## Abstract

The 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 Z_{eff}^{J} for the J = 0 and 1 partial waves. Accurate values of Z_{eff}^{J} were also given for the J = 2, 3 and 4 partial waves to give a summed Z_{eff} that is probably the most accurate so far reported.

Original language | English |
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Pages (from-to) | 2229-2243 |

Number of pages | 15 |

Journal | Journal of Physics B: Atomic, Molecular and Optical Physics |

Volume | 33 |

Issue number | 12 |

DOIs | |

Publication status | Published - 28 Jun 2000 |