Measurement of the muon anomaly to high and even higher precision

TL;DR

This paper reports a highly precise measurement of the muon anomalous magnetic moment, highlighting its deviation from the standard model and outlining plans for further reducing experimental uncertainty.

Contribution

It presents the most precise measurement to date of the muon g-2 and proposes upgrades to improve accuracy by a factor of 2.5.

Findings

Measured mu to 0.5 ppm precision

Result 2.7 standard deviations above standard model

Plans for a new experiment with 0.2 ppm uncertainty

Abstract

Our recent series of measurements at Brookhaven National Laboratory determined the muon anomalous magnetic moment \amu to a precision of 0.5 ppm. The final result--representing the average of five running periods using both positive and negative muons--is $\amu ^\pm = 11 659 208(6) \times 10^{-10}$. It lies 2.7 standard deviations above the standard model expectation, which is based on updates given at this Workshop. Importantly, only the $e^{+}e^{-}$ annihilation and new KLOE radiative return data are used for the hadronic vacuum polarization input. Because the systematic limit has not been reached in the experiment, a new effort has been proposed and approved with the highest scientific priority at Brookhaven. The goal is an experimental uncertainty of 0.2 ppm, a 2.5-fold reduction in the overall experimental uncertainty. To do so will require a suite of upgrades and several qualitative changes in the philosophy of how the measurement is carried out. I discuss the old and new experiments with a particular emphasis on the technical matters that require change for the future.