Nuclear Reactor Data Excludes Cosmological Triangle in Search for Axion-Like Particles

We report new constraints on axion-like particle (ALP) using data corresponding to a sodium iodine target exposure of 3063\, kgdays from the neutrino elastic scattering observation with NaI (NEON) experiment. A 16. 7\, kg of thallium-doped sodium iodide target was located 23. 7 meters from a 2. 8\, GW thermal power nuclear reactor. We searched for ALPs produced by high-flux photons by comparing the energy spectra of data collected during reactor-on (1596\, kgdays exposure) and reactor-off (1467\, kgdays exposure) periods. No signal consistent with ALP interaction was identified, allowing us to set exclusion limits at the 95\% confidence level. Our limits cover previously unexplored regions for both photon couplings (g₀) and electron couplings (g₀₄) for axion masses around 1\, MeV/c². Notably, the NEON data excludes the unconstrained region identified by laboratory-based searches for photon couplings within the ``cosmological triangle'' for the first time. The observed 95\% confidence level limits reach as low as g₀ of 4. 33 10^-8\, GeV^-1 and g₀₄ of 1. 10 10^-9 for axion masses of 1. 7\, MeV/c² and 1. 0\, MeV/c², respectively.