Photon–photon Breit–Wheeler possible experimental configurations 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. Recently, different teams have proposed novel theoretical studies on possible experimental configurations to finally observe it on Earth. In 2014, physicists at
Imperial College London proposed a relatively simple way to physically demonstrate the Breit–Wheeler process.
Monte Carlo simulations suggest that this technique is capable of producing of the order of 105 Breit–Wheeler pairs in a single shot. In 2016, a second novel experimental setup was proposed theoretically which then underwent multiple collisions to produce electrons and positrons, all within the same chamber. Electrons were accelerated in the linear accelerator to an energy of 46.6 GeV before being sent head-on into a
Neodymium (Nd:glass)
linear polarized laser of intensity 1018 W/cm2 (maximal
electric field amplitude of around 6×109 V/m), of
wavelength 527 nanometers and duration 1.6 picoseconds. In this configuration, it has been estimated that photons of energy up to 29 GeV were generated. This led to the yield of 106 ±14 positrons with a broad energy spectrum in the GeV level (peak around 13 GeV). The aforementioned experiment may be reproduced in the future at
SLAC with more powerful laser technologies. The use of higher laser intensities (1020 W/cm2) is now easily achievable with short-pulse
titanium-sapphire laser solutions that would significantly enhance process efficiencies (inverse nonlinear Compton and nonlinear Breit–Wheeler pair creation) leading to several orders of magnitude higher antimatter production, enabling higher-resolution measurements, additional mass-shift, as well as nonlinear and spin effects. The extreme intensities expected to be available in future multi-petawatt laser systems will allow all-optical, laser–electron collision experiments where the electron beam is generated from direct laser interaction with a gas jet in a so-called
laser wakefield acceleration regime. The resulting electron bunch is then made to interact with a second high-power laser in order to study QED processes. The feasibility of an all-optical multi-photon Breit–Wheeler pair production scheme has first been proposed theoretically in Implementation of this scheme is restricted to multi-beam short-pulse extreme-intensity laser facilities such as the CILEX-Apollon and
ELI systems (CPA titanium sapphire technology at 0.8 micrometer, duration of 15–30 femtoseconds). The generation of electron beams of few GeV and few nanocoulomb is possible with a first laser of 1 petawatt combined with the use of tuned and optimized gas-jet density profiles such as two-step profiles. Strong pair generation can be achieved by colliding head-on this electron beam with a second laser of intensity above 1022 W/cm2. In this configuration at this level of intensity, theoretical studies predict that several hundreds of pico-Coulombs of antimatter could be produced. This experimental setup could even be one of the most prolific positron yield factory. This all-optical scenario may be preliminary tested with lower laser intensities of the order of 1021 W/cm2. 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. ==See also==