Properties of pair plasmas emerging from electromagnetic showers in matter

Electromagnetic showers from high-energy electron beams interacting with a target are a promising path to creating pair plasmas in the laboratory. Here, we solve analytically the kinetic equations describing this process. Two regimes are defined by the ratio of the target thickness L to the shower length Lsh, which depends on the electron energy and target composition. For thin targets (L < Lsh), we derive explicit expressions for the spectra of produced photons and pairs, as well as the number of pairs. For thick targets (L > Lsh), we obtain the total pair number and photon spectrum. Analytical results agree well with Geant4 simulations, and it is found that significant pair escape requires L < Lsh. The divergence, density, and characteristic dimensions of the escaping pair jets are derived, and a criterion for pair plasma formation is obtained. While current laser wakefield beams are not well adapted, multi-petawatt lasers may provide new electron or photon sources suitable for laboratory pair plasma production. High-energy electron beams interacting with targets produce electromagnetic showers, a pathway for producing electronpositron pair plasma in the laboratory. Here, the authors solve kinetic equations to derive spectra and pair numbers for varying target thicknesses, with results validated by Geant4 simulations, an explicit formula for the density of outgoing pairs is then obtain.