Coincidence studies of He ionized byC6+,Au24+, and

Mark E. McGovern

¹

,

Denise Assafrão

²

,

José R. Mohallem

³

et al.

Abstract

A recently developed [Phys. Rev. A 79, 042707 (2009)] impact parameter coupled pseudostate approximation (CP) is applied to calculate triple differential cross sections for single ionization of He by C 6+ , Au 24+ , and Au 53+ projectiles at impact energies of 100 and 2 MeV/amu for C 6+ and 3.6 MeV/amu for Au 24+ and Au 53+ . For C 6+ , satisfactory, but not perfect, agreement is found with experimental measurements in coplanar geometry, but there is substantial disagreement with data taken in a perpendicular plane geometry. The CP calculations firmly contradict a projectile-nucleus interaction model which has been used to support the perpendicular plane measurements. For Au 24+ and Au 53+ , there is a complete lack of accord with the available experiments. However, for Au 24+ the theoretical position appears to be quite firm with clear indications of convergence in the CP approximation and very good agreement between CP and the completely different three-distorted-waves eikonal-initial-state (3DW-EIS) approximation. The situation for Au 53+ is different. At the momentum transfers at which the measurements were made, there are doubts about the convergence of the CP approximation and a factor of 2 difference between the CP and 3DW-EIS predictions. The discord between theory and experiment is even greater with the experiment giving cross sections a factor of 10 larger than the theory. A study of the convergence of the CP approximation shows that it improves rapidly with reducing momentum transfer. As a consequence, lower-order cross sections than the triple are quite well converged and present an opportunity for a more reliable test of the experiment.

Fully differential cross sections for singly ionizing 1-MeV p +He collisions at small momentum transfer: Beyond the first Born approximation

“…This finding was particularly surprising given the fact that the measurements were carried out under kinematical conditions which are believed to be perfectly suitable for applicability of perturbative approaches: (i) |Z p |/v p = 0.1 a.u., where Z p and v p are the projectile charge and velocity, respectively, and (ii) small energy-and momentum-transfer values. Further discussions involved various attempts to explain the source of the discrepancies in the nodal structure, ranging from higher-order [4][5][6][7][8] and non-perturbative mechanisms [7,[9][10][11][12]] to experimental uncertainties [8,13] and so-called projectile coherence effects [14]. Though the explanation due to experimental uncertainties alone was refuted in [15], the very recent 1-MeV p+He experiment at momentum transfer of 0.75 a.u.…”

Relativistic calculations of differential ionization cross sections: Application to antiproton-hydrogen collisions

“…[16][17][18]. Recently these FDCS have also been studied by several nonperturbative methods [19][20][21][22][23]. Firstly, McGovern et al [19,20] developed a method for extracting the FDCS from an impact-parameter treatment of the collision within a coupled pseudostate (CP) formalism.…”

Ionization of helium by slow antiproton impact: Total and differential cross sections

“…This disagreement was, for the most part, resolved by two-active electron approaches [11][12][13][14] which are in relatively good agreement with each other and with the experimental data. Further improvements of the SI and double ionization (DI) cross sections were achieved by extensive ab initio calculations using the coupled-pseudostates (CP) [8,15], the convergent close-coupling (CCC) [9], the timedependent close-coupling (TDCC) [6,7], and the timedependent density functional theory (TDDFT) [14,16] * sandor.borbely@phys.ubbcluj.ro methods. However, discrepancies between the different approaches remain and call for further investigations (for a comprehensive overview of recent work see the review by Kirchner and Knudsen [5]).…”

“…Except for the work by McGovern et al [8,15], all recent calculations focused on total ionization cross sections. However, for the design of future differential cross section measurements [5], predictions for differential ionization cross sections are desirable.…”