Generation of polarized positron beams via collisions of ultrarelativistic electron beams

TL;DR

This paper proposes a new method to generate highly polarized positron beams using colliding ultrarelativistic electron beams, employing particle simulations to demonstrate polarization above 40% within femtoseconds.

Contribution

A novel scheme utilizing multiphoton Breit-Wheeler process and beam configuration to produce polarized positrons, with detailed simulation analysis of polarization control.

Findings

Positron polarization exceeds 40% in femtoseconds.

The polarization can be increased to 60% with proper initial seeding beam polarization.

The scheme is robust against parameter variations.

Abstract

A novel scheme is proposed for generating a polarized positron beam via multiphoton Breit-Wheeler process during the collision of a 10 GeV, pC seeding electron beam with the other 1 GeV, nC driving electron beam. The driving beam provides the strong self-generated field, and a suitable transverse deviation distance between two beams enables the field experienced by the seeding beam to be unipolar, which is crucial for realizing the positron polarization. We employ the particle simulation with a Monte-Carlo method to calculate the spin- and polarization-resolved photon emission and electron-positron pair production in the local constant field approximation. Our simulation results show that a highly polarized positron beam with polarization above $40\%$ can be generated in several femtoseconds, which is robust with respect to parameters of two electron beams. Based on an analysis of the influence of $\gamma$-photon polarization on the polarized pair production, we find that a polarized seeding beam of the proper initial polarization can further improve the positron polarization to $60\%$.