Speaker
Description
The PAX experiment is a new effort to improve the study of x ray transitions in antiprotonic atoms for testing Bound State QED (BSQED) [1,2]. By selecting transitions between circular Rydberg states, where the bound antiproton resides orders of magnitude closer to the nucleus than an electron, whilst avoiding any nuclear overlap with its wavefunction, the dominant uncertainties that limit the accuracy of measurements in HCI are neutralized. Employing novel microcalorimeter detector technologies, namely Transition Edge Sensors (TES) [3], PAX aims at testing BSQED by measuring these transitions at levels of accuracy up to two orders of magnitude greater than previous efforts with Germanium detectors [4].
We present the latest measurements from PAX's 2025 and 2026 test-beamtimes at CERN, where the energies of x-ray transitions in the 50-150 keV range in antiprotonic Silicon and Zirconium were determined at eV-level accuracies. We discuss the necessary data processing steps to tackle the charged-particle induced background and correct for the detector's dynamic response to beam-prompt events.
[1] - N. Paul, et al., “Testing Quantum Electrodynamics with Exotic Atoms,” in Phys. Rev. Lett., vol. 126, no. 17, p. 173001, 2021.
[2] - G. Baptista, et al., “Towards Precision Spectroscopy of Antiprotonic Atoms for Probing Strong-field QED,” in Proceedings of International Conference on Exotic Atoms and Related Topics and Conference on Low Energy Antiprotons — PoS(EXA-LEAP2024). Austrian Academy of Sciences, Vienna.: Sissa Medialab, p. 085, 2025.
[3] - J. N. Ullom and D. A. Bennett, “Review of superconducting transition-edge sensors for x-ray and gamma-ray spectroscopy”, in Superconductor Science and Technology, vol. 28, no. 8, p.084003, 2015
[4] - P. Roberson et al.,"Strong interaction and mass measurements using antiprotonic atoms" in Phys. Rev. C, vol. 16, p. 1945, 1977.