Signal XENONnT Sets World-Leading Limits on Axion-Like Particles Near the 'Neutrino Fog' Threshold

Summary

The XENON Collaboration published results in Physical Review Letters (137, 051003) on July 30, 2026, reporting world-leading upper limits on sub-keV axion-like particles (ALPs) and dark photons. Using the liquid xenon detector at Italy's Gran Sasso National Laboratory, the team analyzed 7.83 tonne-years of ionization-only (S2-only) data collected over 579 days across three science runs. The result pushes sensitivity for light dark matter close to the "neutrino fog" — the point where solar neutrinos become an irreducible background indistinguishable from a dark matter signal. No statistically significant excess was observed, and the collaboration set improved 90%-confidence upper limits on spin-independent and spin-dependent dark matter-nucleon scattering in the 3-GeV-and-above mass range, as well as on dark matter-electron scattering. The results will inform the design of the next-generation 60-tonne XLZD detector. The rival LZ experiment reported in December 2025 world-leading WIMP limits in the 3-9 GeV range along with the first 4.5-sigma detection of solar neutrinos via coherent elastic neutrino-nucleus scattering, formally marking the arrival of the neutrino fog era for direct dark matter detection.