Feasibility of measuring non-analytic QED coupling from pair creation in strong fields

Abstract: In the quasistatic regimes of nonlinear Breit-Wheeler and trident pair creation, the rates can exhibit a non-analytic dependency on the fundamental coupling of quantum electrodynamics (QED), in a form similar to Schwinger vacuum pair creation. To reach this tunneling regime requires satisfying competing requirements: high intensity but low strong-field parameter with sufficient pair creation to be observed. Using a locally monochromatic approach, we identify the parameter regime where tunneling pair-creation could be measured for the first time in experiment. Studying several scenarios of collisions with focussed Gaussian pulses, including a bremsstrahlung and an inverse Compton source for nonlinear Breit-Wheeler and a Gaussian electron beam for nonlinear trident, we find the position of the tunneling parameter regime to be well-defined and robust.