Rosenbluth scattering and Pauli's approach to anomalous magnetic moments

Abstract

In standard QED, particle interactions are evaluated using minimal coupling coupling the particles solely through their (electric monopole) charges. The Dirac Hamiltonian is used to describe the interaction of a single spin-1/2 particle with an electromagnetic field. Pauli (1934) suggested the addition of a further gauge-invariant term to the Dirac Hamiltonian where the coupling constant for this extra term should not be directly linked to the particle's electric charge. The authors study some of the effects of this additional term and show that for the scattering of electrons off protons, the first-order Pauli-Dirac analysis has at least as good agreement with experiment as previous analyses based on the Dirac Hamiltonian. They show that Rosenbluth used the incorrect sign on the anomalous magnetic moment of the proton. Using Rosenbluth's prescription of considering only the proton's anomalous magnetic moment but correcting the sign, they find only a negligible difference from a completely Dirac analysis. Any proton form factors, and thus any charge distributions, deduced from the Rosenbluth result will be incorrect.