For decades, electron scattering has been a key tool in the study of nuclear physics. In these experiments, electron beams are often incident on stationary atomic targets. Here, a beam electron can collide with either a nucleus or an atomic electron, meaning that the electron-electron interaction must be quantified as well to serve as a baseline. Calculations for this have existed since the 1960s, but a new wave of high-precision, low-energy experiments have exposed gaps in our understanding, particularly the treatment of radiative effects and the electron mass. We have updated the calculations and have designed, constructed and implemented a new experiment to test them directly for the first time.
