Probing strong-field QED via angle-discriminated emissions from electrons traversing colliding laser pulses

Future laser-electron colliders will reach quantum parameters <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mi>χ</a:mi> </a:math> well in excess of unity, enabling studies of strong-field QED in extreme regimes. However, statistical inference in such experiments requires mitigating premature radiative losses of electrons to enable high- <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mi>χ</b:mi> </b:math> QED events, as well as separating the detectable signal of these events from that of lower- <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mi>χ</c:mi> </c:math> particles and photons produced by QED cascades. We propose a collider geometry in which electrons traverse the waist of two or four perpendicularly propagating, tightly focused laser pulses. This configuration suppresses both outlined difficulties by leveraging the short interaction length of the waist, rather than relying on the more technically demanding reduction of pulse duration. Moreover, altering the phase and polarization of each pulse causes the electrons to undergo helical motion where the deflection angle is correlated with the field strength, permitting an angle-based discrimination of the signal from high- <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mi>χ</d:mi> </d:math> events. Analysis and simulations show that the case of four circularly polarized pulses uniquely permits achieving helical motion throughout the entire focal region, leading to near-perfect high- <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:mi>χ</e:mi> </e:math> angle-discrimination and thereby high signal-to-noise ratio. These findings support the consideration of the proposed concept as a viable layout for future experiments at PW laser facilities.