We report new results from the neutrino elastic scattering observation with NaI (NEON) experiment in the search for light dark matter (LDM) using <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:mn>2636</a:mn><a:mtext> </a:mtext><a:mtext> </a:mtext><a:mi>kg</a:mi><a:mo>·</a:mo><a:mi>days</a:mi></a:mrow></a:math> of NaI(Tl) exposure. The experiment employs an array of NaI(Tl) crystals with a total mass of 16.7 kg, located 23.7 m away from a 2.8 GW thermal power nuclear reactor. We investigated LDM produced by the of dark photons, a well-motivated mechanism 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 on the dark matter-electron scattering cross section (<c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:msub><c:mi>σ</c:mi><c:mi>e</c:mi></c:msub></c:math>) across dark matter masses ranging from 1 to <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mrow><e:mn>1000</e:mn><e:mtext> </e:mtext><e:mtext> </e:mtext><e:mi>keV</e:mi><e:mo>/</e:mo><e:msup><e:mrow><e:mi mathvariant="normal">c</e:mi></e:mrow><e:mrow><e:mn>2</e:mn></e:mrow></e:msup></e:mrow></e:math>. Our results set a 90% confidence level upper limit of <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"><h:mrow><h:msub><h:mrow><h:mi>σ</h:mi></h:mrow><h:mrow><h:mi>e</h:mi></h:mrow></h:msub><h:mo>=</h:mo><h:mn>3.17</h:mn><h:mo>×</h:mo><h:msup><h:mrow><h:mn>10</h:mn></h:mrow><h:mrow><h:mo>−</h:mo><h:mn>35</h:mn></h:mrow></h:msup><h:mtext> </h:mtext><h:mtext> </h:mtext><h:mrow><h:msup><h:mrow><h:mi>cm</h:mi></h:mrow><h:mrow><h:mn>2</h:mn></h:mrow></h:msup></h:mrow></h:mrow></h:math> for a dark matter mass of <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"><j:mrow><j:mn>100</j:mn><j:mtext> </j:mtext><j:mtext> </j:mtext><j:mi>keV</j:mi><j:mo>/</j:mo><j:msup><j:mrow><j:mi mathvariant="normal">c</j:mi></j:mrow><j:mrow><j:mn>2</j:mn></j:mrow></j:msup></j:mrow></j:math>, marking the best laboratory result in this mass range. Additionally, our search extends the coverage of LDM below <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:mrow><m:mn>100</m:mn><m:mtext> </m:mtext><m:mtext> </m:mtext><m:mi>keV</m:mi><m:mo>/</m:mo><m:msup><m:mrow><m:mi mathvariant="normal">c</m:mi></m:mrow><m:mrow><m:mn>2</m:mn></m:mrow></m:msup></m:mrow></m:math> for the first time, assuming the specific of dark photons. Published by the American Physical Society 2025

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