Candidate Resonant Tetraneutron State Populated by the ^{4}He(^{8}He,^{8}Be) Reaction

Area of Science:

• Nuclear Physics
• Particle Physics
• Quantum Mechanics

Background:

• The existence of the tetraneutron (a state composed of four neutrons) has been a long-standing question in nuclear physics.
• Understanding multi-neutron systems is crucial for comprehending nuclear structure and the forces governing atomic nuclei.

Purpose of the Study:

• To search for experimental evidence of a resonant tetraneutron state.
• To investigate the properties of weakly interacting four-neutron systems.

Main Methods:

• The study employed a double-charge-exchange reaction: ^{4}He(^{8}He,^{8}Be).
• Experiments were conducted at a beam energy of 186 MeV/u.
• Missing-mass spectroscopy was utilized to detect the resulting particles.
• A large positive Q value in the reaction facilitated near-recoilless conditions for the four-neutron system.

Main Results:

• A candidate resonant tetraneutron state was identified in the missing-mass spectrum.
• The state's energy was measured at 0.83±0.65(stat)±1.25(syst) MeV above the four-neutron decay threshold.
• The observed state exhibited a statistical significance of 4.9σ.

Conclusions:

• The experimental results provide evidence for a resonant tetraneutron state.
• The findings contribute to the ongoing quest for understanding exotic nuclear matter and neutron-bound systems.
• The employed reaction mechanism efficiently produced and allowed for the study of the weakly interacting four-neutron system.