The Quantum Pendulum of the Muon
A spinning top rotates, but its axis remains invisible. That's roughly how a muon behaves — a heavy cousin of the electron. Its spin (intrinsic rotation) changes direction, and the only way to infer this is by how the muon decays. In a new experiment, scientists tracked the spins of about 10 billion muons using data from the Muon g-2 facility at Fermilab.