Nonlinear Breit–Wheeler pair creation with bremsstrahlung γ rays

T G Blackburn,M Marklund

doi:10.1088/1361-6587/aab3b4

T G Blackburn, M Marklund

Open Access

https://doi.org/10.1088/1361-6587/aab3b4

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Abstract

Electron–positron pairs are produced through the Breit–Wheeler process when energetic photons traverse electromagnetic fields of sufficient strength. Here we consider a possible experimental geometry for observation of pair creation in the highly nonlinear regime, in which bremsstrahlung of an ultrarelativistic electron beam in a high-Z target is used to produce γ rays that collide with a counter-propagating laser pulse. We show how the target thickness may be chosen to optimize the yield of Breit–Wheeler positrons, and verify our analytical predictions with simulations of the cascade in the material and in the laser pulse. The electron beam energy and laser intensity required are well within the capability of today’s high-intensity laser facilities.

Highlights

Breit–Wheeler pair creation is an elementary process of quantum electrodynamics (QED) in which matter and antimatter are produced purely from light [1]
In this paper we have discussed the prospects for experimental observation of nonlinear Breit–Wheeler pair creation, using the collision between an intense laser pulse and the γ rays produced by bremsstrahlung of a laser wakefield acceleration (LWFA) electron beam in a high-Z target
We have shown that the thickness of the high-Z target L may be optimized to maximize the number of Breit–Wheeler positrons: across a broad range of experimentally accessible parameters, this is L Lrad = 0.7, where Lrad is the radiation length

Summary

Introduction

Breit–Wheeler pair creation is an elementary process of quantum electrodynamics (QED) in which matter and antimatter are produced purely from light [1]. The two-photon, or linear, process has yet to be detected experimentally, as it is difficult to achieve a collision between photon beams where the flux is sufficiently high and the per-particle centre-of-mass energy exceeds twice the electron mass Both these requirements have been met experimentally, and pair creation observed, in the multiphoton regime: [2] used Compton scattering of a 46.6 GeV electron beam in a laser pulse with strength parameter a0 = 0.36 to produce γ rays that subsequently interacted with further laser photons to produce electron–positron pairs [3]. By using a laser pulse with a0 > 10 as the target, we enter the strong-field regime where the pair creation probability increases non-perturbatively with the laser amplitude This will permit the positron yield to be substantially higher than reported by [2] despite the lower electron beam energies we consider. We find that the thickness of the high-Z target may be chosen to maximize the number of positrons that are produced in the laser pulse and discuss the importance of reducing the divergence of the γ ray beam

Probability of Breit–Wheeler pair creation

Bremsstrahlung photon generation

The positron yield and optimal target thickness

Findings

Summary