Towards the observation of linear Breit-Wheeler process in ultra-intense laser-plasma experiments

Linear Breit-Wheeler (BW) process (γγ→e⁺e^-) is one of the fundamental processes in the theory of quantum electrodynamics, but yet to be observed in experiments. Previous research [Comm. Phys. 4, 139 (2021)] has shown that a significant number (>10⁸) of linear BW pairs can be generated by colliding two ultra-intense laser pulses (at intensities of 2×10²² W/cm²) inside a plasma channel. Simulations with our newly implemented module demonstrate that these positrons can be accelerated to GeV energies by the remaining laser pulses and form collimated energetic linear BW positron beams. The impact of target parameters on the pair yields by different pair creation mechanisms in the system is also investigated. It is found that the relative contributions to the pair yields by the linear BW, the nonlinear BW, and the Bethe-Heitler processes can be controlled by only changing the target length and channel density within the experimentally controllable regime [Phys. Plasmas 29, 053105 (2022)]. Our result shows that the setup of colliding pulses inside a structured plasma target has the potential to achieve the first observation of the linear BW process using real photons with experimentally available laser pulses and targets.