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Microscopic ab initio approach for the antiproton-nucleus annihilation

par Duerinck, Pierre-Yves
Président du jury Sparenberg, Jean-Marc
Promoteur Dohet-Eraly, Jérémy ;Lazauskas, Rimantas
Publication Non publié, 2025-09-26

Thèse de doctorat

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Résumé :

Low-energy antiprotons are promising probes for nuclear structure experiments. In particular, analysing the products of nucleon-antinucleon annihilations occurring during the decay of antiprotonic atoms is expected to provide unique observables to characterise the tail of proton and neutron densities. This great asset has motivated the PUMA (antiProton Unstable Matter Annihilation) project at CERN whose main goal is to investigate the properties of neutron skins and nucleonic halos in exotic nuclei. While the physics involved in the PUMA experiments is qualitatively understood, a fully microscopic description of antiproton-nucleus systems remains undeveloped. The primary goal of the present work is to study the simplest cases of antiproton-nucleus annihilation by solving the corresponding few-body Schrödinger equation. The present ab initio calculations are based on the Faddeev-Yakubovsky equations in configuration space, providing a rigorous framework for treating few-body scattering problems beyond two-body systems. The numerical resolution combines partial wave expansion and the Lagrange mesh method. As a first application, few-nucleon bound states up to four particles are studied. Their wavefunctions and energies are computed by using various nucleon-nucleon potentials. In addition, a benchmark study is conducted on the p+3H collision at low energy and the associated 0+ resonance. A fair agreement is obtained between different numerical methods. However, the theoretical results disagree with an R-matrix analysis of experimental data. Finally, antiproton-nucleus scattering states are calculated for light nuclei up to three nucleons: 1H, 2H, 3H, and 3He. These systems are particularly relevant to the theoretical development of the PUMA experiment. The sensitivity of the results to the choice of interaction models is investigated by comparing the level shifts of hydrogenic low-lying states computed with different nucleon-nucleon and nucleon-antinucleon interactions. Alongside traditional optical potentials, an alternative coupled-channel approach is also considered to further examine the influence of annihilation dynamics. Results indicate low model dependence when using well-constrained nucleon-nucleon interactions. However, the limited knowledge of nucleon-antinucleon forces leads to significant discrepancies in some partial waves. The level shifts can be extracted either from the wavefunction of the corresponding Rydberg states, or from the effective range parameters if accounting for corrections related to the internal structure of the nucleus. The consistency of the latter approach is assessed in two- and three-body systems for which a nice agreement between both methods is observed. Finally, a central property on which the PUMA project is based, that antiprotons are absorbed peripherally, is tested. By comparing the annihilation densities of low-lying hydrogenic states with the density of the target nucleus, the calculations provide a model-independent support for this key assumption.