Study of the first excited state of the 4He nucleus in halo effective field theory

• Ano de defesa: 2024
• Autor(a) principal: Ader, Vinícius Bruno Bet
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: alpha-particle; anomalia ATOMKI; ATOMKI anomaly; canais acoplados; coupled channels; effective field theory; halo nuclei; núcleos halo; partícula alfa; teoria efetiva de campos
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/43/43134/tde-23102024-120558/

This work focuses on investigating the structure of 4He*, the first excited state (J^P=0^+) of the 4He nucleus, the alpha-particle. This excited state is found between the p-3H and n-3He thresholds, allowing for the use of coupled-channels formalism. The localization of this resonance between the aforementioned thresholds is a direct consequence of the breaking of the isospin symmetry, such that in the isospin limit both thresholds and the resonance would collapse to a single state. Moreover, a detailed description of the p-3H and n-3He scattering data and the 0_2^+ state properties play an important role in the radiative capture reactions 3H(p,g)4He* and 3H3(p,g)4He*. Both reactions contribute to the e^+e^- angular distribution produced out of the emitted photon and may shed light on the ATOMKI anomaly reported by Krasznahorkay et al., where an excess of produced lepton pairs suggests the existence of a new boson, with an approximate mass of 17 MeV, and that can be a possible candidate for dark matter. The 0_2^+ state is likely associated with a four-body excited Efimov state that has a 3+1 halo structure, making it suitable for investigation using the halo effective field theory (EFT) framework. Different phase shift parametrisations are used to fix the EFT couplings and predict the 0_2^+ state properties. Our results agree with most of the other theoretical studies but are in disagreement with the old results reported by Tilley et al. [Nucl. Phys. A 541(1):1104, 1992].