Microscopic response effects in collisions of antiprotons with helium atoms and lithium ions

Abstract

We present total single- and double-ionization cross sections for the collision systems pbar + He and pbar + Li+ in the 1–1000 keV impact energy range with emphasis on microscopic response effects during the collision. The calculations rely on the basis generator method. In both collision systems, the response of the effective electronic interaction to the time-dependent density reduces the ionization cross section at low impact energies significantly. It is shown, in comparison with other theories, that this reduction is a consequence of time-dependent screening rather than due to dynamical correlation effects

Electrostatic ultra-low-energy antiproton recycling ring

“…Total ionisation cross section measurements for antiproton incident energies from 40 to 3,000 keV were reported over a decade ago [10,11]; above 100 keV incident energy, theory and experiment are in good agreement [7]. Several theoretical studies have predicted cross sectional trends in the low energy region (down to 1 keV) [12][13][14][15][16][17]. Whilst these theories all agree on the general trend towards increasing cross section from 1 to 70 keV, they vary considerably in the details of the shape and absolute value.…”

Effect of static electric field on cross sections in antiproton impact ionization of atomic helium

“…1. In the same figure, the calculated results of ionization cross sections are compared with the various experimental [3,4,6] as well as with the theoretical [10][11][12][13][14][15][16][17][18][19][20][21][22][23] results. From the experimental side, the present calculated data for ionization of the helium atom by antiproton are compared with experimental data of Andersen et al [4] who performed their experiment in the energy range from 40 keV to 3 MeV, Hvelpund et al [6] performed their experiment in the energy range from 13 to 500 keV and Knudsen et al [3] performed their experiment in the energy range from 3 to 25 keV.…”

“…From the experimental side, the present calculated data for ionization of the helium atom by antiproton are compared with experimental data of Andersen et al [4] who performed their experiment in the energy range from 40 keV to 3 MeV, Hvelpund et al [6] performed their experiment in the energy range from 13 to 500 keV and Knudsen et al [3] performed their experiment in the energy range from 3 to 25 keV. From the theoretical side, calculated results are compared with the results of McGovern et al [10] who performed their calculation using the coupled pseudosate (CP) impact-parameter method (IPM) with 165 (75) states in the energy range from 0.1 to 500 keV, Sahoo et al [13] performed their calculation using the semiclassical single center close coupling approach in the energy range from 10 to 1000 keV, Igarashi et al [22] performed their calculation using the close coupling method in the energy range from 10 to 1000 keV, Keim et al [14] performed their calculation using time-dependent density functional theory (TDDFT) in the energy range from 1 to 1000 keV with response and non-response BGM basis set, Kirchner et al [18] performed their calculation using an independent particle model (IPM) in the energy range from 1 to 1000 keV, Lee et al [20] performed their calculation the using semiclassical impact parameter close-coupling approximation in the energy range from 1 to 300 keV, Foster et al [11] performed their calculation using a nonperturbative time dependent close-coupling method in the energy range from 1 keV to 1 MeV, Schultz et al [15] performed their calculation using the lattice, time-dependent Schrodinger equation (LTDSE) method in the energy range from 1 to 1000 keV, Wehrman et al [23] performed their calculation using the independent particle model (IPE) and independent event model (IEV) in the energy range from 10 to 1000 keV. The present calculated results of the total ionization cross sections for helium atom and antiproton collision are in agreement with the available experimental [3,4,6] and theoretical [10,11,13,[14][15][16]18,[21][22][23] results in the entire energy range.…”

“…From the theoretical point of view, the collision between antiproton and the two-electron helium atom is a fundamental problem, which includes both static and dynamic correlations. There are many theoretical studies [10][11][12][13][14][15][16][17][18][19][20][21][22][23] on the single ionization by various approximations. But in those studies, investigators have been studied collisional ionization cross sections in the absence of the electric fields.…”

“…As antiproton beams become available at CERN for atomic collision experiments in 1986, a number of measurements [1][2][3][4][5][6][7] have been carried out at different energy ranges (from keV to MeV) for antimatter and matter collisions. At the same time, many theoretical studies [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] of antiproton and atom collision have also been started. Although collisions between antiproton and helium have been studied during the last decade, it is still a challenge to understand in detail even for the simplest collisional processes.…”