Polarization of high-energy electrons traversing a laser beam

Abstract

When polarized electrons traverse a region where the laser light is focused their polarization varies even if their energy and direction of motion are not changed. This effect is due to interference of the incoming electron wave and an electron wave scattered at zero angle. Equations are obtained which determine the variation of the electron density matrix, and their solutions are given. The change in the electron polarization depends not only on the Compton cross section but on the real part of the forward Compton amplitude as well. It should be taken into account, for example, in simulations of the e → γ conversion for future γγ colliders.

Resummation of quantum radiation reaction and induced polarization

“…Here we find that with RR there is still a nonzero degree of polarization asymptotically, but this asymptotic value is reached on a much shorter time scale and is significantly lower. For a circularly polarized monochromatic field and without RR, there is no induced polarization to leading order [11,16,17], because the loop cancels the contribution from photon emission. However, here we find that with RR there is a nonzero degree of polarization.…”

“…If one only considers the contribution from real photon emission then one would conclude that a circularly polarized field would be able to make the particles polarized along the propagation direction of the laser. However, at first order in α, this is exactly canceled by the the cross term between the zeroth order amplitude and the first-order loop [11,16,17] (see though [18] for dependence on collision angle). Hence, if one neglects RR then there is no induced polarization for a circularly polarized field.…”

“…Note that T includes a factor of a 0 in the constant field case (4), but not in the circular case(17).…”

The Photon Collider at Tesla

“…Variation of polarisation of unscattered electron [179]. Compton scattering changes the electron polarisation.…”

“…General formulae for this effect have been obtained in [179], where the variation in polarisation of the unscattered electrons was considered to be the result of the interference of the incoming electron wave with the wave scattered at zero angle.…”