An electron and a positron can form bound states in just the same way as an electron and a proton. The bound states of e− and e+ are known as positronium states. The spectrum of positronium states is similar to that of hydrogen since the Coulomb force is the same in both cases. The proton in hydrogen can, to a good approximation, be taken to be a fixed center around which the electron orbits. In positronium, however, both partners have the same mass. As always, this two-body problem corresponds mathematically to the motion of a single particle with the reduced mass about a fixed center.
KeywordsAngular Momentum Orbital Angular Momentum Coulomb Force Feynman Rule Principal Quantum Number
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