https://doi.org/10.1140/epjs/s11734-026-02259-1
Regular Article
Cusp-electron production in collisions of mixed-state Be-like oxygen beams with helium targets
1
Department of Physics, University of Crete, 70013, Heraklion, Greece
2
Tandem Accelerator Laboratory, Institute of Nuclear and Particle Physics, NCSR “Demokritos”, 15310, Aghia Paraskevi, Greece
3
Institut für Kernphysik, J. W. Goethe-Universität Frankfurt am Main, 60438, Frankfurt am Main, Germany
4
Department of Physics, University of Ioannina, 45110, Ioannina, Greece
5
Institut des Nanosciences de Paris, Sorbonne Université, CNRS, Campus Pierre et
Marie Curie, 75005, Paris, France
a
This email address is being protected from spambots. You need JavaScript enabled to view it.
Received:
29
December
2025
Accepted:
3
March
2026
Published online:
17
March
2026
Abstract
We report on double differential cross section (DDCS) measurements of cusp electrons emitted at zero degrees in swift collisions of mixed-state O
ions with He gas targets. The content of the mixed-state beam is varied depending on the upcharging method, i.e. gas or foil stripping, and thus the DDCS spectra bear the signature of the contribution of both components of the mixed-state beam. Additionally, high resolution Auger spectra corresponding to different beam content were recorded allowing thus for the determination of the fraction of the 
part of the beam. Our DDCS measurements, involving four projectile electrons in open-shell configuration, provide stringent tests for current advanced collision theories such as the continuum distorted wave theories.
Present address: Institut des Nanosciences de Paris, Sorbonne Université, CNRS, Campus Pierre et Marie Curie, 75005, Paris, France
© The Author(s) 2026
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
