Bright $\gamma$ rays source and copious nonlinear Breit-Wheeler pairs in the collision of high density particle beams

Abstract

The collision of ultrashort high-density $e^{-}$ or $e^{-}$ and $e^{+}$ beams at 10s of GeV, to be available at the FACET II and in laser wakefield accelerator experiments, can produce highly collimated $\gamma$ rays (few GeVs) with peak brilliance of $10^{27}ph/s\mathrm{m}{\mathrm{m}}^2\mathrm{mra}{\mathrm{d}}^{2}0.1\%BW$ and up to $10^5$ nonlinear Breit-Wheeler pairs. We provide analytical estimates of the photon source properties and of the yield of secondary pairs, finding excellent agreement with full-scale 3D self-consistent particle-in-cell simulations that include quantum electrodynamics effects. Our results show that beam-beam collisions can be exploited as secondary sources of $\gamma$ rays and provide an alternative to beam-laser setups to probe quantum electrodynamics effects at the Schwinger limit.