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Michishio K, Kuma S, Nagata Y, Chiari L, Iizuka T, Mikami R, Azuma T, Nagashima Y. Threshold Photodetachment Spectroscopy of the Positronium Negative Ion. PHYSICAL REVIEW LETTERS 2020; 125:063001. [PMID: 32845653 DOI: 10.1103/physrevlett.125.063001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2020] [Accepted: 07/09/2020] [Indexed: 06/11/2023]
Abstract
Threshold photodetachment spectroscopy of the positronium negative ion has been accomplished for the first time employing an efficient source of the ions and photodetachment techniques combined with a tunable optical parametric oscillator and amplifier laser. The photodetachment threshold, corresponding to the electron affinity of positronium (1^{3}S_{1}), was determined to be 326.88±0.09(stat)±0.10(syst) meV by laser photodetachment threshold measurements. This result is consistent with a variational calculation corrected for leading relativistic and quantum electrodynamical effects.
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Affiliation(s)
- Koji Michishio
- National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
- Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan
| | - Susumu Kuma
- Atomic, Molecular and Optical Physics Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Yugo Nagata
- Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan
| | - Luca Chiari
- Department of Applied Chemistry and Biotechnology, Faculty of Engineering, Chiba University, 1-33 Yayoi, Inage, Chiba 263-8522, Japan
| | - Taro Iizuka
- Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan
| | - Riki Mikami
- Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan
| | - Toshiyuki Azuma
- Atomic, Molecular and Optical Physics Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Yasuyuki Nagashima
- Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan
- Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
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A Note on the Opacity of the Sun’s Atmosphere. ATOMS 2020. [DOI: 10.3390/atoms8030037] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The opacity of the atmosphere of the Sun is due to processes such as Thomson scattering, bound–bound transitions and photodetachment (bound–free) of hydrogen and positronium ions. The well-studied free–free transitions involving photons, electrons, and hydrogen atoms are re-examined, while free–free transitions involving positrons are considered for the first time. Cross sections, averaged over a Maxwellian velocity distribution, involving positrons are comparable to those involving electrons. This indicates that positrons do contribute to the opacity of the atmosphere of the Sun. Accurate results are obtained because definitive phase shifts are known for electron–hydrogen and positron–hydrogen scattering.
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Calculations of Resonance Parameters for the Doubly Excited 1P° States in Ps− Using Exponentially Correlated Wave Functions. ATOMS 2019. [DOI: 10.3390/atoms8010001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Recent observations on resonance states of the positronium negative ion (Ps−) in the laboratory created huge interest in terms of the calculation of the resonance parameters of the simple three-lepton system. We calculate the resonance parameters for the doubly excited 1P° states in Ps− using correlated exponential wave functions based on the complex-coordinate rotation method. The resonance energies and widths for the 1P° Feshbach resonance states in Ps− below the N = 2, 3, 4, 5 Ps thresholds are reported. The 1P° shape resonance above the N = 2, 4 Ps thresholds are also reported. Our predications are in agreement with the available results. Few Feshbach resonance parameters below the N = 4 and 5 Ps thresholds have been reported in the literature. Our predictions will provide useful information for future resonance experiments in Ps−.
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Michishio K, Chiari L, Tanaka F, Oshima N, Nagashima Y. A high-quality and energy-tunable positronium beam system employing a trap-based positron beam. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2019; 90:023305. [PMID: 30831693 DOI: 10.1063/1.5060619] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2018] [Accepted: 01/17/2019] [Indexed: 06/09/2023]
Abstract
We constructed a new apparatus, built upon a trap-based slow positron beam, for the production of a collimated, energy-tunable positronium beam under ultra-high vacuum conditions employing the photodetachment of positronium negative ions. A slow positron generator consisting of a 22Na radioisotope (20 mCi) combined with a buffer-gas positron trap is employed to generate high-quality, nano-second positron bursts with a repetition rate of 1 Hz-1 kHz. The positron bursts are focused onto an efficient positron-to-positronium negative ion converter, a Na-coated W thin film in a transmission geometry, using a magnetic lens system. The ions emitted from the opposite surface of the film are electrostatically accelerated to a given energy and photodetached by a pulsed infrared laser to form a mono-energetic positronium beam with kinetic energies of 0.2 keV-3.3 keV. The achieved detection rate of Ps atoms is 23 cps at the energy of 3.3 keV with a signal-to-background ratio as high as 300. The energy spread of the beam was evaluated by comparing the result of the time-of-flight measurements and particle-tracking simulations. With the use of a collimator of 1 mm diameter, a coherent beam with an angular divergence of less than 0.3° is obtained. The obtained Ps beam, having a much higher quality than those reported hitherto, will open up a new field of experimental investigations, such as Ps interacting with a variety of materials and fundamental studies on Ps spectroscopy.
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Affiliation(s)
- K Michishio
- Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan
| | - L Chiari
- Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan
| | - F Tanaka
- Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan
| | - N Oshima
- National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
| | - Y Nagashima
- Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan
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Abstract
Lyman-α radiation ( 2 P → 1 S ) has been seen from astrophysical sources and the sun. The line shape of this transition has been measured recently in Ps atoms both inside and outside a porous silica target. In the photodetachment of Ps−, the residual Ps atom can be left in the 2P state instead of the 1S state giving rise to positronium Lyman radiation at 2432 A0. Photodetachment cross sections of Ps− have been calculated when the Ps atom is left in nP states, n being 2, 3, 4, 5, 6 and 7, using the asymptotic form of the bound-state wave function and a plane wave for the final state wave function, following the approach of Ohmura and Ohmura [Phys. Rev. 1960, 118, 154] in the photodetachment of H−.
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Suzuki Y, Hagiwara S, Watanabe K. Time-Dependent Multicomponent Density Functional Theory for Coupled Electron-Positron Dynamics. PHYSICAL REVIEW LETTERS 2018; 121:133001. [PMID: 30312034 DOI: 10.1103/physrevlett.121.133001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2018] [Indexed: 06/08/2023]
Abstract
Electron-positron interactions have been utilized in various fields of science. Here we develop time-dependent multicomponent density functional theory to study the coupled electron-positron dynamics from first principles. We prove that there are coupled time-dependent single-particle equations that can provide the electron and positron density dynamics, and derive the formally exact expression for their effective potentials. Introducing the adiabatic local density approximation to time-dependent electron-positron correlation, we apply the theory to the dynamics of a positronic lithium hydride molecule under a laser field. We demonstrate the significance of the coupling between electronic and positronic motion by revealing the complex positron detachment mechanism and the suppression of electronic resonant excitation by the screening effect of the positron.
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Affiliation(s)
- Yasumitsu Suzuki
- Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
| | - Satoshi Hagiwara
- Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
| | - Kazuyuki Watanabe
- Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
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Observation of a shape resonance of the positronium negative ion. Nat Commun 2016; 7:11060. [PMID: 26983496 PMCID: PMC4800431 DOI: 10.1038/ncomms11060] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Accepted: 02/16/2016] [Indexed: 12/05/2022] Open
Abstract
When an electron binds to its anti-matter counterpart, the positron, it forms the exotic atom positronium (Ps). Ps can further bind to another electron to form the positronium negative ion, Ps− (e−e+e−). Since its constituents are solely point-like particles with the same mass, this system provides an excellent testing ground for the three-body problem in quantum mechanics. While theoretical works on its energy level and dynamics have been performed extensively, experimental investigations of its characteristics have been hampered by the weak ion yield and short annihilation lifetime. Here we report on the laser spectroscopy study of Ps−, using a source of efficiently produced ions, generated from the bombardment of slow positrons onto a Na-coated W surface. A strong shape resonance of 1Po symmetry has been observed near the Ps (n=2) formation threshold. The resonance energy and width measured are in good agreement with the result of three-body calculations. The Positronium negative ion is formed by two electrons bound to a positron, and experimental investigations of its states and energy levels are difficult due to its short lifetime. Here, the authors report on laser spectroscopy of positronium using a source of efficiently produced ions.
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Cooper BS, Alonso AM, Deller A, Wall TE, Cassidy DB. A trap-based pulsed positron beam optimised for positronium laser spectroscopy. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2015; 86:103101. [PMID: 26520934 DOI: 10.1063/1.4931690] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We describe a pulsed positron beam that is optimised for positronium (Ps) laser-spectroscopy experiments. The system is based on a two-stage Surko-type buffer gas trap that produces 4 ns wide pulses containing up to 5 × 10(5) positrons at a rate of 0.5-10 Hz. By implanting positrons from the trap into a suitable target material, a dilute positronium gas with an initial density of the order of 10(7) cm(-3) is created in vacuum. This is then probed with pulsed (ns) laser systems, where various Ps-laser interactions have been observed via changes in Ps annihilation rates using a fast gamma ray detector. We demonstrate the capabilities of the apparatus and detection methodology via the observation of Rydberg positronium atoms with principal quantum numbers ranging from 11 to 22 and the Stark broadening of the n = 2 → 11 transition in electric fields.
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Affiliation(s)
- B S Cooper
- Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - A M Alonso
- Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - A Deller
- Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - T E Wall
- Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - D B Cassidy
- Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom
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Zhou Y, Mao W, Li Q, Wang J, He C. Formation and annihilation of positronium in silica aerogels under atmosphere of oxygen and nitrogen mixture. Chem Phys 2015. [DOI: 10.1016/j.chemphys.2015.07.030] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Frolov AM. Annihilation, bound state properties and photodetachment of the positronium negatively charged ion. Chem Phys Lett 2015. [DOI: 10.1016/j.cplett.2015.02.044] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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11
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12
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Wada K, Hyodo T, Kosuge T, Saito Y, Ikeda M, Ohsawa S, Shidara T, Michishio K, Tachibana T, Terabe H, Suzuki RH, Nagashima Y, Fukaya Y, Maekawa M, Mochizuki I, Kawasuso A. New experiment stations at KEK Slow Positron Facility. ACTA ACUST UNITED AC 2013. [DOI: 10.1088/1742-6596/443/1/012082] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Cassidy DB, Hisakado TH, Tom HWK, Mills AP. Optical spectroscopy of molecular positronium. PHYSICAL REVIEW LETTERS 2012; 108:133402. [PMID: 22540698 DOI: 10.1103/physrevlett.108.133402] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2012] [Indexed: 05/31/2023]
Abstract
We report optical spectroscopic measurements of molecular positronium (Ps(2)), performed via a previously unobserved L=1 excited state. Ps(2) molecules created in a porous silica film, and also in vacuum from an Al(111) crystal, were resonantly excited and then photoionized by pulsed lasers, providing conclusive evidence for the production of this molecular matter-antimatter system and its excited state. Future experiments making use of the photoionized vacuum L=1 Ps(2) could provide a source of Ps(+) ions, as well as other multipositronic systems, such as Ps(2)H(-) or Ps(2)O.
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Affiliation(s)
- D B Cassidy
- Department of Physics and Astronomy, University of California, Riverside, California 92521-0413, USA
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Cassidy DB, Hisakado TH, Tom HWK, Mills AP. Efficient production of Rydberg positronium. PHYSICAL REVIEW LETTERS 2012; 108:043401. [PMID: 22400840 DOI: 10.1103/physrevlett.108.043401] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2011] [Indexed: 05/31/2023]
Abstract
We demonstrate experimentally the production of Rydberg positronium (Ps) atoms in a two-step process, comprising incoherent laser excitation, first to the 2(3)P state and then to states with principal quantum numbers ranging from 10 to 25. We find that excitation of 2(3)P atoms to Rydberg levels occurs very efficiently (~90%) and that the ~25% overall efficiency of the production of Rydberg atoms is determined almost entirely by the spectral overlap of the primary excitation laser and the Doppler broadened width of the 1 (3)S-2(3)P transition. The observed efficiency of Rydberg Ps production can be explained if stimulated emission back to the 2P states is suppressed, for example, by intermixing of the Rydberg state Stark sublevels. The efficient production of long-lived Rydberg Ps in a high magnetic field may make it possible to perform direct measurements of the gravitational free fall of Ps.
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Affiliation(s)
- D B Cassidy
- Department of Physics and Astronomy, University of California, Riverside, California 92521-0413, USA
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Cassidy DB, Hisakado TH, Tom HWK, Mills AP. Laser excitation of positronium in the Paschen-Back regime. PHYSICAL REVIEW LETTERS 2011; 106:173401. [PMID: 21635035 DOI: 10.1103/physrevlett.106.173401] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2011] [Indexed: 05/30/2023]
Abstract
Zeeman mixing of singlet and triplet 2P states of positronium (Ps) atoms, followed by decay back to the ground state, can effectively turn a long-lived triplet atom into a short-lived singlet state, which would seem to preclude laser cooling of Ps in a magnetic field. Here we report experiments which show that, in fact, because of the large splitting of the n=2 states in a high magnetic field (the Paschen-Back regime), the amount of such mixing diminishes approximately exponentially with an increasing magnetic field >0.01 T and is essentially eliminated above ∼2 T. Thus, laser cooling of Ps should be feasible at high fields, which will facilitate the production of a Ps Bose-Einstein condensate.
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Affiliation(s)
- D B Cassidy
- Department of Physics and Astronomy, University of California, Riverside, California 92521-0413, USA
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