Generation of arbitrarily polarized GeV lepton beams via nonlinear Breit-Wheeler process

Generation of arbitrarily spin-polarized electron and positron beams has been investigated in the single-shot interaction of high-energy polarized <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>γ</mml:mi></mml:math> -photons with an ultraintense asymmetric laser pulse via nonlinear Breit-Wheeler pair production. We develop a fully spin-resolved semi-classical Monte Carlo method to describe the pair creation and polarization. In the considered general setup, there are two sources of the polarization of created pairs: the spin angular momentum transfer from the polarized parent <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>γ</mml:mi></mml:math> -photons, as well as the asymmetry and polarization of the driving laser field. This allows to develop a highly sensitive tool to control the polarization of created electrons and positrons. Thus, dense GeV lepton beams with average polarization degree up to about <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>80</mml:mn> <mml:mo>%</mml:mo></mml:mrow> </mml:math> , adjustable continuously between the transverse and longitudinal components, can be obtained by our all-optical method with currently achievable laser facilities, which could find an application as injectors of the polarized <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow><mml:msup><mml:mi>e</mml:mi> <mml:mo>+</mml:mo></mml:msup> <mml:msup><mml:mi>e</mml:mi> <mml:mo>-</mml:mo></mml:msup> </mml:mrow> </mml:math> collider to search for new physics beyond the Standard Model.