First Search for Bosonic Superweakly Interacting Massive Particles with Masses up to 1  MeV/c^{2} with GERDA

Area of Science:

• Particle Physics
• Cosmology
• Astrophysics

Background:

• Dark matter constitutes a significant portion of the universe's mass.
• Superweakly interacting massive particles (super-WIMPs) are theoretical candidates for dark matter.
• Previous searches have not constrained bosonic super-WIMPs in the keV-scale mass range.

Purpose of the Study:

• To perform the first search for bosonic super-WIMPs as keV-scale dark matter candidates.
• To constrain the properties of axion-like particles and dark photons using the GERDA experiment.
• To set new limits on the couplings of super-WIMPs to electrons.

Main Methods:

• Utilized the GERDA experiment, designed for neutrinoless double-beta decay searches.
• Employed high-purity germanium detectors enriched in ⁷⁶Ge.
• Searched for pseudoscalar and vector super-WIMPs in the mass range of 60 keV/c² to 1 MeV/c².

Main Results:

• No evidence for a dark matter signal consistent with bosonic super-WIMPs was observed.
• The most stringent direct limits on the couplings of super-WIMPs with masses above 120 keV/c² were established.
• Specific limits were set for axion-like particles (g_ae < 3×10⁻¹²) and dark photons (α'/α < 6.5×10⁻²⁴) at 90% credible interval for a 150 keV/c² mass.

Conclusions:

• The GERDA experiment provides the strongest constraints to date on certain types of keV-scale bosonic dark matter.
• The search excludes a parameter space for super-WIMPs, particularly axion-like particles and dark photons.
• Future dark matter searches can build upon these results to further probe the nature of dark matter.