Vortex kinematics of a continuum electron pair

The form of the helium (e, 2e) scattering amplitude near a recently identified vortex singularity in the electron-pair continuum is derived by considering the angular momentum of the electron pair about the vortex. A threshold-like analytic expansion in cylindrical partial waves of the electron pair about the vortex is established, and good fits to the cross section near the vortex are demonstrated with just the two lowest partial waves. (fast track communication)