First Direct Search for Light Dark Matter Using the NEON Experiment at a Nuclear Reactor.

Area of Science:

• Particle Physics
• Cosmology
• Experimental Nuclear Physics

Background:

• The existence of dark matter is inferred from gravitational effects, but its composition remains unknown.
• Light dark matter (LDM) presents a viable candidate, with various theoretical models predicting its interactions.
• Nuclear reactors are powerful sources of high-flux photons, potentially producing dark photons that decay into LDM.

Purpose of the Study:

• To search for light dark matter (LDM) produced by the invisible decay of dark photons.
• To set exclusion limits on the dark matter-electron scattering cross-section (σe) using experimental data.
• To explore the LDM parameter space, particularly below 100 keV/c².

Main Methods:

• Utilized the Neutrino Elastic scattering observation with NaI (NEON) experiment, employing 16.7 kg of NaI(Tl) crystals.
• Collected 2636 kg·days of exposure near a 2.8 GW nuclear reactor, comparing reactor-on and reactor-off data.
• Analyzed energy spectra in the 1-10 keV signal region to identify potential LDM interactions with electrons.

Main Results:

• No statistically significant signal consistent with LDM interactions was observed.
• Established 90% confidence level exclusion limits on σe for dark matter masses from 1 to 1000 keV/c².
• Achieved the best laboratory upper limit for σe at 3.17×10⁻³⁵ cm² for a dark matter mass of 100 keV/c².

Conclusions:

• The NEON experiment has placed stringent constraints on LDM models, particularly those involving dark photon decays.
• The study provides the first experimental coverage for LDM below 100 keV/c² under the assumed dark photon decay scenario.
• Future searches can build upon these results to further probe the nature of light dark matter.