PRL Uncovering Quantum Reflections

Through improved calculations of a quantum phenomenon called Delbrück scattering (Delbrück scattering), German scientists have resolved a long-standing discrepancy between theory and experiment.

The results were published Aug. 8 in Physical Review Letters under the title "All-Order Coulomb Corrections to Delbrück Scattering above the Pair-Production Threshold". .

The color of the sky benefits from a process known as Rayleigh scattering, in which light bounces off electrons bound to atoms. Quantum physics allows for a similar effect known as Delbrück scattering - that is, the reflection of photons in the electrostatic field around the nucleus of an atom. Now Jonas Sommerfeldt and his colleagues at the Technical University of Braunschweig (Germany) have demonstrated high-precision calculations of this "quantum deflection": The results will help analyze nuclear photon scattering experiments and thus increase the understanding of nuclear structure.

According to quantum theory, empty space is not actually empty, but full of particle-antiparticle pairs coming and going. Delbrück scattering occurs when a photon interacts with these particle pairs in the electrostatic field of the nucleus. The probability of this process occurring is represented by a quantity called the "Delbrück cross section". In the case of heavy nuclei, this value from theoretical calculations has been in disagreement with that from experimental data for at least half a century.

Sommerfeldt and his colleagues developed a method for calculating the Delbrück cross section that is accurate for a wide range of photon energies and nuclei.

The key to this innovation is the use of a mathematical function that accounts for the usually neglected contribution to the cross section.

Feynman diagram of Delbrück scattering.

The real (top) and imaginary (bottom) parts of the Delbrück scattering amplitude.

Differential cross section for elastic scattering from a plutonium atom to a 2.754 MeV unpolarized photon. The black dots show previous experimental data, the solid black line indicates theoretical results based on αZ Delbrück full-order calculations, and the shaded area indicates the theoretical error. The red dashed line indicates the theoretical prediction using the lowest-order Born approximation of Delbrück scattering.

As a demonstration, the researchers applied their technique to Delbrück scattering of high-energy photons by plutonium nuclei. Unlike previous calculations, this one yielded cross sections that matched the experimental values, thus resolving the discrepancy described above. The team says that this calculation allows for a sensitive test of quantum electrodynamics, the fundamental theory that describes how light and matter interact.

Reference link:

[1]https://physics.aps.org/articles/v16/s114

[2]https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.131.061601