Near-threshold behavior of positronium-antiproton scattering

Abstract

Using the convergent close-coupling theory we study the threshold behavior of cross sections for positronium (Ps) of energy E scattering on antiprotons. In the case of Ps(1s) elastic scattering, simple power laws are observed for all partial waves studied. The partial-wave summed cross section is nearly constant, and dominates the antihydrogen formation cross section at all considered energies, even though the latter is exothermic and behaves as 1/E 1/2 . For Ps(2s), oscillations spanning orders of magnitude on top of the 1/E behavior are found in the elastic and quasielastic cross sections. The antihydrogen formation is influenced by dipole-supported resonances below the threshold of inelastic processes. Resonance energies form a geometric progression relative to the threshold. The exothermic antihydrogen formation cross sections behave as 1/E at low energies, but are oscillation free. We demonstrate that all these rich features are reproduced by the threshold theory developed by Gailitis [J. Phys. B: At. Mol. Phys. 15, 3423 (1982)].

Simplified model to treat the electron attachment of complex molecules: Application to H2CN and the quest for the CN− formation mechanism

“…Therefore, our approach gives an upper bound of the DEA cross section within the Frank-Condon and WKB approximations. Also, the width is assumed to be on-shell, so that our approach would work only for systems with narrow resonances [55]. But if the width is narrow enough, the survival factor is closed to unity, so that the two limitations are in fact equivalent.…”

“…At zero electron energy, the classical turning point s E is around -1.4, such that the capture process occurs in a well-defined region of normal coordinates, thereby justifying our approach. Figure 4 shows the effective width against effective resonance energy ∆(s ε ), which is equal to electron energy ε in this approach as to enforce the threshold behavior [55]. The electronic structure calculations give the value 0.957 ea 0 for the permanent dipole moment of H 2 CN as at s 1 = 1.25.…”

“…Since the width of the resonance is narrow, we neglect the explicit energy dependence of the width, i.e., we only consider the on-shell width. In the so-called local complex potential approach [27,54,55], the metastable state ξ d becomes solution of the following equation…”

Recent progress in the description of positron scattering from atoms using the convergent close-coupling theory

“…(19), and presented just a combination that yielded somewhat reasonable agreement with the results of the "new" numerical method. The new technique also proved to be particularly advantageous in studying threshold phenomena in positronium-(anti)proton scattering [272]. (19).…”

Heating due to momentum transfer in low-energy positronium-antiproton scattering

“…Kadyrov et al [24] and Rawlins et al [25] presented data forH(n ′ l ′ ), formation with n ′ ≤ 4 upon Ps(nl)+p scattering with n ≤ 3. Fabrikant et al [26] analysed the threshold behavior in each partial wave L, and addressed issues associated with the degeneracy of the energy levels. This theoretical work was motivated by recent experimental progress.…”