Exotic Atoms: A Testbed for QED

• Applicant: Jonas Sommerfeldt
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 546193616

This project aims to improve the accuracy of theoretical standard model predictions for transitions in exotic atoms in order to compare them to spectroscopy experiments. Such studies can verify one of the most important predictions of quantum electrodynamics (QED), the Lamb shift, in a parameter regime that was previously inaccessible and can help to identify signs of “new physics”. In exotic atoms, one or more electrons in the shell of the atom have been replaced by exotic, negatively charged particles. Examples of such particles are muons or antiprotons which are both much heavier than electrons and hence, orbit much closer to the nucleus than an electron in an equivalent state. It was already shown in the literature, that exotic atoms allow for tests of QED in parameter regimes that were previously inaccessible. For example, studies on QED corrections beyond the leading order in heavy atoms are heavily limited by the fact that the nuclear charge radius has to be extracted from experiment and is usually accompanied by a large uncertainty. This uncertainty also affects predictions of atomic energy levels and is usually larger than second-order QED effects in heavy atoms. However, studying QED effects in heavy atoms is particularly interesting since the interaction between the nucleus and the orbiting particle can not be treated perturbatively in this case and therefore, such studies can test the non-perturbative aspects of QED. Past Studies have shown that this problem can be avoided in exotic atoms since the smaller orbit of the heavier particle allows for transitions in which QED corrections are enhanced by orders of magnitude in comparison to the effect from the uncertainty of the nuclear charge radius. The necessary prerequisite to use this possibility are accurate calculations of second-order QED corrections in exotic atoms. While such calculations are in large parts available for electronic atoms, many contributions are unknown in the muonic and antiprotonic case. In this project, we aim to evaluate these unknown corrections in order to improve the theoretical values for the transition energies in exotic atoms. The calculations will help to analyse and guide experiments like the ones done as part of the muX project, within the QUARTET collaboration or within the HEATES collaboration and hence, will help to investigate properties of atomic nuclei, obtain a more complete verification of QED and search for “new physics”.

• DFG Programme: WBP Fellowship
• International Connection: France
• Host: Professor Dr. Paul Indelicato