The muon is a short-lived cousin of the electron that’s about 200 times heavier, and a landmark Fermilab experiment has measured its tiny “magnet strength” with extreme precision; to check whether our best physics theory still holds up, scientists now need equally precise calculations of how the muon’s interaction with the strong force affects that magnetism, using powerful supercomputer simulations.
The muon is an elementary particle identical to the ordinary electron except that it is about 200 times heavier. Its magnetic dipole moment has been measured at Fermilab in an historic experiment (E989) to a precision of 1.27 parts-per-million. To test the limit of our current understanding of Nature’s laws (aka, the standard model of particle physics) and fully leverage the DOE’s investment in E989, the dominant theory errors arising from the contributions to the magnetic moment from the cloud of virtual quarks, anti-quarks, and gluons surrounding the muon during its brief lifetime must be reduced to this same level of precision. To reach this goal, these so-called hadronic contributions will be determined using numerical simulations of Quantum Chromodynamics (QCD) known as lattice QCD. QCD encapsulates the so-called strong force, one of the four fundamental forces of Nature comprising the standard model.