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Absolute Differential Positronium-Formation Cross Sections.

M Shipman1, S Armitage1, J Beale1

  • 1UCL Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom.

Physical Review Letters
|August 1, 2015
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Summary
This summary is machine-generated.

This study presents the first experimental measurements of differential cross sections for ground-state positronium formation in He, Ar, H2, and CO2. Results show a higher tendency for forward emission of positronium from Helium and Hydrogen molecules.

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Area of Science:

  • Atomic and Molecular Physics
  • Quantum Chemistry
  • Positron Scattering

Background:

  • Positronium (Ps) formation is a key process in positron-atom/molecule collisions.
  • Understanding Ps formation cross sections is crucial for various applications, including materials science and fundamental physics.
  • Previous experimental data for differential cross sections near 0° were limited.

Purpose of the Study:

  • To provide the first absolute experimental determination of differential cross sections for ground-state positronium formation.
  • To investigate the angular distribution of positronium formation for various targets (He, Ar, H2, CO2).
  • To compare experimental results with theoretical predictions and analyze target-specific emission propensities.

Main Methods:

  • Absolute measurements of differential cross sections using a high-resolution positron beam.
  • Scattering experiments conducted at low angles (near 0°) to probe forward emission.
  • Analysis of the ratio between differential and integrated cross sections.

Main Results:

  • First absolute experimental differential cross sections for ground-state positronium formation are reported for He, Ar, H2, and CO2.
  • Experimental data are compared with existing theoretical models.
  • A higher propensity for forward emission of positronium was observed for Helium and Hydrogen molecule targets compared to Argon and Carbon Dioxide.

Conclusions:

  • The experimental data provide a benchmark for theoretical calculations of positronium formation.
  • The observed forward scattering asymmetry highlights target-specific effects in the positronium formation mechanism.
  • Further theoretical and experimental investigations are warranted to fully understand the nuances of positronium formation dynamics.