Breit–Wheeler process

Breit–Wheeler process or Breit–Wheeler pair production is the simplest mechanism by which pure light can be potentially transformed into matter. The process can take the form of γγ′ → e⁺e⁻, that is the emission of positron–electron pairs off a probe photon propagating through a polarized short-pulsed electromagnetic field (for example, laser).

The process was described by Gregory Breit and John A. Wheeler in 1934 in Physical Review. Although the process is one of the manifestations of the mass–energy equivalence, as of 2014, it has never been observed in practice because of the difficulty in preparing colliding gamma ray beams. However, in 1997, researchers at the Stanford Linear Accelerator Centre were able to conduct the so-called multi-photon Breit–Wheeler process using electrons to first create high-energy photons, which then underwent multiple collisions to produce electrons and positrons, all within same chamber.

In 2014, physicists at Imperial College London proposed a relatively simple way to physically demonstrate the Breit–Wheeler process. The collider experiment that the physicists proposed involves two key steps. First, they would use an extremely powerful high-intensity laser to speed up electrons to just below the speed of light. 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. The next stage of the experiment involves a tiny gold can called a hohlraum (German for 'empty room'). Scientists would fire a high-energy laser at the inner surface of this gold can, to create a thermal radiation field. They would then direct the photon beam from the first stage of the experiment through the centre of the can, causing the photons from the two sources to collide and form electrons and positrons. It would then be possible to detect the formation of the electrons and positrons when they exited the can. Monte Carlo simulations suggest that this technique is capable of producing of the order of 10⁵ Breit–Wheeler pairs in a single shot.