Design and fabrication of a compact spectrometer to observe positrons in a single laser-driven gamma-ray collider experiment

Generating electron-positron pairs through photon-photon interactions, also known as the linear Breit-Wheeler (BW) process, is one of quantum electrodynamics’ (QED) most challenging processes to experimentally verify. A novel method based on particle-in-cell simulations suggests this process can be driven through a laser-induced gamma-ray collider [1,2]. By shooting a single high-intensity laser, >10²² W/cm², on a specialized target, counter-propagating gamma rays may be generated that collide and produce electron-positron pairs through the BW process. The results suggest ~10⁷ positrons may be accelerated opposite of laser propagation, at energies up to 200MeV. The goal of this research is to experimentally characterize the positron energy spectrum and validate the gamma-ray collider platform. The spectrometer is based on existing systems [3], specifically designed to measure up to 200MeV positrons. Permanent magnets are configured inside a yoke housing to create an ~8kG uniform magnetic field that bends positrons in a circular trajectory. The positrons’ final locations are recorded on a high-sensitivity BAS-MS image plate (IP), which also provides inference to the number of particles. Based on the final locations and IP sensitivity, the energy spectrum of the particle flux can be estimated by cross-referencing with a relativistic kinematic code and calibrated sensitivity data for the IP. Progress on the design and fabrication of this spectrometer will be shown and discussed.