Speaker
Description
Until recently, the transition of 4He from its ground state to the 0+ first excited state was commonly interpreted as a monopole excitation or "breathing mode" [1]. This mode involves symmetric expansion and contraction of the nucleus, akin to a balloon inflating and deflating, while preserving its spherical shape.
Recent calculations using the No Core Gamow Shell Model (NCGSM), which treats the 4He nucleus as an open quantum system, challenge this previous view. By incorporating multiple reaction channels, such as [1H + 3H], [3He + n], and [2H + 2H], the NCGSM provides a more accurate solution to the N-body problem and predicts the excitation function for 4He decay across these channels.
To explore these predictions, we first analyzed correlation functions for the [1H + 3H] and [2H + 2H] channels from Ni+Ni reactions at incident energies of 32 and 52 MeV/A using the FAZIA+INDRA apparatus. Our study highlights the limitations of the apparatus as well as limitations of correlation function methods. These finding will be presented.
In addition, we propose an alternative experimental approach to extract the branching ratios of 4He decay channels as a function of excitation energy. This approach involves a 4He(n,n') experiment using the NFS neutron beam in combination with the ACTAR TPC, filled with pure 4He gas. This method aims to track the evolution of the weight of each decay channel as a function of excitation energy, providing critical constraints on theoretical calculations.
These studies offer new insights into the structure and decay mechanisms of 4He, opening pathways to refine our understanding of light nuclei as open quantum systems.
References:
[1] S. Kegel et al., Measurement of the alpha particle monopole transition form factor challenges theory: A low energy puzzle for nuclear forces, Phys. Rev. Lett., 130, 152502 (2023).
[2] N. Michel, W. Nazarewicz. and M. Ploszajczak, Description of the Proton-Decaying 0+2 Resonance of the alpha Particle, Phys. Rev. Lett., 131, 242502 (2023); 133, 239901 (2024).
