G G Ryzhikh and J Mitroy 2000 J. Phys. B: At. Mol. Opt. Phys. 33 2229 doi:10.1088/0953-4075/33/12/306
G G Ryzhikh1,2 and J Mitroy1,2
Show affiliationsThe transition amplitude for electron-positron annihilation during positron-hydrogen scattering is formulated in terms of the half-shell T-matrix elements obtained from a solution of the momentum space Lippmann-Schwinger equation. The derived expression is well defined at energies below the positronium (Ps) formation threshold. However, singularities in the transition amplitude exist at energies above the Ps-formation threshold. The annihilation parameter for positron-hydrogen scattering is computed in a variety of models at energies below the Ps-formation threshold. Calculations with the largest basis reproduce previous variational calculations of ZJeff for the J = 0 and 1 partial waves. Accurate values of ZJeff were also given for the J = 2, 3 and 4 partial waves to give a summed Zeff that is probably the most accurate so far reported.
Issue 12 (28 June 2000)
Received 15 February 2000, in final form 2 May 2000
G G Ryzhikh and J Mitroy 2000 J. Phys. B: At. Mol. Opt. Phys. 33 2229
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