announced, the discrepancy was about 2.6 standard deviations, but theorists have recently found an error in the sign of the largest term in the Standard Model hadronic light-by-light contribution which reduces the difference. Additional data are being analyzed and elements of the theory are being scrutinized to provide, in the future, a sharper test of theory.