June 16, 2015 15:45 60 Years of CERN Experiments and Discoveries – 9.75in x 6.5in b2114-ch15 page 371 Muon g − 2 and Tests of Relativity FrancisJ.M.Farley∗ Energy and Climate Change Division, Engineering and the Environment, Southampton University, Highfield, Southampton, SO17 1BJ, England, UK
[email protected] After a brief introduction to the muon anomalous moment a ≡ (g − 2)/2, the pioneering measurements at CERN are described. This includes the CERN cyclotron experiment, the first Muon Storage Ring, the invention of the “magic energy”, the second Muon Storage Ring and stringent tests of special relativity. 1. Introduction Creative imagination. That is what science is all about. Not the slow collection of data, followed by a generalisation, as the philosophers like to say. There is as much imagination in science as in art and literature. But it is grounded in reality; the well tested edifice of verified concepts, built up over centuries, brick by brick. All this is well illustrated by the muon (g − 2) theory and measurements at CERN. It also illustrates the reciprocal challenges. Theorists come up with a prediction, for example that light should be bent by gravity: how can you measure it? Eddington found a way. Conversely experiments show that the gyromagnetic ratio of the electron is not 2, but slightly larger: then the theorists are challenged to explain it, and they come up with quantum electrodynamics and a cloud of virtual photons milling around the particle. How can we check this? And so on. By reciprocal challenges the subject advances; step by step.