Muon g-2: Anomalous Magnetic Moment in a Storage Ring

A muon circulating in a magnetic storage ring carries two rotating arrows: its momentum, which turns at the cyclotron frequency ω_c = qB/(γm), and its spin, which precesses according to the Thomas–BMT equation at a rate set by the particle's g-factor. If g were exactly 2, as Dirac's equation predicts for a point particle, the two arrows would rotate in lockstep forever. Quantum electrodynamics says otherwise — virtual photon loops nudge g very slightly above 2, and the tiny anomaly a = (g−2)/2 makes the spin slowly outpace the momentum, lap after lap. This simulator renders that storage ring in 3D, lets you dial the magnetic field, the anomaly a, and a visual amplification factor (since the real drift is far too small to see directly), and reads out the cyclotron, spin and anomalous precession frequencies live alongside a "wiggle plot" of the spin-momentum angle — the same signal real g-2 experiments at Fermilab and CERN use to test QED to ten decimal places.