Formation of positronium ine++H−collisions

Abstract

Cross sections for positronium formation by capture from the negative hydrogen ion are given. Orthogonalization corrections to the Coulomb (first-order) Born approximation (CBA) difFerential and total cross sections are calculated using approximate H wave functions of both Lowdin [Phys. Rev. 90, 123 (1953)] and Chandrasekhar [Astrophys. J. 100, 176 (1944)]. The present calculation of the CBA cross sections using the post interaction for Lowdin's wave function (LCBAPS) disagrees with the calculation of Choudhury, Mukherjee, and Sural (CMS) [Phys. Rev. A 38, 2358], whereas our results using the prior interaction agree. Thus, where CMS found an order of magnitude post-prior discrepancy in the differential cross sections except at forward angles, and a markedly different shape to the minima. , the present post, and prior results differ by 1 -10'K at 100 eV, and the minima have the same shape and occur within one degree of each other. Chandrasekhar's "open-shell" wave function, which is superior to Lowdin's in bound-state problems since it gives a negative binding energy, gives post and prior cross sections that are almost indistinguishable at this energy and are 2 to 3 as large as the LCBA. Various methods of orthogonalizing the unbound projectile to the possible bound states are considered. It is found that treating the atomic nuclei as if they were isotopic spin projections [Straton and Girardeau, Phys. Rev. A 40, 2991 (1989)] of a single type of "nucleon" gives cross sections that are an improvement over the CBA. PACS number(s): 34.70.+e, 34.10+x,36.10.Dr

$\bar {\sf {H}}^{+}$ ion production from collisions between antiprotons and excited positronium: cross sections calculations in the framework of the GBAR experiment

“…Straton and Drachman used the Coulomb Born approximation (CBA) with two wave functions for H − to compute the cross sections of equation (3) at four different positron energies (0.1, 0.5, 1 and 100 eV) when Ps and H are in their ground states [16]. Chaudhuri [17] highlighted the importance of the choice of the H − wave function and demonstrated the influence of the correlation description on the total cross section above 50 eV positron energy.…”

“…Chaudhuri [17] highlighted the importance of the choice of the H − wave function and demonstrated the influence of the correlation description on the total cross section above 50 eV positron energy. Biswas [18] used the two-channel exchange coupled-channel theory to compute the cross section of the reverse process studied in [16], but took a plane wave for the exit channel and thus did not take into account the long range Coulomb interaction between e + and H − . This resulted in a total cross section going to zero close to the threshold when a finite value is expected.…”

Formation of positron-atom bound states in collisions between Rydberg Ps and neutral atoms

“…In every case, the computed value of I was found to be within 10 −8 of the exact value I = 1. With the linear grid it is necessary to use such a large number of points because the function F nl possesses n − l − 1 nodes, so for Rydberg states with large n and small l, F nl (p) oscillates rapidly at small p. Solid purple curve, present; blue circle with error bars, CBA [63]; dot-dash-dotted yellow curve, 2CC [55]; dot-dashed blue curve, CMEA [58]; short-dashed green curve, CDW-FS [61]; dotted orange curve, CPA [64]; long-dashed red curve, DWBA (see text).…”

“…The aim of the theoretical part of this work is to obtain estimates of the cross sections of reaction (2) Solid purple curve, present; blue circle with error bars, CBA [63]; dot-dash-dotted yellow curve, 2CC [55]; dot-dashed blue curve, CMEA [58]; short-dashed green curve, CDW-FS [61]; dotted orange curve, CPA [64]; long-dashed red curve, DWBA (see text).…”

“…Most recently, Comini and Hervieux [60] and Comini et al [61] computed the cross section for Ps(nl)-H(n l ) collisions using the continuum-distorted-wave-final-state (CDW-FS) method; they considered n = 1-3 and n = 1-5. Additionally, there exist calculations [62][63][64][65] for the reverse reactions…”