Generation of Charge-Neutral GeV-Scale Electron-Positron Beams via Bremsstrahlung Gamma Rays from Laser-Wakefield Electrons

Electron-positron pair plasmas, composed of oppositely charged particles with identical mass, exhibit unique collective behaviors and are frequently associated with high-energy astrophysical environments. In laboratory settings, such pairs have traditionally been generated by irradiating high-Z materials with intense laser pulses or laser-driven electron beams. In this study, we demonstrate an alternative approach to produce charge-neutral electron-positron beams extending to GeV energies, utilizing bremsstrahlung gamma rays [1]. Relativistic electron beams exceeding 2 GeV were produced via laser wakefield acceleration using a 4-petawatt (PW) laser at CoReLS, IBS. These electrons, upon interaction with a lead target, emitted bremsstrahlung photons, which in turn generated electron-positron pairs through the Bethe-Heitler process in a secondary lead converter. The resulting pair spectra remained remarkably consistent across the energy range of 10 MeV to 1.8 GeV and showed excellent agreement with Geant4 Monte Carlo simulations. Our results establish a reliable platform for laboratory-based generation of relativistic pair plasmas, providing new opportunities to explore their collective dynamics and fundamental physics.