Vortices in Ionization Collisions by Positron Impact

Abstract

The presence of vortices in the ionisation of hydrogen atoms by positrons at intermediate impact energies is investigated. The present findings show that a previously reported minima in the fully-differential cross section is the signature of a vortex in the continuum positron-electron-proton system. The behaviour of the real and imaginary parts of the complex-valued transition matrix is studied in order to determine and characterize the vortex in momentum space. The obtained information is translated to fully-differential ionisation cross sections, feasible of being measured with currently available techniques.

9 pages, 3 figures. Submitted to Journal of Physics B. Results for 200 eV impact energy and a discussion of the validity of the approximation employed have been added in this version