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Articles 31 - 60 of 63
Full-Text Articles in Physical Sciences and Mathematics
Tracing Multiple Scattering Patterns In Absolute (E, 2e) Cross Sections For H₂ And He Over A 4Π Solid Angle, Xueguang Ren, Arne Senftleben, Thomas Pflüger, Alexander Dorn, James Colgan, Michael S. Pindzola, Ola A. Al-Hagan, Don H. Madison, Igor Bray, Dmitry V. Fursa, Joachim Hermann Ullrich
Tracing Multiple Scattering Patterns In Absolute (E, 2e) Cross Sections For H₂ And He Over A 4Π Solid Angle, Xueguang Ren, Arne Senftleben, Thomas Pflüger, Alexander Dorn, James Colgan, Michael S. Pindzola, Ola A. Al-Hagan, Don H. Madison, Igor Bray, Dmitry V. Fursa, Joachim Hermann Ullrich
Physics Faculty Research & Creative Works
Absolutely normalized (e,2e) measurements for H2 and He covering the full solid angle of one ejected electron are presented for 16 eV sum energy of both final state continuum electrons. For both targets rich cross-section structures in addition to the binary and recoil lobes are identified and studied as a function of the fixed electron's emission angle and the energy sharing among both electrons. For H2 their behavior is consistent with multiple scattering of the projectile as discussed before. For He the binary and recoil lobes are significantly larger than for H2 and partly cover the multiple …
Dynamical (E, 2e) Studies Using Tetrahydrofuran As A Dna Analog, Christopher J. Colyer, Susan M. Bellm, B. Lohmann, G. Friedrich Hanne, Ola A. Al-Hagan, Don H. Madison, Chuangang Ning
Dynamical (E, 2e) Studies Using Tetrahydrofuran As A Dna Analog, Christopher J. Colyer, Susan M. Bellm, B. Lohmann, G. Friedrich Hanne, Ola A. Al-Hagan, Don H. Madison, Chuangang Ning
Physics Faculty Research & Creative Works
Triple differential cross sections for the electron-impact ionization of the outer valence orbital of tetrahydrofuran have been measured using the (e, 2e) technique. The measurements have been performed with coplanar asymmetric kinematics, at an incident electron energy of 250 eV and at an ejected electron energy of 10 eV, over a range of momentum transfers. The experimental results are compared with theoretical calculations carried out using the molecular three-body distorted wave model. The results obtained are important for gaining an understanding of electron driven processes at a molecular level and for modeling energy deposition in living tissue.
Self-Imaging Of Molecules From Diffraction Spectra By Laser-Induced Rescattering Electrons, Junliang Xu, Zhangjin Chen, Anh-Thu Le, C. D. Lin
Self-Imaging Of Molecules From Diffraction Spectra By Laser-Induced Rescattering Electrons, Junliang Xu, Zhangjin Chen, Anh-Thu Le, C. D. Lin
Physics Faculty Research & Creative Works
We study high-energy angle-resolved photoelectron spectra of molecules in strong fields. In an oscillating laser electric field, electrons released earlier in the pulse may return to recollide with the target ion, in a process similar to scattering by laboratory prepared electrons. If midinfrared lasers are used, we show that the images generated by the returning electrons are similar to images observed in typical gas-phase electron diffraction (GED). These spectra can be used to retrieve the positions of atoms in a molecule as in GED. Since infrared laser pulses of durations of a few femtoseconds are already available today, the study …
Correlated Two-Photon Emission By Transitions Of Dirac-Volkov States In Intense Laser Fields: Qed Predictions, Erik Lotstedt, Ulrich D. Jentschura
Correlated Two-Photon Emission By Transitions Of Dirac-Volkov States In Intense Laser Fields: Qed Predictions, Erik Lotstedt, Ulrich D. Jentschura
Physics Faculty Research & Creative Works
In an intense laser field, an electron may decay by emitting a pair of photons. The two photons emitted during the process, which can be interpreted as a laser-dressed double Compton scattering, remain entangled in a quantifiable way: namely, the so-called concurrence of the photon polarizations gives a gauge-invariant measure of the correlation of the hard gamma rays. We calculate the differential rate and concurrence for a backscattering setup of the electron and photon beam, employing Volkov states and propagators for the electron lines, thus accounting nonperturbatively for the electron-laser interaction. The nonperturbative results are shown to differ significantly compared …
Measurement Of Bottom Versus Charm As A Function Of Transverse Momentum With Electron-Hadron Correlations In P Þ P Collisions At Square Root Of S = 200 Gev, Andrew Marshall Adare, Sergey V. Afanasiev, Christine A. Aidala, N. N. Ajitanand, Yasuyuki Akiba, Gyöngyi Baksay, László A. Baksay, Marcus Hohlmann, S. Rembeczki, Klaus Dehmelt
Measurement Of Bottom Versus Charm As A Function Of Transverse Momentum With Electron-Hadron Correlations In P Þ P Collisions At Square Root Of S = 200 Gev, Andrew Marshall Adare, Sergey V. Afanasiev, Christine A. Aidala, N. N. Ajitanand, Yasuyuki Akiba, Gyöngyi Baksay, László A. Baksay, Marcus Hohlmann, S. Rembeczki, Klaus Dehmelt
Aerospace, Physics, and Space Science Faculty Publications
The momentum distribution of electrons from semileptonic decays of charm and bottom quarks for midrapidity jyj < 0:35 in p þ p collisions at ffiffi s p ¼ 200 GeV is measured by the PHENIX experiment at the Relativistic Heavy Ion Collider over the transverse momentum range 2 < pT < 7 GeV=c. The ratio of the yield of electrons from bottom to that from charm is presented. The ratio is determined using partial D=D ! e KX (K unidentified) reconstruction. It is found that the yield of electrons from bottom becomes significant above 4 GeV=c in pT. A fixed-order-plus-next-to-leading-log perturbative quantum chromodynamics calculation agrees with the data within the theoretical and experimental uncertainties. The extracted total bottom production cross section at this energy is bb ¼ 3:2þ1:2 1:1ðstatÞ þ1:4 1:3ðsystÞb.
Hydrodynamic Relaxation Of An Electron Plasma To A Near-Maximum Entropy State, D. J. Rodgers, S. Servidio, W. H. Matthaeus, D. C. Montgomery, T. B. Mitchell, T. Aziz
Hydrodynamic Relaxation Of An Electron Plasma To A Near-Maximum Entropy State, D. J. Rodgers, S. Servidio, W. H. Matthaeus, D. C. Montgomery, T. B. Mitchell, T. Aziz
Dartmouth Scholarship
Dynamical relaxation of a pure electron plasma in a Malmberg-Penning trap is studied, comparing experiments, numerical simulations and statistical theories of weakly dissipative two-dimensional (2D) turbulence. Simulations confirm that the dynamics are approximated well by a 2D hydrodynamic model. Statistical analysis favors a theoretical picture of relaxation to a near-maximum entropy state with constrained energy, circulation, and angular momentum. This provides evidence that 2D electron fluid relaxation in a turbulent regime is governed by principles of maximum entropy.
Accurate Retrieval Of Target Structures And Laser Parameters Of Few-Cycle Pulses From Photoelectron Momentum Spectra, Samuel Micheau, Zhangjin Chen, Anh-Thu Le, J. Rauschenberger, M. F. Kling, C. D. Lin
Accurate Retrieval Of Target Structures And Laser Parameters Of Few-Cycle Pulses From Photoelectron Momentum Spectra, Samuel Micheau, Zhangjin Chen, Anh-Thu Le, J. Rauschenberger, M. F. Kling, C. D. Lin
Physics Faculty Research & Creative Works
We illustrate a new method of analyzing three-dimensional momentum images of high-energy photoelectrons generated by intense phase-stabilized few-cycle laser pulses. Using photoelectron momentum spectra that were obtained by velocity-map imaging of above-threshold ionization of xenon and argon targets, we show that the absolute carrier-envelope phase, the laser peak intensity, and pulse duration can be accurately determined simultaneously (with an error of a few percent). We also show that the target structure, in the form of electron-target ion elastic differential cross sections, can be retrieved over a range of energies. The latter offers the promise of using laser-generated electron spectra for …
Quantitative Rescattering Theory For Nonsequential Double Ionization Of Atoms By Intense Laser Pulses, Samuel Micheau, Zhangjin Chen, Anh-Thu Le, C. D. Lin
Quantitative Rescattering Theory For Nonsequential Double Ionization Of Atoms By Intense Laser Pulses, Samuel Micheau, Zhangjin Chen, Anh-Thu Le, C. D. Lin
Physics Faculty Research & Creative Works
Laser-induced electron recollisions are fundamental to many strong field phenomena in atoms and molecules. Using the recently developed quantitative rescattering theory, we demonstrate that the nonsequential double ionization (NSDI) of atoms by lasers can be obtained quantitatively in terms of inelastic collisions of the target ions with the free returning electrons where the latter are explicitly given by a spectrum-characterized wave packet. Using argon atoms as target, we calculated the NSDI yield including contributions from direct (e,2e) electron-impact ionization and electron-impact excitation accompanied by subsequent field ionization. We further investigate the dependence of total NSDI on the carrier-envelope phase of …
Differential Cross Sections For The Ionization Of Oriented H₂ Molecules By Electron Impact, James Colgan, Michael S. Pindzola, Francis J. Robicheaux, Christian V. Kaiser, Andrew James Murray, Don H. Madison
Differential Cross Sections For The Ionization Of Oriented H₂ Molecules By Electron Impact, James Colgan, Michael S. Pindzola, Francis J. Robicheaux, Christian V. Kaiser, Andrew James Murray, Don H. Madison
Physics Faculty Research & Creative Works
A nonperturbative close-coupling technique is used to calculate differential cross sections for the electron-impact ionization of H2 at an energy of 35.4 eV. Our approach allows cross sections for any orientation of the molecule with respect to the incident electron beam to be analyzed. New features in the resulting cross sections are found compared with the case where the molecular orientation is averaged, and also with cross sections for He at equivalent electron kinematics. When averaged over all possible molecular orientations, good agreement is found with recent experimental results.
Laser Channeling Of Bethe-Heitler Pairs, Erik Lotstedt, Ulrich D. Jentschura, Christoph H. Keitel
Laser Channeling Of Bethe-Heitler Pairs, Erik Lotstedt, Ulrich D. Jentschura, Christoph H. Keitel
Physics Faculty Research & Creative Works
Electron-positron pair creation is analyzed for an arrangement involving three external fields: a high-frequency gamma photon, the Coulomb field of a nucleus, and a strong laser wave. The frequency of the incoming gamma photon is assumed to be larger than the threshold for pair production in the absence of a laser, and the peak electric field of the laser is assumed to be much weaker than Schwinger's critical field. The total number of pairs produced is found to be essentially unchanged by the laser field, while the differential cross section is drastically modified. We show that the laser can channel …
Double Ionization Of Helium By Ion Impact Analyzed Using Four-Body Dalitz Plots, M. F. Ciappina, Michael Schulz, T. Kirchner, Daniel Fischer, R. Moshammer, J. D. Ullrich
Double Ionization Of Helium By Ion Impact Analyzed Using Four-Body Dalitz Plots, M. F. Ciappina, Michael Schulz, T. Kirchner, Daniel Fischer, R. Moshammer, J. D. Ullrich
Physics Faculty Research & Creative Works
We have performed experimental and theoretical studies of double ionization of helium by 6 MeV proton impact using a recently developed tool, four-particle Dalitz plots [Schulz et al., J. Phys. B 22, 3091 (2007)] which enable the representation of multiple differential cross sections as a function of all four fragments in a single spectrum without loss of any part of the total cross section. As a result, the relative importance of the various interactions between the fragments can be studied in great detail. Comparisons of experimental data with theoretical first-order calculations and simulations for the higher-order (TS-2) process show that …
Alignment Of Heavy Few-Electron Ions Following Excitation By Relativistic Coulomb Collisions, Andrey S. Surzhykov, Ulrich D. Jentschura, Th H. Stohlker, Alexandre Gumberidze, Stephan Fritzsche
Alignment Of Heavy Few-Electron Ions Following Excitation By Relativistic Coulomb Collisions, Andrey S. Surzhykov, Ulrich D. Jentschura, Th H. Stohlker, Alexandre Gumberidze, Stephan Fritzsche
Physics Faculty Research & Creative Works
The Coulomb excitation of highly charged few-electron ions in relativistic collisions with protons and low- Z atoms is studied within the framework of first-order perturbation theory and the multiconfiguration Dirac-Fock method. Apart from the computation of the total excitation cross sections, a detailed theoretical analysis has been performed for the magnetic sublevel population of the residual ions. To describe this population, general expressions are derived for the alignment parameters of the excited states of the ions, taking into account the relativistic and many-electron effects. Calculations are performed for the K→L and K→M excitation of helium- and lithiumlike uranium ions and …
Long-Time Electron Spin Storage Via Dynamical Suppression Of Hyperfine-Induced Decoherence In A Quantum Dot, Wenxian Zhang, N. P. Konstantinidis, V. V. Dobrovitski, B. N. Harmon, Lea F. Santos, Lorenza Viola
Long-Time Electron Spin Storage Via Dynamical Suppression Of Hyperfine-Induced Decoherence In A Quantum Dot, Wenxian Zhang, N. P. Konstantinidis, V. V. Dobrovitski, B. N. Harmon, Lea F. Santos, Lorenza Viola
Dartmouth Scholarship
The coherence time of an electron spin decohered by the nuclear spin environment in a quantum dot can be substantially increased by subjecting the electron to suitable dynamical decoupling sequences. We analyze the performance of high-level decoupling protocols by using a combination of analytical and exact numerical methods, and by paying special attention to the regimes of large interpulse delays and long-time dynamics, which are outside the reach of standard average Hamiltonian theory descriptions. We demonstrate that dynamical decoupling can remain efficient far beyond its formal domain of applicability, and find that a protocol exploiting concatenated design provides best performance …
Potential For Ultrafast Dynamic Chemical Imaging With Few-Cycle Infrared Lasers, Toru Morishita, Anh-Thu Le, Zhangjin Chen, C. D. Lin
Potential For Ultrafast Dynamic Chemical Imaging With Few-Cycle Infrared Lasers, Toru Morishita, Anh-Thu Le, Zhangjin Chen, C. D. Lin
Physics Faculty Research & Creative Works
We studied the photoelectron spectra generated by an intense few cycle infrared laser pulse. By focusing on the angular distributions of the back rescattered high energy photoelectrons, we show that accurate differential elastic scattering cross-sections of the target ion by free electrons can be extracted. Since the incident direction and the energy of the free electrons can be easily changed by manipulating the laser's polarization, intensity and wavelength, these extracted elastic scattering cross-sections, in combination with more advanced inversion algorithms, may be used to reconstruct the effective single-scattering potential of the molecule, thus opening up the possibility of using few-cycle …
Isotope Shift In The Dielectronic Recombination Of Three-Electron ANd⁵⁷⁺, Carsten Brandau, Ch Kozhuharov, Zoltan Harman, Alfred K. Muller, Stefan Schippers, S. Kozhedub, Dietrich Bernhardt, Stefan Bohm, J. Jacobi, Eric W. Schmidt, Paul H. Mokler, Fritz J. Bosch, Heinz Jurgen Kluge, Th H. Stohlker, Klaus Beckert, P. Beller, Fritz Nolden, Markus Steck, Alexandre Gumberidze, Regina Reuschl, Uwe Spillmann, Fred John Currell, I. I. Tupitsyn, Vladimir M. Shabaev, Ulrich D. Jentschura
Isotope Shift In The Dielectronic Recombination Of Three-Electron ANd⁵⁷⁺, Carsten Brandau, Ch Kozhuharov, Zoltan Harman, Alfred K. Muller, Stefan Schippers, S. Kozhedub, Dietrich Bernhardt, Stefan Bohm, J. Jacobi, Eric W. Schmidt, Paul H. Mokler, Fritz J. Bosch, Heinz Jurgen Kluge, Th H. Stohlker, Klaus Beckert, P. Beller, Fritz Nolden, Markus Steck, Alexandre Gumberidze, Regina Reuschl, Uwe Spillmann, Fred John Currell, I. I. Tupitsyn, Vladimir M. Shabaev, Ulrich D. Jentschura
Physics Faculty Research & Creative Works
Isotope shifts in dielectronic recombination spectra were studied for Li-like ANd57+ ions with A = 142 and A = 150. From the displacement of resonance positions energy shifts δE142 150(2s-2p1/2) = 40.2(3)(6) meV [(stat)(sys)] and δE142 150(2s - 2p3/2) = 42.3(12)(20)meV of 2s - 2pj transitions were deduced. An evaluation of these values within a full QED treatment yields a change in the mean-square charge radius of 142 150δ⟨ r2⟩ = -1.36(1)(3) fm2. The approach is conceptually new and combines the advantage of a …
Triple-Differential Cross Sections For Target Ionization With Simultaneous Projectile Detachment In 200-Kev H⁻ + He Collisions, T. Ferger, Michael Schulz, Daniel Fischer, B. Najjari, R. Moshammer, J. D. Ullrich
Triple-Differential Cross Sections For Target Ionization With Simultaneous Projectile Detachment In 200-Kev H⁻ + He Collisions, T. Ferger, Michael Schulz, Daniel Fischer, B. Najjari, R. Moshammer, J. D. Ullrich
Physics Faculty Research & Creative Works
We have performed a kinematically complete experiment for target ionization with simultaneous projectile detachment (TIPD) in 200-keV H− + He collisions. From the data we extracted triple-differential cross sections (TDCSs) for each electron separately. These TDCSs closely resemble corresponding data for single ionization by charged-particle impact. Surprisingly, the contributions from higher-order processes to TIPD, proceeding through two independent interactions of each electron with the core of the respective other collision partner, are found to be somewhat larger than the first-order process proceeding through the electron-electron interaction.
Two-Loop Bethe Logarithms For Non- S Levels, Ulrich D. Jentschura
Two-Loop Bethe Logarithms For Non- S Levels, Ulrich D. Jentschura
Physics Faculty Research & Creative Works
Two-loop Bethe logarithms are calculated for excited P and D states in hydrogenlike systems, and estimates are presented for all states with higher angular momenta. These results complete our knowledge of the P and D energy levels in hydrogen at the order of α8 mec2, where me is the electron mass and c is the speed of light, and scale as Z6, where Z is the nuclear charge number. Our analytic and numerical calculations are consistent with the complete absence of logarithmic terms of order (απ)2 (Zα)6 ln [(Zα)-2] …
K Α₁ Radiation From Heavy, Heliumlike Ions Produced In Relativistic Collisions, Andrey S. Surzhykov, Ulrich D. Jentschura, Th H. Stohlker, Stephan Fritzsche
K Α₁ Radiation From Heavy, Heliumlike Ions Produced In Relativistic Collisions, Andrey S. Surzhykov, Ulrich D. Jentschura, Th H. Stohlker, Stephan Fritzsche
Physics Faculty Research & Creative Works
Bound-state transitions in few-electron, heavy ions following radiative electron capture are studied within the framework of the density matrix theory and the multiconfiguration Dirac-Fock approach. Special attention is paid to the K α1 (1 s1/2 2 p3/2 1.3PJ=1,2→1s21/2 1SJ=0) radiative decay of heliumlike uranium U90+ projectiles. This decay has recently been observed at the GSI facility in Darmstadt, giving rise to a surprisingly isotropic angular distribution, which is inconsistent with previous experiments and calculations based on a "one-particle" model. We show that the unexpected isotropy essentially results from …
Multiple Scattering Mechanisms In Simultaneous Projectile-Electron And Target-Electron Ejection In H⁻ + He Collisions, Michael Schulz, T. Ferger, Daniel Fischer, R. Moshammer, J. D. Ullrich
Multiple Scattering Mechanisms In Simultaneous Projectile-Electron And Target-Electron Ejection In H⁻ + He Collisions, Michael Schulz, T. Ferger, Daniel Fischer, R. Moshammer, J. D. Ullrich
Physics Faculty Research & Creative Works
We studied simultaneous electron ejection from both collision partners in 200-keV H-+He collisions in a kinematically complete experiment by measuring the fully momentum-analyzed recoil ions and both active electrons in coincidence. The data were analyzed in terms of Dalitz spectra, in which the momentum exchange between three particles is plotted simultaneously in a single spectrum. We found that the energy transfer occurs predominantly between the active electrons, but most of the momentum is exchanged in elastic scattering between the cores of the collision partners.
Hyperspherical Close-Coupling Calculations For Electron-Capture Cross Sections In Low-Energy Ne¹⁰⁺ +H (1s) Collisions, P. Barragan, Anh-Thu Le, C. D. Lin
Hyperspherical Close-Coupling Calculations For Electron-Capture Cross Sections In Low-Energy Ne¹⁰⁺ +H (1s) Collisions, P. Barragan, Anh-Thu Le, C. D. Lin
Physics Faculty Research & Creative Works
We present total and partial electron-capture cross sections for Ne¹⁰⁺ +H (1s) collisions at energies from 0.01 eV to 1 keV using the hyperspherical close-coupling method. Good agreements with the previous calculations by the classical-trajectory Monte-Carlo method are found for total capture cross section, but not for partial cross sections, especially below about 200 eV/amu. We found that the total cross section is mainly due to the population of n=7 channels and only at energies above 50 eV/amu n = 5,6 channels begin to contribute to the total cross section.
Polarization-Operator Approach To Electron-Positron Pair Production In Combined Laser And Coulomb Fields, A. I. Milstein, Carsten Muller, Karen Z. Hatsagortsyan, Ulrich D. Jentschura, Christoph H. Keitel
Polarization-Operator Approach To Electron-Positron Pair Production In Combined Laser And Coulomb Fields, A. I. Milstein, Carsten Muller, Karen Z. Hatsagortsyan, Ulrich D. Jentschura, Christoph H. Keitel
Physics Faculty Research & Creative Works
The optical theorem is applied to the process of electron-positron pair creation in the superposition of a nuclear Coulomb and a strong laser field. We derive representations for the total production rate as twofold integrals, both for circular laser polarization and for the general case of elliptic polarization. Our approach allows us to obtain, by analytical means, the asymptotic behavior of the pair creation rate for various limits of interest. In particular, we consider pair production by two-photon absorption and show that, close to the energetic threshold of this process, the rate obeys a power law in the laser frequency …
(E,2e) Measurements On Xenon: Reexamination Of The Fine-Structure Effect, Radmila Panajotovic, Julian C A Lower, Erich Weigold, A. Prideaux, Don H. Madison
(E,2e) Measurements On Xenon: Reexamination Of The Fine-Structure Effect, Radmila Panajotovic, Julian C A Lower, Erich Weigold, A. Prideaux, Don H. Madison
Physics Faculty Research & Creative Works
The process of electron scattering from heavy target atoms is of considerable interest due to the enhanced role of relativistic effects and distortion of the electron trajectories resulting from the large value of nuclear charge. Here we present (e,2e) ionization measurements and distorted-wave Born approximation calculations for the scattering of spin-polarized electrons from xenon atoms in which the fine-structure levels of the residual ion are resolved. Comparison of measurements performed using a high-sensitivity toroidal analyzer spectrometer with the predictions of sophisticated calculations provide an improved understanding of the ionization dynamics of heavy target atoms and the treatment of electron exchange …
Radiative Electron Capture Into High- Z Few-Electron Ions: Alignment Of The Excited Ionic States, Andrey S. Surzhykov, Ulrich D. Jentschura, Th H. Stohlker, Stephan Fritzsche
Radiative Electron Capture Into High- Z Few-Electron Ions: Alignment Of The Excited Ionic States, Andrey S. Surzhykov, Ulrich D. Jentschura, Th H. Stohlker, Stephan Fritzsche
Physics Faculty Research & Creative Works
We lay out a unified formalism for the description of radiative electron capture into excited states of heavy, few-electron ions and their subsequent decay, including a full account of many-electron effects and higher-order multipoles of the radiation field. In particular, the density-matrix theory is applied to explore the magnetic sublevel population of the residual ions, as described in terms of alignment parameters. For the electron capture into the initially hydrogenlike U91+ and lithiumlike U89+ uranium projectiles, the alignment parameters are calculated, within the multiconfiguration Dirac-Fock approach, as a function of the collision energy and for different ionic states. …
Mutual Ionization In 200-Kev H⁻+ He Collisions, T. Ferger, Daniel Fischer, Michael Schulz, R. Moshammer, A. B. Voitkiv, B. Najjari, J. Ullrich
Mutual Ionization In 200-Kev H⁻+ He Collisions, T. Ferger, Daniel Fischer, Michael Schulz, R. Moshammer, A. B. Voitkiv, B. Najjari, J. Ullrich
Physics Faculty Research & Creative Works
We studied mutual ionization in 200-keV H-+He collisions in a kinematically complete experiment by measuring the fully momentum-analyzed recoil ions and both active electrons in coincidence. Comparison of the data to our calculations, based on various theoretical models, show that mutual ionization proceeds predominantly through the interaction between both electrons. The post-collision interaction between the outgoing ejected electrons as well as higher order processes involving the interaction between the core of both collision partners are also important.
Comparison Of Hyperspherical Versus Common-Reaction-Coordinate Close-Coupling Methods For Ion-Atom Collisions At Low Energies, Anh-Thu Le, C. D. Lin, L. F. Errea, L. Mendez, A. Riera, B. Pons
Comparison Of Hyperspherical Versus Common-Reaction-Coordinate Close-Coupling Methods For Ion-Atom Collisions At Low Energies, Anh-Thu Le, C. D. Lin, L. F. Errea, L. Mendez, A. Riera, B. Pons
Physics Faculty Research & Creative Works
We present detailed comparisons between the two quantal approaches--hyperspherical close-coupling and common-reaction-coordinate close-coupling methods--on an exemplary case of He²⁺ + H(1s) collisions at center-of-mass energy from 20eV up to 1.6keV. It is shown that the partial-wave charge-transfer cross sections from the two approaches agree very well at low energy below 200eV down to 30eV. This good agreement is a strong indication of the validity of both methods. The small difference at very low energies and the convergence with respect to the number of channels in both approaches at higher energies are also discussed.
Probing Scattering Wave Functions Close To The Nucleus, Don H. Madison, Daniel Fischer, Matthew S. Foster, Michael Schulz, Robert Moshammer, Stephenie J. Jones, Joachim Hermann Ullrich
Probing Scattering Wave Functions Close To The Nucleus, Don H. Madison, Daniel Fischer, Matthew S. Foster, Michael Schulz, Robert Moshammer, Stephenie J. Jones, Joachim Hermann Ullrich
Physics Faculty Research & Creative Works
Recently, three-dimensional imaging of the ejected electrons following 100 MeV/amu C6+ single ionization of helium led to the observation of a new structure not predicted by theory [M. Schulz et al., Nature (London) 422, 48 (2003)]. Instead of the usual “recoil lobe” centered on the momentum-transfer axis, a ring-shaped structure centered on the beam axis was observed. New measurements at 2 MeV/amu exhibit a similar structure, which is now predicted by theory. We argue that the same theory failed at 100 MeV/amu because the faster projectiles probe distances much closer to the nucleus, where our multiple-scattering model is expected …
Role Of The Ground State In Electron-Atom Double Ionization, Stephenie J. Jones, Don H. Madison
Role Of The Ground State In Electron-Atom Double Ionization, Stephenie J. Jones, Don H. Madison
Physics Faculty Research & Creative Works
Recently, absolute measurements have been reported for double ionization of helium by 5.6 keV electron-impact. At this high energy, one would think that the first Born approximation for the interaction of the projectile with the atom would be valid. However, on the basis of a lowest-order implementation of a Faddeev-type approach, Berakdar concluded that the approximation was not valid. Here we argue that (i) it is valid at this energy and (ii) the previous discrepancy between calculations in the first Born approximation and the overall magnitude of the measurements was due to a poor description of the ground state.
Disorder-Induced Rounding Of Certain Quantum Phase Transitions, Thomas Vojta
Disorder-Induced Rounding Of Certain Quantum Phase Transitions, Thomas Vojta
Physics Faculty Research & Creative Works
We study the influence of quenched disorder on quantum phase transitions in systems with overdamped dynamics. For Ising order-parameter symmetry disorder destroys the sharp phase transition by rounding because a static order parameter can develop on rare spatial regions. This leads to an exponential dependence of the order parameter on the coupling constant. At finite temperatures the static order on the rare regions is destroyed. This restores the phase transition and leads to a double exponential relation between critical temperature and coupling strength. We discuss the behavior based on Lifshitz-tail arguments and illustrate the results by simulations of a model …
Perturbative And Nonperturbative Calculations Of Electron-Hydrogen Ionization, Stephenie J. Jones, Don H. Madison, Mark D. Baertschy
Perturbative And Nonperturbative Calculations Of Electron-Hydrogen Ionization, Stephenie J. Jones, Don H. Madison, Mark D. Baertschy
Physics Faculty Research & Creative Works
We compare calculations of the fully differential cross section for ionization of atomic hydrogen by electron impact using two different theories-the perturbative CDW-EIS (continuum distorted wave with eikonal initial state) approximation and the nonperturbative ECS (exterior complex scaling) method. For this comparison, we chose an impact energy of 54.4 eV, since this is near the lowest energy that our perturbative approach would be applicable and near the highest energy that can be tackled by the ECS method with our present computational resources. For the case of equal-energy outgoing electrons investigated here, the two theories predict nearly identical results except that …
Slow Convergence Of The Born Approximation For Electron-Atom Ionization, Stephenie J. Jones, Don H. Madison
Slow Convergence Of The Born Approximation For Electron-Atom Ionization, Stephenie J. Jones, Don H. Madison
Physics Faculty Research & Creative Works
It is usually assumed that the first-Born approximation for electron-atom ionization becomes valid for the fully differential cross section at sufficiently high impact energies, at least for asymmetric collisions where the projectile suffers only a small energy loss and is scattered by a small angle. Here we investigate this assumption quantitatively for ionization of hydrogen atoms. We find that convergence of the Born approximation to the correct nonrelativistic result is generally achieved only at energies where relativistic effects start to become important. Consequently, the assumption that the Born approximation becomes valid for high energy is inaccurate, since by the time …