Scaling laws for positron production in laser–electron-beam collisions

Abstract

Showers of γ-rays and positrons are produced when a high-energy electron beam collides with a super-intense laser pulse. We present scaling laws for the electron beam energy loss, the γ-ray spectrum, and the positron yield and energy that are valid in the non-linear, radiation-reactiondominated regime. As an application we demonstrate that by employing the collision of a >GeV electron beam with a laser pulse of intensity > 5 × 10 21 Wcm −2 , today's high-intensity laser facilities are capable of producing O(10 4 ) positrons per shot via light-by-light scattering.

Nonlinear Breit–Wheeler pair creation with bremsstrahlungγrays

“…Reaching χ γ ∼1 with the intensities that may be reached with today's high-intensity lasers~-( ) 10 W cm 21 2 , requires photon energies in the GeV range [20]. We now turn to how bremsstrahlung of an ultrarelativistic electron beam in a high-Z material may be used as the source of such photons.…”

“…Integrating the probability rate for pair creation from [25] over the trajectory specified by (2), using the same saddlepoints method as [20], we find that the pair creation probability…”

“…where α is the fine-structure constant, n eff is as given in (3) and as in [20]. The argument of  in (4) is the peak χ γ of the photon.…”

“…To verify this, we use GEANT4 to simulate the interaction of an electron beam with a solid target, then take the resultant photon spectrum as input to CIRCE [20,36], a single-particle Monte Carlo code that simulates strong-field QED cascades in intense laser pulses. It does this by factorizing the cascade into a product of first-order processes (nonlinear Compton scattering and Breit-Wheeler pair creation), which occur along the particle trajectory at locations pseudorandomly determined according to the appropriate LCFA probability rate.…”

“…Using bremsstrahlung to produce the seed photons, rather than Compton scattering in a direct collision between electron beam and laser pulse [20], is motivated by the breadth of the energy spectrum [21]. As it extends up to the initial energy of the electron, using GeV electron beams will produce the GeV photons that are necessary for χ γ  0.1.…”