| 1. |
- Froelich, Piotr, et al.
(author)
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Four-body treatment of the antihydrogen-positronium system : binding, structure, resonant states and collisions
- 2019
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In: Hyperfine Interactions. - : Springer. - 0304-3843 .- 1572-9540.
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Conference paper (peer-reviewed)abstract
- We have developed a coupled-rearrangement-channel method allowing the rigorous non-adiabatic treatment of the multi-channel scattering problem for four particles. We present the study of the binding, resonant and collisional properties of the (H) over bar -Ps system with the total angular momentum J = 0(+) (singlet positronic configuration). The binding energy, the life-times of the resonant states and the collisional cross sections are calculated and discussed. We present the preliminary cross sections for the elastic and inelastic (H) over bar -Ps scattering, notably for the excitation of Ps and for the rearrangement reaction producing the (H) over bar (+) ions.
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| 2. |
- Stegeby, Henrik, 1979-, et al.
(author)
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Two-Body Hadronic Densities From The Four-Body Wave Functions For The Hydrogen-Antihydrogen System
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Other publication (other academic/artistic)abstract
- The quantum-mechanical four-body problem for the hydrogen-antihydrogen system has beensolved by means of the variational implementation of the coupled-arrangement channel method.The wave functions have been formed using the Gaussian expansion method (GEM) in Jacobi co-ordinates; they explicitly include components corresponding to the rearrangement from hydrogen and antihydrogen (H + H') into Protonium and Positronium (Pn + Ps). We analyse the solutionsbelonging to the discretized spectrum of the 4-body eigenvalue problem at energies correspondingto the low energy H { Hcollisions. Two-body nuclear correlation functions are calculated from thefour-body wave functions, as to investigate the proton-antiproton motion in the region of rearrangement from H+H' to Pn+Ps. We monitor the adiabatic versus nonadiabatic behavior of the system asa function of internuclear separation and nd that outside the rearrangement region the adiabaticdescription is quite adequate. The nonadiabatic behavior signicantly in uences the nuclear motionin the rearrangement region and reduces the rate of proton-antiproton annihilation in low-energy hydrogen-antihydrogen collisions.
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| 3. |
- Yamashita, Takuma, et al.
(author)
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A coupled rearrangemnet channel analysis of positronium antihydride PsH
- 2017
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In: Journal of Physics, Conference Series. - : Institute of Physics (IOP). - 1742-6588 .- 1742-6596. ; 875
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Journal article (peer-reviewed)abstract
- Ground and resonance states of PsH are calculated with a coupled rearrangement-channel, four-body calculation. The structures of these states are examined with help of correlation functions and probabilities of finding two-body states in the total wavefunction. Asymptotic configurations of the ground and resonance states are determined from the tail behaviour of the correlation functions.
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| 4. |
- Yamashita, Takuma, et al.
(author)
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Bound and resonance states of positronic copper atoms
- 2017
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In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 50:20
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Journal article (peer-reviewed)abstract
- We report a theoretical calculation for the bound and S-wave resonance states of the positronic copper atom (e(+) Cu). A positron is a positively charged particle; therefore, a positronic atom has an attractive correlation between the positron and electron. A Gaussian expansion method is adopted to directly describe this correlation as well as the strong repulsive interaction with the nucleus. The correlation between the positron and electron is much more important than that between electrons in an analogous system of Cu-, although the formation of a positronium (Ps) in e(+) Cu is not expressed in the ground state structure explicitly. Resonance states are calculated with a complex scaling method and identified above the first excited state of the copper atom. Resonance states below Ps (n = 2) + Cu+ classified to a dipole series show agreement with a simple analytical law. Comparison of the resonance energies and widths of e(+) Cu with those of e(+) K, of which the potential energy of the host atom resembles that of e(+) Cu, reveals that the positions of the resonance for the e(+) Cu dipole series deviate equally from those of e(+) K.
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| 5. |
- Yamashita, Takuma, et al.
(author)
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Four-body Calculation of Inelastic Scattering Cross Sections of Positronium-Antihydrogen Collision
- 2021
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In: Few-body systems. - : Springer Science and Business Media LLC. - 0177-7963 .- 1432-5411. ; 62:4
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Journal article (peer-reviewed)abstract
- We overview our recent calculations of scattering cross sections of positronium–antihydrogen collisions. We discuss the cross sections calculated in the vicinity of the four-body resonances of H¯Ps and above the energy threshold for the formation of the antihydrogen positive ions (H¯+). In the former energy region where a Rydberg series of resonances dominated by the H¯+-e− interaction appears, we show a good agreement between the resonant profiles in the cross sections and the resonance energies calculated by the complex coordinate rotation method. H¯+ production cross sections near the threshold energy are reported for the positronium being initially in the (n, l) states with n≤3, together with all competing elastic/inelastic cross sections. Comparison of our results with the latest continuum distorted wave final state calculation is presented. A qualitative discrepancy concerning the dependence of cross sections on the angular momentum of Ps is indicated.
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| 6. |
- Yamashita, Takuma, et al.
(author)
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Near-threshold behavior of positronium-antihydrogen scattering cross sections
- 2022
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In: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society. - 2469-9926 .- 2469-9934. ; 105:5
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Journal article (peer-reviewed)abstract
- We have performed a comprehensive numerical investigation of the scattering of antihydrogen (H¯) and positronium (Ps) atoms, at collision energies just above the threshold for the rearrangement reaction resultingin H¯ + ions. Formation of H¯ + in H¯ + Ps collisions is of vivid interest for experiments with H¯ at CERN. We treat all open channels below the threshold for the rearrangement into H¯ + Ps (which includes elastic scattering, excitation and deexcitation of positronium to and from the excited states with n = 2, 3, polarization and depolarization of Ps(n, l), rearrangement into H¯ + + e−, and formation of Ps and H¯ in the reverse reaction). Our method is a combination of the variational calculation with the coupled rearrangement channel method. The four-body solutions of the Schrödinger equation, obtained via diagonalization of the full Hamiltonian, are combined with the channel functions that satisfy the correct asymptotic boundary conditions, in a procedure that delivers the scattering matrix S. The complete set of S-matrix elements for all allowed scattering processes is calculated (both in forward and reverse directions, without assumption of the detailed balance). The scattering cross sections are obtained from the S-matrix elements calculated for the total angular momenta J = 0–6, and for the positronic spin S = 0, required for the formation of H¯ +. The numerical accuracy of the calculation is checked using the criterion of unitarity of the S matrix. Convergence of the cross section is examined with respect to the partial wave contributions, under the constraint of conservation of total angular momentum and parity. We show that the energy behavior of the cross sections near thresholds is consistent with the Wigner laws. The cross sections for processes that compete with H¯ + formation are presented.
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| 7. |
- Yamashita, Takuma, et al.
(author)
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Near-threshold production of antihydrogen positive ion in positronium-antihydrogen collision
- 2021
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In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 23:1
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Journal article (peer-reviewed)abstract
- Near-threshold production of antihydrogen ion (H+) in positronium-antihydrogen collisions is predicted by a rigorous four-body scattering calculation. The convergence of the cross sections for the rearrangement and for all competing reactions (elastic scattering, de/excitation and de/polarization of positronium) is carefully examined against partial waves. The multi-channel scattering solutions are composed of functions that diagonalize the four-body Hamiltonian, and scattering functions that satisfy the correct asymptotic boundary conditions. The production rates of H+ show large discrepancies compared to more approximate calculations.
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