Observation of a shape resonance of the positronium negative ion

Koji Michishio (), Tsuneto Kanai, Susumu Kuma, Toshiyuki Azuma, Ken Wada, Izumi Mochizuki, Toshio Hyodo, Akira Yagishita and Yasuyuki Nagashima
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Koji Michishio: Tokyo University of Science
Tsuneto Kanai: Atomic, Molecular and Optical Physics Laboratory
Susumu Kuma: Atomic, Molecular and Optical Physics Laboratory
Toshiyuki Azuma: Atomic, Molecular and Optical Physics Laboratory
Ken Wada: Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK)
Izumi Mochizuki: Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK)
Toshio Hyodo: Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK)
Akira Yagishita: Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK)
Yasuyuki Nagashima: Tokyo University of Science

Nature Communications, 2016, vol. 7, issue 1, 1-5

Abstract: 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.

Date: 2016
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DOI: 10.1038/ncomms11060

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