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

TL;DR

The NEON experiment conducted a direct search for light dark matter using a NaI detector near a nuclear reactor, setting new exclusion limits on dark matter-electron interactions in the 1 keV/c$^2$ to 1 MeV/c$^2$ mass range.

Contribution

This study provides the first direct laboratory constraints on light dark matter produced by dark photon decay near a nuclear reactor.

Findings

No dark matter signal was observed in the energy range 1-10 keV.

Set the most stringent laboratory limit of $\sigma_e = 3.17 imes10^{-35}~ ext{cm}^2$ at 100 keV/c$^2$.

Extended the search for light dark matter below 100 keV/c$^2$ for the first time.

Abstract

We report new results from the Neutrino Elastic Scattering Observation with NaI (NEON) experiment in the search for light dark matter (LDM) using 2,636 kg$\cdot$days of NaI(Tl) exposure. The experiment employs an array of NaI(Tl) crystals with a total mass of 16.7 kg, located 23.7 meters away from a 2.8 GW thermal power nuclear reactor. We investigated LDM produced by the $\textit{invisible decay}$ of dark photons generated by high-flux photons during reactor operation. The energy spectra collected during reactor-on and reactor-off periods were compared within the LDM signal region of $1-10$ keV. No signal consistent with LDM interaction with electrons was observed, allowing us to set 90% confidence level exclusion limits for the dark matter-electron scattering cross-section ($\sigma_e$) across dark matter masses ranging from 1 keV/c$^2$ to 1 MeV/c$^2$. Our results set a 90% confidence level upper limit of $\sigma_e = 3.17\times10^{-35}~\mathrm{cm^2}$ for a dark matter mass of 100 keV/c$^2$, marking the best laboratory result in this mass range. Additionally, our search extends the coverage of LDM below 100 keV/c$^2$ first time.