The Muon g – 2 Experiment

Introduction As its overarching quest, particle physics seeks to discover the complete set of fundamental components of matter and understand the forces through which they interact. Progress in our understanding, eventually culminating the Standard Model (SM) of fundamental particles, has been driven by increasing the energy available in the Center of Mass of collisions, the Energy Frontier, or through highprecision experiments that typically require large statistics, the Intensity Frontier. While the SM explains an astonishing range of phenomena, fundamental questions remain unanswered by the model: why three generations of quarks and of leptons; does the Higgs sector really provide the mass generation mechanism for quarks and leptons; what keeps the Higgs boson mass small when radiative corrections should drive it large; and many others. Explorations in both particle and nuclear physics at both frontiers strive to address these questions. The Intensity Frontier itself encompasses two complementary strategies: the search for rare or forbidden processes, like Lepton Flavor Violating (LFV) decays, that have highly suppressed rates within the SM but can receive significant rate enhancements in extensions of the SM, or the high-precision measurement of a fundamental quantity in which to search for a discrepancy with the value predicted by the SM. A discrepancy between measurement and prediction can hint at new physics, while agreement can often provide limits on the mass scales of new physics in various models well beyond those directly accessible at the energy frontier. This article addresses an example of the second method, the high-precision measurement of the muon magnetic anomaly, often known as g – 2, which has a long and rich history of theoretical and experimental successes that contributed to the establishment of the SM.