# The History of the Muon (g-2) Experiments

### Submission summary

 As Contributors: B. Lee Roberts Arxiv Link: https://arxiv.org/abs/1811.06974v1 (pdf) Date accepted: 2019-01-10 Date submitted: 2018-11-19 Submitted by: Roberts, B. Lee Submitted to: SciPost Physics Proceedings Proceedings issue: The 15th International Workshop on Tau Lepton Physics (Amsterdam, 2018-09) Discipline: Physics Subject area: Quantum Physics Approach: Experimental

### Abstract

I discuss the history of the muon $(g-2)$ measurements, beginning with the Columbia-Nevis measurement that observed parity violation in muon decay, and also measured the muon $g$-factor for the first time, finding $g_\mu=2$. The theoretical (Standard Model) value contains contributions from quantum electrodynamics, the strong interaction through hadronic vacuum polarization and hadronic light-by-light loops, as well as the electroweak contributions from the $W$, $Z$ and Higgs bosons. The subsequent experiments, first at Nevis and then with increasing precision at CERN, measured the muon anomaly $a_\mu = (g_\mu-2)/2$ down to a precision of 7.3 parts per million (ppm) The Brookhaven National Laboratory experiment E821 increased the precision to 0.54 ppm, and observed for the first time the electroweak contributions. Interestingly, the value of $a_\mu$ measured at Brookhaven appears to be larger than the Standard Model value by greater than three standard deviations. A new experiment, Fermilab E989, aims to improve on the precision by a factor of four, to clarify whether this result is a harbinger of new physics entering through loops, or from some experimental, statistical or systematic issue.

Published as SciPost Phys. Proc. 1, 032 (2019)

### Submission & Refereeing History

Submission 1811.06974v1 on 19 November 2018

## Reports on this Submission

### Report

This contribution is a clear and historic overview of the various experiments devoted to the measurement of the muon anomalous magnetic moment, highlighting the key features of the various experimental setups that led to the current precision. I recommend these proceedings for publication.

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