Positronium formation in then=2 level in positron scattering from hydrogen and helium atoms

Positronium formation for positron scattering from hydrogen: Maximum positions and scaling law

“…As seen from the figure, the present results accord with their calculations very well at energies below 23 eV. The results of PODWA [10] and DWA [7] (only 2s) models are also shown in this figure. As in the process of Ps(1s) formation, the DWA model overestimates the cross sections at low-energy range.…”

“…For the simplest case of positron-hydrogen collision, the experimental measurement of Ps formation cross section is now amenable and reliable results have been obtained [3,4]. On the theoretical side, the Ps formation process has been widely investigated by several perturbation methods, such as the first-and second-order Born (FBA and SBA) [5,6], first and second distorted-wave approximations (DWA and SDWA) [7,8], polarized-orbital distorted-wave approximation (PODWA) [9,10], and the continuum distorted-wave (CDW) [11][12][13][14] methods. The more elaborate close-coupling (CC) methods have also been successfully applied to investigate the Ps formation process in positron-hydrogen collision.…”

e++ H(ns) → Ps(n′s) + p for arbitrarynandn′

“…In this paper we extend this DWT to study positronium formation in an arbitrary s-state from an arbitrary s-state of the hydrogen atom by positron impact. Calculations for such processes have rarely been reported in the literature except using the first Born approximation (FBA), and a few accurate calculations [3][4][5][6][7] have been performed at low energies to study 1s-2s and 1s-2p capture processes in positron-hydrogen collisions.…”

Excited-State Positronium Formation from Helium, Argon, and Xenon

“…A decade later, using a similar method, Ps à was also observed in low density gases (namely, Ne, Ar, and H 2 ) formed by positron projectiles of a few tens of eV [14]. While formation cross sections for Ps in the 2S and 2P states have been theoretically calculated for H (e.g., [15]), He [16][17][18][19][20], and the noble gases [21], experimental determinations have been lacking until now. It was recently considered that structure observed in the total positronium formation cross section (Q Ps ) for the heavier noble gases might be due to Ps à [22][23][24], and estimates were made which inferred increasing contributions from Ps à to Q Ps as the target atomic number was increased from He to Xe [22].…”

“…[17,20], the distorted-wave approach of Ref. [16], and from 100 eV, the second Born approximation of Ref. [18].…”