Testing quantum electrodynamics prediction with surprising results

Echoing classical physics, quantum electrodynamics predicts the release of a spectral continuum of electromagnetic radiation upon the sudden acceleration of charged particles in quantum matter. Despite apparent theoretical success in describing sister nuclear processes, known as internal bremsstrahlung, following nuclear beta decay and K capture, the situation of the photoejection of an electron from an inner shell of an atom, intraatomic bremsstrahlung (IAB), is far from settled.

What is the discovery?
This paper addresses the experimental situation by applying a fluorescence coincidence technique to pluck the anticipated signal out of noise, taking advantage of the intense incident photon flux of a contemporary synchrotron radiation source; exploits advanced x-ray detectors which provide arrival time as well as energy information, and employs extraordinarily thin metal targets to minimize secondary effects. The surprising result is that in testing for the radiation expected from the innermost shell of copper with a 46 keV incident x-ray beam no such signal was observed at a sensitivity level that is over five sigmas below the predicted rate, taking into account the expected secondary signal, and below four sigmas if no particular secondary modeling is assumed.  In this work observations were made in the scattered photon energy range of 3 to 7 keV.

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Image: Schematic of the Scattering Chamber. A is the one element detector, B is the Kapton film covered main beam exit port, C is the helium (1 Atm.) filled chamber (input and output helium supply lines and chamber cover not shown), D is the target mount, E is the four-element detector, F is the Kapton film covered incident beam port.