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Precision measurments of quantum transitions in exotic atoms

Project description

Matter–antimatter investigations with exotic atoms

Theoretically, every particle has an antimatter particle just like itself but with opposite charge. These particles were created with the Big Bang, from which emerged equal amounts of matter and antimatter. However, when a matter particle meets its antimatter counterpart, they annihilate each other so our observation of much more matter than antimatter in the universe does not make sense. Exotic atoms provide an interesting test bench for matter–antimatter investigations. In exotic atoms, one or more subatomic (matter) particles has been replaced by a different subatomic particle with the same charge. With the support of the Marie Skłodowska-Curie Actions programme, the QUARTET project is investigating quantum transitions in exotic atoms for new insight into matter and antimatter behaviours.


Based on our understanding of the universe, we, who are made of matter, should not exist. This is due to the fact that the subatomic world is largely indifferent between matter and antimatter, predicting that they would be created in almost equal amounts in a big-bang scenario, and subsequently annihilate to form pure energy. This conundrum is called the baryon asymmetry problem. It is one of the major and most pressing unsolved questions in science today. One way of addressing this problem is to look for deviations between precision measurements and Standard Model predictions. However, a major limitation arises in the stage of comparison with theory due to nuclear-structure effects. Conducting measurements with exotic atoms overcomes this limitation, either by comparing measured properties between atoms and anti-atoms directly with no input from theory, or by measuring systems composed of particles with no internal structure. QUARTET - Quantum transitions in exotic atoms, will pursue both directions through two complementary experimental campaigns:
1. Muonium spectroscopy using the most intense low-energy muon beam at PSI.
2. Antihydrogen spectroscopy using the most intense low-energy proton beam at the ELENA beamline at CERN.
QUARTET will focus on transitions in the microwave region of the electromagnetic spectrum, namely the classical Lamb-Shift, which for Antihydrogen has an added value: If no difference between matter and its counterpart is observed, this measurement will provide the first determination of the antiproton charge radius.


Net EU contribution
€ 203 149,44
Raemistrasse 101
8092 Zuerich

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Schweiz/Suisse/Svizzera Zürich Zürich
Activity type
Higher or Secondary Education Establishments
Total cost
€ 203 149,44