photodetachment and elastic electron-positronium scattering*

For energies below the Ps(n=2) threshold we have computed the photodetachment cross section of Ps^- in the length, velocity, and acceleration forms. In these calculations we used the ¹S bound-state wave function that we obtained from using the Rayleigh-Ritz variational method and the ¹P continuum wave function from the complex Kohn variational method. Prior calculations of this cross section have been performed for the length and velocity forms [1-5]. Using the Kohn, inverse Kohn, and complex Kohn variational methods we have determined the ^1,3S, ^1,3P and ^1,3D phase shifts for elastic electron-Ps scattering. We have computed the elastic differential, elastic integrated, momentum transfer, ortho-para conversion cross sections. In addition, using the ^1,3S  phase shifts and effective range theory formulas that explicitly take into account the polarization potential we have determined the singlet and triplet S-wave scattering lengths. We have also determined parameters for ¹S, ^1,3P and ^1,3D-wave resonances. We compare our results with other results found in the literature, such as those given in Refs. [1-5].

[1] S. J. Ward and M. R. C. McDowell, Europhys. Lett. 1, 167 (1986).

[2] S. J. Ward, Thesis, University of London, Unpublished (1986).

[3] S. J. Ward, J. W. Humberston and M. R. C. McDowell, J. Phys. B 30, 127 (1987).

[4] A. Igarashi, S. Nakazaki, and A. Ohsaki, Phys. Rev. A 61, 032710 (2000).

[5] A. Igarashi, I. Shimamura and N. Toshima, New J. Phys. 2, 17 (2000).