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Antiprotonic Atoms

Antiprotonic atoms, where an antiproton replaces the electrons around a nucleus, allow access to the strongest Coulomb fields on earth that be harnessed in the laboratory. The LKB team leads the project PAX, funded by an ERC Starting Grant, to perform highest-precision x-ray spectroscopy of antiprotonic atoms for strong-field QED tests.

Precision studies of antimatter atoms are now possible thanks to the ELENA (Extra Low ENergy Antiprotons) facility at CERN, operational since 2021, that provides slow (100 keV), bunched antiprotons that be captured in traps and used to form exotic systems.

At ELENA, we also participate in the PUMA collaboration that aims to use antiprotons to study the surface of exotic nuclei, and are members of the GBAR collaboration that seeks to study the effect of gravity on antimatter.

PAX

The PAX collaboration includes : LKB and LPNHE (France), NIST(USA), Technion (Israel), CERN, and RIKEN, Chubu University, Kyoto University, Rikkyo University, and Tokyo Institute of Technology (Japan).

The PAX project

The PAX project [1] is a new approach for testing strong-field QED via the x-ray spectroscopy of antiprotonic atoms. In these systems, orders of magnitude higher Coulomb fields can be obtained, acting like a magnifying glass for QED effects that become easier to measure. Using transitions between Rydberg states, uncertainties from nuclear properties can be avoided and two orders of magnitude sensitivity can be gained with respect to the best current experiments, making testing strong-field QED finally possible for a broad range of atomic species.

The realization of this project relies on the novel combination of two new technologies: slow antiproton beams at CERN, and quantum sensing x-ray detectors. The compatibility of these two requires new developments that will lead to a dedicated precision x-ray spectroscopy platform for antiprotonic atoms, with transverse applications beyond QED in nuclear and new physics searches.

PAX is led by Nancy Paul and was supported by an ANR Young Researcher grant for 2023-2024. PAX is funded by an ERC Starting grant for the period of 2024-2028. First test beam measurements should take place in 2025, and physics measurements after Long Shutdown 3 (LS3) at CERN.

To learn more about the physics case of PAX, see Testing Quantum Electrodynamics with Exotic Atoms, N. Paul et al, Physical Review Letters 126, 173001 (2021).

PUMA

antiProton Unstable Matter Annihilation

PUMA, antiProton Unstable Matter Annihilation, is a nuclear-physics experiment at CERN aiming at probing the surface properties of stable and rare isotopes by use of low-energy antiprotons. Low-energy antiprotons offer a very unique sensitivity to the neutron and proton densities at the annihilation site, i.e. in the tail of the nuclear density. Today, no facility provides a collider of low-energy radioactive ions and low-energy antiprotons: while not being a collider experiment, PUMA aims at transporting one billion antiprotons from ELENA, the Extra-Low-ENergy Antiproton ring, to ISOLDE, the rare-isotope beam facility of CERN. PUMA will enable the capture of low-energy antiprotons by short-lived nuclei and the measurement of the emitted radiations. In this way, PUMA will give access to the so-far largely unexplored isospin composition of the nuclear-radial-density tail of radioactive nuclei.

The LKB team contributes atomic theory for PUMA, and is invested in the long-term possibility of using antiprotonic atom x rays with PUMA also for nuclear physics.

Learn more about PUMA here :

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