Search for a Neutron Dark Decay in ^{6}He.

Area of Science:

• Particle Physics
• Cosmology
• Nuclear Physics

Background:

• Neutron dark decays are proposed to resolve discrepancies in neutron decay experiments.
• These decays offer a potential dark matter candidate detectable in halo nuclei.
• The decay of Helium-6 (⁶He) into Helium-4 (⁴He), a neutron, and a dark particle (χ) provides a unique signature.

Purpose of the Study:

• To search for evidence of neutron dark decays.
• To establish experimental limits on the branching ratio of these decays.
• To constrain dark neutron decay models and their implications for dark matter.

Main Methods:

• Utilized a high-intensity ⁶He+ beam at the Grand Accélérateur National d'Ions Lourds.
• Searched for coincident neutron signals in conjunction with the ⁶He decay.
• Employed a high-efficiency neutron detector for precise signal identification.

Main Results:

• Established an upper limit on the dark decay branching ratio (Brχ) of ≤4.0×10⁻¹⁰ (95% Confidence Level).
• Translated this limit into an upper bound for dark neutron branching ratio of O(10⁻⁵) using the Fornal-Grinstein model.
• Achieved improvements of one to several orders of magnitude over existing global constraints.

Conclusions:

• The experiment provides the most stringent limits to date on neutron dark decays.
• These results significantly constrain theoretical models of dark neutron decay.
• The findings impact the search for dark matter candidates originating from neutron decays.