Detecting Nonlinear Breit-Wheeler Pairs at CALA

One of the most intriguing physics processes that remain untested is the single-step electron-positron pair production via quantum-vacuum fluctuations described by the nonlinear Breit-Wheeler process. The virtual pairs from the vacuum fluctuations can be turned into real particles by applying electric fields above the Schwinger limit of 1.3 x 10¹⁸ V/m. Despite the advent of high-intensity lasers, the critical limit is still far beyond the technologically achievable, however, such fields can be reached in the rest frame of the created pairs after the collision of high-energy γ-ray photons with the highly intense laser beam.

We describe the experiment designed by the FOR2783 research collaboration [1] to probe the single-step pair-creation process for the first time at the ATLAS laser at CALA. In the experiment, a high-energy bremsstrahlung γ-ray, produced using a 2.5 GeV monoenergetic electron beam with a charge of 10 pC, collides with a laser beam of intensity 9.5 x 10²¹ W/cm² (a0 = 66), triggering the pair creation process.

The created pairs are detected by a single-particle detection system composed of LYSO:Ce tracking layers and a Cherenkov calorimeter. GEANT4 Monte-Carlo simulations of the full experiment and expected pair yields are presented.

[1] http://quantumvacuum.org/