Periodic Reporting for period 1 - SENUC (Super Exotic NUClear systems at the limit of stability: Core excitations in halo nuclei and few-nucleon emitters.)
Reporting period: 2021-05-01 to 2023-04-30
The SENUC action aims to improve our understanding of processes related to the most exotic nuclear systems observed in radioactive ion beam facilities. What are the limits of nuclear stability? How do nuclear systems behave beyond the dripline boundaries? By studying the properties of exotic halo nuclei and few-nucleon emitters, the action will help assess how shell evolution shapes the limits of the nuclear chart, which could help address open questions regarding the strong force and nucleon-nucleon correlations. To that end, the researchers sought to describe core-excitation effects and reduce the gap between standard few-body reaction models and the microscopic many-body structures of nuclei at the limits of nuclear existence. The specific objectives of the action include:
- Description of the scattering of two-nucleon halo nuclei (formed by a compact core and two valence neutrons) within a four-body framework including core excitations. The small separation energies and large radii associated with diffuse halo nuclei implies a large probability of valence excitation into continuum breakup states. Within this action, the effect of collective core excitations was studied and found to be important for the scattering of deformed cores on light targets. The results will help study processes involving the heaviest known halo systems, for which an inert core assumption is not realistic.
- Description of the relative-energy distributions in the decay of unbound core+n+n systems, called two-neutron emitters. It was found that a decay state, built by time-evolving a non-stationary resonant state, can describe the asymptotic properties of the decay fragments. Interestingly, core excitations influence the total decay width and the shape of the relative-energy distributions.
- Description of the above topics including microscopic inputs. This requires the folding of microscopic nuclear densities with a nucleon-nucleon interaction, leading to effective potentials to be used within the usual few-body models. This line of action is still in progress.
The SENUC action results provide important building blocks for more advance studies on the dynamics of very exotic nuclear states.
- Description of the scattering of two-nucleon halo nuclei (formed by a compact core and two valence neutrons) within a four-body framework including core excitations. The small separation energies and large radii associated with diffuse halo nuclei implies a large probability of valence excitation into continuum breakup states. Within this action, the effect of collective core excitations was studied and found to be important for the scattering of deformed cores on light targets. The results will help study processes involving the heaviest known halo systems, for which an inert core assumption is not realistic.
- Description of the relative-energy distributions in the decay of unbound core+n+n systems, called two-neutron emitters. It was found that a decay state, built by time-evolving a non-stationary resonant state, can describe the asymptotic properties of the decay fragments. Interestingly, core excitations influence the total decay width and the shape of the relative-energy distributions.
- Description of the above topics including microscopic inputs. This requires the folding of microscopic nuclear densities with a nucleon-nucleon interaction, leading to effective potentials to be used within the usual few-body models. This line of action is still in progress.
The SENUC action results provide important building blocks for more advance studies on the dynamics of very exotic nuclear states.
The activities performed for the duration of the action include:
- Theoretical derivation of the formalism to incorporate collective core excitations in continuum-discretized coupled-channel calculations induced by three-body (core+N+N) nuclei, such as two-neutron halo systems. Implementation of approximated formulas in a computer code. Calculations for the scattering of 12Be.
- Development of a sudden eikonal formalism to describe momentum distributions and angular correlations in proton-target knockout reactions induced by two-neutron halo nuclei, including the possible effect of collective core excitations. Implementation in a computer code. Calculations for the knockout from 11Li, 14Be and 17B.
- Mathematical description of the relative-energy distributions of three-body decays, in particular for two-neutron emitters, involving the construction of a decay state from the evolution of a non-stationary resonance state. Implementation in a computer code. Application to 16Be and 13Li.
- Work on the inclusion of microscopically-derived folding potentials within the standard few-body description of structure and reactions. Implementation and calculations for 12Be, 8He are still pending.
- Description of inclusive breakup measurements by incorporating structure overlaps within a three-body model. This serves as a bridge between standard few-body models and the full microscopic description. Calculations are in progress for 197Au(9Be,8Be).
So far, the action has produced two peer-reviewed publications:
- Phys. Lett. B 840 (2023) 137875 [open access]
- Phys. Rev. C 104 (2021) 024618 [arXiv:2107.11081]
Five manuscripts are in preparation and/or to be submitted.
Results of the action have been presented at several international meetings, including invited talks at:
- ECT* Workshop on “Nuclear Physics at the Edge of Stability” (NPES), Online. 28 June - 1 July 2021.
- Workshop of the Hellenic Institute of Nuclear Physics (HINPw6), Online. 14-16 May 2021.
and regular talks at:
- Direct reactions with Exotic Beams (DREB2022), organized by IGFAE and USC. Santiago de Compostela (Spain), 26 June - 27 July 2022.
- European Nuclear Physics Conference (EuNPC2022), organized by IGFAE and USC. Santiago de Compostela (Spain), 24-28 October 2022.
- Neutron-Unbound Systems Around the Dripline (NUSAD) workshop, Online. Organized by FRIB/NSCL, 13-14 July 2021.
- Theoretical derivation of the formalism to incorporate collective core excitations in continuum-discretized coupled-channel calculations induced by three-body (core+N+N) nuclei, such as two-neutron halo systems. Implementation of approximated formulas in a computer code. Calculations for the scattering of 12Be.
- Development of a sudden eikonal formalism to describe momentum distributions and angular correlations in proton-target knockout reactions induced by two-neutron halo nuclei, including the possible effect of collective core excitations. Implementation in a computer code. Calculations for the knockout from 11Li, 14Be and 17B.
- Mathematical description of the relative-energy distributions of three-body decays, in particular for two-neutron emitters, involving the construction of a decay state from the evolution of a non-stationary resonance state. Implementation in a computer code. Application to 16Be and 13Li.
- Work on the inclusion of microscopically-derived folding potentials within the standard few-body description of structure and reactions. Implementation and calculations for 12Be, 8He are still pending.
- Description of inclusive breakup measurements by incorporating structure overlaps within a three-body model. This serves as a bridge between standard few-body models and the full microscopic description. Calculations are in progress for 197Au(9Be,8Be).
So far, the action has produced two peer-reviewed publications:
- Phys. Lett. B 840 (2023) 137875 [open access]
- Phys. Rev. C 104 (2021) 024618 [arXiv:2107.11081]
Five manuscripts are in preparation and/or to be submitted.
Results of the action have been presented at several international meetings, including invited talks at:
- ECT* Workshop on “Nuclear Physics at the Edge of Stability” (NPES), Online. 28 June - 1 July 2021.
- Workshop of the Hellenic Institute of Nuclear Physics (HINPw6), Online. 14-16 May 2021.
and regular talks at:
- Direct reactions with Exotic Beams (DREB2022), organized by IGFAE and USC. Santiago de Compostela (Spain), 26 June - 27 July 2022.
- European Nuclear Physics Conference (EuNPC2022), organized by IGFAE and USC. Santiago de Compostela (Spain), 24-28 October 2022.
- Neutron-Unbound Systems Around the Dripline (NUSAD) workshop, Online. Organized by FRIB/NSCL, 13-14 July 2021.
The inclusion of core excitation effects in reactions involving by three-body nuclear systems, such as two-neutron halo nuclei and two-neutron emitters, provides new insights into the dynamics of very exotic nuclei. The results of the SENUC action will help in the interpretation of new experiments in radioactive ion beam facilities, which have access to increasingly complex nuclear systems. The main mathematical derivations and computer codes developed could help other researchers working in the field.