A 2001 measurement of the muon magnetic moment at Brookhaven showed a 3.5 standard deviation discrepancy between the measured value and the one predicted by the Standard Model, which has been the talk of the physics world ever since, because the muon magnetic moment (muon g-2) is sensitive to the entire spectrum of particles and forces in a model and this hints at beyond the Standard Model physics.
Fermilab commenced its experiment to repeat the Brookhaven measurement with more precision in November of 2017 following an engineering run in the summer of 2017. It will continue to take most of its data in 2018, with some additional data collection through 2020. When it is complete, the combined experimental error will be approximately a quarter of that of the Brookhaven experiment, in part, because it will collect 21 times as much data. Preliminary results that are still an improvement over the 2001 measurement may be available some time in early 2019.
This new experimental measurement, combined with increased accuracy in the calculation of the Standard Model prediction for muon g-2 which scientists have been working on intensely for the last decade and a half should definitively resolve the question of whether the muon g-2 anomaly is anything more than experimental error, and if so, how large it is, which tells us how close to the Standard Model any new physics must be.