Breit–Wheeler process

This is also the case for the multi-photon Breit–Wheeler, which was observed at the Stanford Linear Accelerator Center in 1997 by colliding high-energy electrons with a counter-propagating terawatt laser pulse.

[6][7] Although this mechanism is still one of the most difficult to be observed experimentally on Earth, it is of considerable importance for the absorption of high-energy photons travelling cosmic distances.

In 1928, Paul Dirac's work proposed that electrons could have positive and negative energy states following the framework of relativistic quantum theory but did not explicitly predict the existence of a new particle.

Although the process is one of the manifestations of the mass–energy equivalence, as of 2017, the pure Breit–Wheeler has never been observed in practice because of the difficulty in preparing colliding gamma ray beams and the very weak probability of this mechanism.

They would then fire these electrons into a slab of gold to create a beam of photons a billion times more energetic than those of visible light.

[10] Monte Carlo simulations suggest that this technique is capable of producing of the order of 105 Breit–Wheeler pairs in a single shot.

[11][12] In 2016, a second novel experimental setup was proposed theoretically[4] to demonstrate and study the Breit–Wheeler process by colliding two high-energy photon sources (composed of non-coherent hard x-ray and gamma-ray photons) generated from the interaction of two extremely intense lasers on solid thin foils or gas jets.

To first create the photons and then have the pair production in an all-in-one setup, the similar configuration can be used by colliding GeV electrons.

The resulting electron bunch is then made to interact with a second high-power laser in order to study QED processes.

In July 2021 evidence consistent with the process was reported by the STAR detector one of the four experiments at the Relativistic Heavy Ion Collider although it was unclear if it was due to massless photons or massive virtual photons, vacuum birefringence was also studied obtaining evidence enough to claim the first known observation of the process.