Speaker
Description
From dark matter and dark energy, to neutrino oscillations and the lack of antimatter in the universe, there is growing evidence that the Standard Model is incomplete. Tests of Quantum Electrodynamics (QED) with few-electron systems offer a promising avenue for looking for new physics, as QED is the best understood quantum field theory and extremely precise predictions can be obtained for few-electron systems. Unfortunately, despite decades of effort, QED is poorly tested in the regime of strong coulomb fields, precisely the region where new exotic physics may be most visible. I will present a new paradigm for probing higher-order QED effects using spectroscopy of Rydberg states in exotic atoms, where orders of magnitude stronger field strengths can be achieved while nuclear uncertainties may be neglected [1]. Such tests are now possible due to the advent of quantum sensing microcalorimeter x-ray detectors [2] and new facilities providing low-energy intense beams of exotic particles for precision physics. First measurements have been successfully conducted at J-PARC with muonic atoms [3], but antiprotonic atoms offer the highest sensitivity to strong-field QED. I will present an overview of the PAX project, a new experiment for antiprotonic atom x-ray spectroscopy with a large-area transition edge sensor (TES) x-ray detector at the ELENA facility at CERN [4]. I will show the first results from the test-beam measurements for PAX conducted in 2025 and 2026, show the first experimental spectra for antiprotonic atoms obtained with a TES detector, and discuss the next steps to improve the precision of the technique. Finally, I will present the preparations for the QED physics campaign that will be conducted within the ASACUSA collaboration, and briefly discuss long-term synergies with nuclear and new physics searches [5].
1] N. Paul et al, Physical Review Letters 126, 173001 (2021).
[2] J. Ullom and D. Bennett, Superconductor Science and Technology 28, 8 (2015).
[3] T. Okumura et al, Physical Review Letters 30, 173001 (2023).
[4] G. Baptista et al, Proceedings of Science 480, EXA-LEAP 2024 (2025).
[5] H. Liu et al, Phys. Rev. Lett. 135, 131803 (2025).