Kinematically complete experimental study of Compton scattering at helium atoms near the threshold

• DOI: 10.1038/s41567-020-0880-2
• Publication Date: 2020-04-13T16:02:48Z
• Authors: Max Kircher; Florian Trinter; Sven Grundmann; Isabel Vela-Perez; Simon Brennecke; Nicolas Eicke; Jonas Rist; Sebastian Eckart; Salim Houamer; Ochbadrakh Chuluu...; Yuri V. Popov; Igor P. Volobuev; Kai Bagschik; M. Novella Pianca...; Manfred Lein; Till Jahnke; Markus S. Schöffler; Reinhard Dörner
• Keywords: Cold target recoil ion momentum spectroscopies; Momentum; Atomic Physics (physics.atom-ph); FOS: Physical sciences; Electrons; Neutron scattering; Interaction process; Binding energy; Helium; 530; 01 natural sciences; Ion bombardment; Physics - Atomic Physics; Momentum correlation; Electron impact-ionization; Impact ionization; 0103 physical sciences; Complete experiment; Momentum transfer; info:eu-repo/classification/ddc/530; Ions; Photons; Ultrashort optical pulse; Quasi-free electron; Ion-impact ionization; Compton scattering

Compton scattering is one of the fundamental interaction processes of light with matter. When discovered, it was described as a billiard-type collision of a photon ‘kicking’ a quasi-free electron. With decreasing photon energy, the maximum possible momentum transfer becomes so small that the corresponding energy falls below the binding energy of the electron. In this regime, ionization by Compton scattering becomes an intriguing quantum phenomenon. Here, we report on a kinematically complete experiment studying Compton scattering off helium atoms in that regime. We determine the momentum correlations of the electron, the recoiling ion and the scattered photon in a coincidence experiment based on cold target recoil ion momentum spectroscopy, finding that electrons are not only emitted in the direction of the momentum transfer, but that there is a second peak of ejection to the backward direction. This finding links Compton scattering to processes such as ionization by ultrashort optical pulses, electron impact ionization, ion impact ionization and neutron scattering, where similar momentum patterns occur.<br/>Nature physics 16(7), 756 - 760 (2020). doi:10.1038/s41567-020-0880-2<br/>Published by Nature Publishing Group, Basingstoke<br/>