Dipole Strength Distribution of ^{8}He and Decay Characteristics

Area of Science:

• Nuclear Physics
• Quantum Mechanics

Background:

• Drip-line nuclei exhibit weak binding and extended neutron densities, leading to unique low-energy dipole responses.
• The helium-8 nucleus is the most neutron-rich bound nucleus, with a mass-to-charge ratio of A/Z=4.

Purpose of the Study:

• To measure the dipole response of the helium-8 nucleus, including the four-neutron decay channel for the first time.
• To compare experimental results with advanced theoretical models.

Main Methods:

• Differential Coulomb-excitation cross-section measurements.
• Analysis of decay channels, including four-neutron emission.
• Comparison with coupled cluster and three-body theoretical calculations.

Main Results:

• A total dipole strength of ∑B(E1)(E*<15 MeV)=0.95(16)e² fm² and a dipole polarizability of αD=0.61(1) fm³ were extracted.
• The dipole continuum is predominantly characterized by two-neutron emission, even above the four-neutron decay threshold.
• No four-neutron final-state correlations were observed, but significant two-neutron and helium-6 + neutron correlations were found.

Conclusions:

• The excited dipole mode in helium-8 suggests a helium-6 + 2n structure.
• The findings highlight the importance of considering multi-neutron emission channels in exotic nuclei.
• Experimental data align with theoretical predictions, validating nuclear structure models for neutron-rich systems.