Application of the Hyperspherical Hidden Crossing Method to Near-Threshold Positron-Hydrogen Ionization

We have applied the hyperspherical hidden crossing method [1] to compute the S-wave cross section for near-threshold e$^+$-H ionization. We confirm the second order correction terms to the Wannier threshold law that were previously derived [2]. The small S-wave cross section is due to destructive interference between the two amplitudes that correspond to different paths leading to Ps formation. \newline \newline [1] J. H. Macek and S. Yu.Ovchinnikov, Phys. Rev. A {\bf 54}, 544 (1996). \newline [2] W. Ihra, J. H. Macek, F. Mota-Furtado and P. F. O'Mahony, Phys. Rev. Lett. {\bf 78}, 4027 (1997), James Sternberg, S. J. Ward, J. H. Macek and J. Shertzer, Bull. Am. Phys. Soc. {\bf 49}, no.3, p.52 (2004).