Deep minimum in the Coulomb-Born TDCS for electron-impact ionization of atomic hydrogen

Recently, Macek {\it et al.} attributed a deep minimum in the triply differential cross section (TDCS) for electron impact ionization of helium to a vortex [1]. Vortices have been shown to be present for positron-impact ionization of atomic hydrogen [2]. Using the Coulomb-Born approximation [3] we have obtained a deep minimum in the TDCS for electron-impact ionization of atomic hydrogen for an incident energy of 76.45 eV and for the doubly symmetric coplanar geometry. At the scattering angle where there is a minimum in the TDCS, the real and imaginary parts of the transition matrix element are zero. [1] J. H.Macek, J. B. Sternberg, S. Y. Ovchinnikov and J. S. Briggs, Phys. Rev. Lett. {\bf 104}, 033201 (2010). [2] F. Navarrete and R. O. Barrachina, J. Phys. B {\bf 48}, 055201 (2015). [3] J. Botero and J. H. Macek, Phys. Rev. A {\bf 45}, 154 (1992).