Muon g-2 — LLMpedia

Muon g-2
Reidar Hahn · CC BY-SA 4.0 · source
Name	Muon g-2
Discovered	1940s–2020s
Field	Particle physics
Notable	Brookhaven National Laboratory, Fermi National Accelerator Laboratory, CERN, Paul Scherrer Institut

Contents

Muon g-2

The muon g-2 anomaly refers to precision measurements of the anomalous magnetic moment of the muon performed by collaborations at Brookhaven National Laboratory, Fermi National Accelerator Laboratory, CERN, Paul Scherrer Institut, and associated universities. Results have driven interplay among experimental teams such as the Muon g-2 Experiment (FNAL), theoretical groups at Princeton University, Massachusetts Institute of Technology, Institute for Advanced Study, and lattice collaborations including Fermilab Lattice and RBC and UKQCD. The topic connects to historical studies at Columbia University, University of Chicago, Harvard University, and foundational theory by figures associated with Paul Dirac and Julian Schwinger.

Background and theoretical context

Early theoretical work by Paul Dirac predicted a gyromagnetic ratio g = 2 for spin-1/2 particles, while radiative corrections computed by Julian Schwinger introduced the first-order quantum electrodynamics contribution. Subsequent developments involved calculations by groups at Institute for Advanced Study, Stanford University, Yale University, and Cornell University extending perturbative expansions in Richard Feynman diagram techniques and renormalization methods pioneered by Sin-Itiro Tomonaga, Shin'ichirō Tomonaga, Freeman Dyson, and Gerard 't Hooft. Theoretical contributions require inputs from hadronic physics institutions such as CERN, DESY, SLAC National Accelerator Laboratory, KEK, Max Planck Institute for Physics, and collaborations like Particle Data Group and Muon g-2 Theory Initiative to combine quantum electrodynamics, electroweak, and hadronic vacuum polarization corrections.

Precision experiments have been carried out at historical facilities including Brookhaven National Laboratory and contemporary runs at Fermi National Accelerator Laboratory using detectors and storage rings engineered by teams from University of Washington, University of Minnesota, Rutgers University, University of Tokyo, University of Pennsylvania, University of Chicago, University of British Columbia, and University of Victoria. Earlier magnetic moment work traces to apparatuses at University of Cambridge and University of Oxford and techniques developed for LEP studies at CERN. Measurements rely on infrastructure and oversight from agencies such as US Department of Energy, National Science Foundation, European Research Council, and laboratory partners including Argonne National Laboratory and Lawrence Berkeley National Laboratory.

The Standard Model prediction aggregates calculations from quantum electrodynamics contributions by researchers at MIT, Princeton University, Caltech, and University of Illinois Urbana-Champaign; electroweak loops studied by groups at Fermi National Accelerator Laboratory and Brookhaven National Laboratory; and hadronic effects constrained by data from experiments at BaBar, Belle, KLOE, CMD-3, SND, VEPP-2000, BESIII, and facilities like SLAC. Lattice QCD results originate from collaborations such as Fermilab Lattice, RBC and UKQCD, ETM Collaboration, BMW Collaboration, and institutes including RIKEN, CERN Theory Division, National Institute for Nuclear Physics (INFN), and Johannes Gutenberg University Mainz. Global theory coordination involves the Muon g-2 Theory Initiative, the Particle Data Group, and workshops at Perimeter Institute.

Reported deviations between measurement and Standard Model expectation prompted interest from model builders at Harvard University, Princeton University, University of California, Berkeley, University of Cambridge, Imperial College London, University of Oxford, University of Chicago, and Columbia University. Proposed explanations include contributions from supersymmetric particles considered by researchers associated with CERN, SLAC, DESY, and theorists such as those collaborating with Niels Bohr Institute, Kavli Institute for Theoretical Physics, Max Planck Institute for Physics, and Institute for Advanced Study. Other frameworks explored by groups at Rutgers University, University of Michigan, University of Tokyo, Kyoto University, Seoul National University, University of Toronto, and McGill University involve dark photons, leptoquarks, and extended Higgs sectors analyzed in contexts of Large Hadron Collider searches at ATLAS and CMS and intensity-frontier experiments coordinated with J-PARC and DUNE. Phenomenological implications have been debated in conferences at CERN, KEK, TRIUMF, Brookhaven National Laboratory, and Fermilab.

Techniques utilize storage rings, magnetic field mapping, and beam dynamics developed with contributions from Brookhaven National Laboratory, Fermilab, CERN, Paul Scherrer Institut, Lawrence Livermore National Laboratory, and university groups at University of Michigan, Northwestern University, University of California, Santa Barbara, and Texas A&M University. Systematics analyses draw on expertise from Particle Data Group, National Institute of Standards and Technology, Los Alamos National Laboratory, Argonne National Laboratory, National Taiwan University, and collaborations with Oak Ridge National Laboratory. Key uncertainties arise in magnetic field calibration, detector gain stability, and muon beam polarization control—areas studied in joint programs with DESY, SLAC, KEK, J-PARC, and instrumentation groups at CERN.

Ongoing work continues at Fermi National Accelerator Laboratory with participation from institutions including University of Kentucky, University of Virginia, University of Liverpool, INFN, Università di Pisa, University of Bonn, Universität Mainz, Ludwig Maximilian University of Munich, Niels Bohr Institute, CERN, and Paul Scherrer Institut. Future plans consider complementary measurements at J-PARC, proposed campaigns at CERN, refined lattice computations by Fermilab Lattice, BMW Collaboration, and RBC and UKQCD, and cross-checks via experiments at BESIII, Belle II, VEPP-2000, and intensity-frontier projects like DUNE and SHiP. Global coordination involves funding agencies such as US Department of Energy, National Science Foundation, European Research Council, Japan Society for the Promotion of Science, and scientific program offices at CERN and Fermilab to resolve the anomaly with greater precision.