Positronium formation in p-wave positron-hydrogen scattering

Positronium formation in positron-hydrogen scattering

“…Experimentally it is not possible at present to determine the excited-state Ps formation cross sections separately, hence the need for accurate theoretical predictions. Elaborate calculations, using the Kohn variational method, have been reported by Humberston (1984) and Brown andHumberston (1984, 1985) for the s, p and d partial waves in e t + H scattering below 10.2 eV, and these are probably the most accurate results available in this region. Winick and Reinhardt (1978) have used the moment T-matrix method to produce results for all partial waves up to I = 5, in the energy range 0.25-1.15 au.…”

A Simple Model for Positronium Formation in Positron – Hydrogen Atom Collisions

“…In Fig. 1 the calculated total Ps-formation cross section is compared with the experimental results of Zhou et al [9] along with prior measurements of Weber et al [10] and several theoretical values [5][6][7][8]13] as a function of the positron energy. The measured σ Ps 's and most of the calculated values follow a rather smooth, bell-like, structureless curve.…”

“…The B1 approximation calculations of Massey and Mohr [5] and the Fock-Tani calculations of Straton [13] predict cross sections which peak at an energy 3 eV lower than the measurements and with magnitudes greater by about 35% and 50%, respectively. The accurate Kohn variational calculations of Brown and Humberston [6] are restricted to low incident energies, but Weber et al [10] note that the extrapolation of these predictions to higher energies does not appear inconsistent with the size and energy location of observed maximum in σ Ps . The σ Ps values measured by Zhou et al [9] are reasonably consistent with the prior experimental result [10] and are in very good agreement with the coupled 33-state calculation of Kernoghan et al [7] and with the 28-state close-coupling approximation by Mitroy [8] (except at energies below the Ps-formation threshold).…”

“…The σ Ps values measured by Zhou et al [9] are reasonably consistent with the prior experimental result [10] and are in very good agreement with the coupled 33-state calculation of Kernoghan et al [7] and with the 28-state close-coupling approximation by Mitroy [8] (except at energies below the Ps-formation threshold). [5]; thin solid line, Brown and Humberston [6]; short broken curve, Kernoghan et al [7]; long broken curve, Mitroy [8]; full curve with dots, Straton [13]. Experiment: circles, Zhou et al [9]; squares, Weber et al [10].…”

“…This theory is based on the first Born approximation (B1), and has been applied at the first time in 1954 by Massey and Mohr [5] for positronium (Ps) formation in positronhydrogen collision. In spite of the fact, that more sophisticated methods [6][7][8] give more accurate results for the total Ps-formation cross section, the Bethe theory has the advantage of following analytical expressions for the elastic scattering, excitation, ionization and the positronium-formation cross sections. The annihilation process cannot be treated in this model, because it is significant only at very low impact energies of the positron, where the Born approximation cannot be applied.…”