Observing the two-photon Breit-Wheeler process for the first time*

As the inverse of Dirac annihilation, the Breit-Wheeler process [1], the production of an electron-positron pair in the collision of two photons, is the simplest mechanism by which light can be transformed into matter. It is also of fundamental importance in high-energy astrophysics, both in the context of the dense radiation fields of compact objects [2] and the absorption of high-energy gamma rays travelling intergalactic distances [3]. However, in the 80 years since its theoretical prediction, this process has never been observed. Here, we present the design of a new class of photon-photon collider [4], which is capable of detecting significant numbers of Breit-Wheeler pairs using current-generation technology. We further show how our scheme could be implemented on existing laser facilities; successfully achieving this would represent the advent of a new type of high-energy physics experiment. \\[4pt] [1] G. Breit and J.A. Wheeler, \textit{Phys.~Rev.} \textbf{46,} 1087 (1934)\\[0pt] [2] S. Bonometto and M.J. Rees, \textit{MNRAS} \textbf{152,} 21 (1971)\\[0pt] [3] R.J. Gould and G. Schr\'eder, \textit{Phys.~Rev.~Lett.} \textbf{16,} 252 (1966)\\[0pt] [4] O.J. Pike \textit{et al}, \textit{Nature~Photon.} \textbf{8,} 434 (2014)