Study on manipulation mechanism of polarized positrons in nonlinear Breit-Wheeler scattering process

Polarized positron beams are vital probes in fundamental physics. Generating them via the nonlinear Breit-Wheeler process in laser fields is a promising new approach, but control over the positron polarization requires further understanding.

This study investigates how laser and γ-photon parameters control the final polarization of positrons in this process.

Within strong-field QED, we fully include all particle spins and the laser pulse’s finite envelope. Systematic calculations are performed for various laser intensities, γ-photon energies, and polarization configurations.

Key findings are: (1) No positron polarization arises with linearly polarized lasers and γ-photons. (2) When only one is circularly polarized, it dominates the positron polarization, which decreases with higher laser intensity or γ-photon energy. (3) When both are circularly polarized, γ-photons dominate high-energy positron polarization, while both sources co-determine low-energy positron polarization, with laser intensity playing a stronger regulatory role.

These results clarify the dominant factors for positron polarization, providing a key theoretical basis for designing optimized laser-driven polarized positron sources.