Bulletin of the American Physical Society
69th Annual Gaseous Electronics Conference
Volume 61, Number 9
Monday–Friday, October 10–14, 2016; Bochum, Germany
Session JW1: Antimatter Collisions and Ionization ProcessesFocus
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Chair: Allan Stauffer, York University Room: 1 |
Wednesday, October 12, 2016 8:30AM - 9:00AM |
JW1.00001: Collisions involving Antimatter Invited Speaker: Gaetana Laricchia Much progress in the understanding of the interactions between the matter and antimatter has been achieved through studies of collisions of positrons and positronium (Ps, the short-lived atom made of an electron and a positron) with atoms and molecules. In this talk, the focus will be on recent experiments performed at UCL concerning positronium formation [e.g. 1-3] and its scattering [e.g. 4-6]. Studies have now progressed to an exciting new phase. The finding of a similarity between the scattering probabilities of positronium and equivelocity electrons [5] has guided towards the observation of positronium resonant scattering [6] and the development of a positronium beam at incident energies below its break-up threshold [4], allowing searches in an energy regime which, for electrons, is rich in subtle quantum mechanical effects, including "target transparency" [4].~ Possible avenues of future exploration will be indicated.\\ \\References: 1.M. Shipman, S. Armitage, J. Beale, S. J. Brawley, S. E. Fayer, A. J. Garner, D. E. Leslie, P. Van Reeth, G. Laricchia,~\textit{Phys. Rev. Letts.~}115, (2015) 033401\newline 2.D. A. Cooke, D. J. Murtagh, G. Laricchia~\textit{Phys. Rev. Letts.~}104 (2010) 073201\newline 3.D.J. Murtagh, D.A. Cooke, G. Laricchia~\textit{Phys. Rev. Letts.~~}102 (2009) 133202\newline 4.S.J. Brawley, S.E. Fayer, M. Shipman, G. Laricchia (2015)~\textit{Phys. Rev. Letts.~}115 (2015) 223201\newline 5.S. J. Brawley, S. Armitage, J. Beale, D. E. Leslie, A. I. Williams, G. Laricchia~\textit{Science~}330 (2010) 789\newline 6.S. J. Brawley, A. I. Williams, M. Shipman, G. Laricchia~\textit{Phys. Rev. Letts.~}105 (2010) 263401 [Preview Abstract] |
Wednesday, October 12, 2016 9:00AM - 9:15AM |
JW1.00002: Stationary wave-packet continuum-discretization approach to differential ionization in antiproton-hydrogen collisions Ilkhom Abdurakhmanov, Alisher Kadyrov, Igor Bray A novel single-center close-coupling approach to differential ionization in antiproton-hydrogen collisions has been developed. The continuous spectrum of the target has been discretized using stationary wave packets constructed from the Coulomb wave functions, the eigenstates of the target Hamiltonian. Such continuum discretization allows one to generate pseudostates with arbitrary energies and distribution which is ideal for detailed differential ionization studies. A comprehensive set of benchmark results from integrated to fully differential cross sections for antiproton-impact ionization of hydrogen in a wide energy range is provided. Contrary to previous predictions, we find that at low incident energies the singly differential cross section has a maximum away from zero emission energy. This feature could not be seen without a fine discretization of the low-energy part of the continuum. The ability of the proposed approach to generate target states with arbitrary energies and distribution is ideal for studies of ion-atom collisions where two-center rearrangement processes take place. Studies of those systems in the most detailed fully differential level will shed a light on the issues of double-counting of the continuum associated with the two-center expansion basis. [Preview Abstract] |
Wednesday, October 12, 2016 9:15AM - 9:45AM |
JW1.00003: A Sturmian approach for ionization processes of atoms and molecules Invited Speaker: Lorenzo Ugo Ancarani The Sturmian approach, using Generalized Sturmian Functions (GSF), is a spectral method that has been applied successfully both for structure calculations [1] and for the study of several ionization processes [2] with atomic targets. GSF are two-body functions that solve a Sturm-Liouville problem. They can be used as a basis set to deal with two- or three-body bound or scattering problems. By construction, the whole GSF set can be chosen to possess asymptotic conditions appropriate for the physical problem under consideration: bound-type behavior with a specific asymptotic charge are chosen for bound states, while -- for example - outgoing behavior with a given adequate energy are taken for solving scattering processes. This important intrinsic property makes GSF basis sets - and thus the whole approach - computationally efficient. In the case of ionization, a specific feature of our methodology is that the scattering amplitude and the corresponding cross section are extracted directly from the asymptotic part of the scattering function without requiring the evaluation of a matrix element. Compared to the case of many-electron atoms several extra challenges occur for molecules: the scattering problem is generally multicenter and highly non-central, and the molecular orientation must also be taken into account. These features make the computational task much more cumbersome and expensive than for atomic targets. The Sturmian approach with GSF has been recently extended and implemented to study single ionization of small polyatomic molecules by photon and electron impact [3]. Results for a variety of single and double ionization processes will be presented. [1] G. Gasaneo et al., Adv. Quantum Chem. \textbf{67,} 153 (2013). [2] M.J. Ambrosio et al., J Phys. B \textbf{48} 055204 (2015)~; J.M. Randazzo et al., Eur. J. Phys. D, \textbf{69}, 189 (2015)~; M.J. Ambrosio et al., Phys. Rev. A, \textbf{92}, 042704 (2015) [3] C.M. Granados-Castro et al., Adv. Quantum Chem., \textbf{73}, 3 (2016); C.M. Granados-Castro, PhD Thesis -- Universit\'{e} de Lorraine (2016). [Preview Abstract] |
Wednesday, October 12, 2016 9:45AM - 10:00AM |
JW1.00004: Fluctuation capture in dense gases and liquids - trapping, detrapping and non-equilibrium transport Daniel Cocks, Ron White When charged particles travel through a background of a dense gas or liquid the correlations in the fluid significantly modify the transport of the charged particle. In particular, a new process becomes available, in which the particle is captured into a local fluctuation (bubble or cluster) of the fluid. The trapping has an influence on all transport coefficients, especially annihilation rates of positrons and positronium. Understanding fluctuation capture is important in medical diagnostics, therapy and particle detectors in the low-energy regime, but has so far been unable to be accounted for in transport simulations. We present a new framework that produces energy-resolved ``capture cross sections'' $\sigma_{\mathrm{cap}}(\epsilon)$ along with ``waiting time distributions'' $\Theta(t)$ which allow transport theories to include capture as a process. We demonstrate good agreement between our ab initio calculations and experimental measurements of electrons and positrons in dense noble-gas fluids. [Preview Abstract] |
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