https://doi.org/10.1140/epja/s10050-023-00930-y
Special Article – New Tools and Techniques
Muonic atom spectroscopy with microgram target material
1
Institute of Nuclear Physics, Polish Academy of Sciences, Krakow, Poland
2
Paul Scherrer Institut, Villigen, Switzerland
3
Institut für Teilchen- und Astrophysik, ETH Zürich, Zürich, Switzerland
4
Institute of Nuclear Physics, Johannes Gutenberg University Mainz, Mainz, Germany
5
PRISMA+ Cluster of Excellence, Johannes Gutenberg University Mainz, Mainz, Germany
6
Instituut voor Kern- en Stralingfysica, KU Leuven, Leuven, Belgium
7
Department of Chemistry-TRIGA Site, Johannes Gutenberg University Mainz, Mainz, Germany
8
GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany
9
Helmholtz Institute Mainz, Mainz, Germany
10
Institut für Kernphysik, Universität zu Köln, Köln, Germany
11
Laboratoire Kastler Brossel, Sorbonne Université, CNRS, ENS-PSL Research University, Collège de France, Case 74; 4, place Jussieu, 75005, Paris, France
12
Institute of Physics, Johannes Gutenberg Universität Mainz, Mainz, Germany
13
Department of Physics, Universitá di Pisa, Pisa, Italy
14
Université Grenoble Alpes, CNRS, Grenoble INP, LPSC-IN2P3, 38026, Grenoble, France
Received:
28
September
2022
Accepted:
25
January
2023
Published online:
3
February
2023
Muonic atom spectroscopy–the measurement of the x rays emitted during the formation process of a muonic atom–has a long standing history in probing the shape and size of nuclei. In fact, almost all stable elements have been subject to muonic atom spectroscopy measurements and the absolute charge radii extracted from these measurements typically offer the highest accuracy available. However, so far only targets of at least a few hundred milligram could be used as it required to stop a muon beam directly in the target to form the muonic atom. We have developed a new method relying on repeated transfer reactions taking place inside a 100 bar hydrogen gas cell with an admixture of 0.25% deuterium that allows us to drastically reduce the amount of target material needed while still offering an adequate efficiency. Detailed simulations of the transfer reactions match the measured data, suggesting good understanding of the processes taking place inside the gas mixture. As a proof of principle we demonstrate the method with a measurement of the 2p-1s muonic x rays from a 5 
gold target.
© The Author(s) 2023
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