Muon g-2: Taking Particle Physics for a Spin

Synopsis

The muon—a heavier cousin of the electron—plays a unique role in particle physics, offering powerful ways to search for new physics beyond the Standard Model. Over the past few decades, precision measurements involving muons have deepened our understanding of fundamental particle interactions. One of the most prominent efforts is the Muon g-2 Experiment at Fermilab, which was designed to measure the muon's magnetic anomaly, aμ = (gμ – 2)/2, with an unprecedented precision of 140 parts per billion—four times more precise than the earlier measurement at Brookhaven National Laboratory (BNL). The new experiment was motivated since the BNL result had revealed a tantalizing discrepancy of about 3.5 standard deviations from the Standard Model prediction. The Muon g-2 collaboration has recently completed its full data analysis, achieving a final precision of 127 parts per billion. This new result sets the most stringent benchmark to date for testing extensions to the Standard Model. In this colloquium, I will give a broad overview of the muon’s role in particle physics, followed by a focused discussion of the Fermilab Muon g-2 experiment and its implications.