Multi-cut forced impulse method single-ionization cross sections for slow antiprotons on helium

Abstract

We present multi-cut forced impulse method cross sections for the single ionization of helium by antiprotons in the energy range 12-200 keV amu −1 . Eight segmented time intervals, bracketed by collapse onto fully correlated states, are needed to establish convergence in the effects of intermediate dynamic correlation. At low energies the theoretical cross sections fail to reproduce experiments. We point out that a similar situation obtains for the antiprotonhydrogen system.We take great pleasure in dedicating this letter to Richard Lemmer on the occasion of his 65th birthday.

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

“…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. The largest discrepancy is observed at energies below 40 keV, where our calculated cross sections are twice in the magnitude, but the nature of variation is similar to that of previous results.…”

“…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.…”

“…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.…”

“…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.…”

On the measurement of ionization cross sections for antiproton impact on atoms and molecules

“…This difference is now well understood, see e.g. [12] as being due to an interference between several different channels each leading to double ionization: In one, the so-called "Two Step One (TS1)" the projectile interacts only once, namely with one target electron, which then interacts with another, causing both to be ejected. Or the second electron is promoted to the continuum after the removal of the first in a "Shake Off (SO)" process.…”