XENONnT's Ionization-Only Search Tightens Limits on Few‑GeV Dark Matter

XENONnT has reported a major new low-threshold search for light dark matter using 7.83 tonne-years of ionization-only data, finding no sign of a signal and tightening constraints on particles in the few-GeV mass range. The result is notable because the method lowers the experiment’s energy threshold, extending its reach to lighter candidates and moving it closer to a regime where solar neutrinos become an unavoidable background.

The XENON Collaboration said the search excludes spin-independent dark-matter-nucleon cross sections above (6.0 \times 10^{-45}) square centimeters for a dark-matter mass of 5 GeV/(c^2) at 90% confidence. The analysis reports spin-independent and spin-dependent limits for dark-matter masses between 3 and 8 GeV/(c^2). The result appears in “Light Dark Matter Search with 7.8 Tonne-Year of Ionization-Only Data in XENONnT,” by E. Aprile and collaborators, posted on arXiv as 2601.11296 and accepted by Physical Review Letters, which lists it as Phys. Rev. Lett. 137, 051003 (2026).

XENONnT is a dual-phase liquid-xenon time projection chamber — a detector that uses liquid and gaseous xenon to measure tiny particle interactions — at INFN’s Laboratori Nazionali del Gran Sasso in Italy. Its active target contains 5.9 tonnes of liquid xenon. In a standard search, researchers look for both scintillation light and ionization from a particle interaction. This analysis instead uses the ionization signal alone, known as an S2-only search. By not requiring a detectable flash of scintillation light, the method can probe smaller energy deposits, making it especially useful for hunting lighter dark-matter particles.

The scale of the analysis is also significant. It covers 579.5 days of blinded data from three science runs, SR0, SR1 and SR2, collected between May 2021 and March 2025. The paper says it is the first complete S2-only background model developed in XENONnT. The search is sensitive to nuclear recoils from 0.5 to 5.0 keVnr and electronic recoils from 0.04 to 0.7 keVee, both measures of very low deposited energy.

The main challenge at those thresholds was not ordinary low-energy recoils in the xenon, but instrumental background. The collaboration said the search was dominated by effects including cathode radioactivity and single-electron activity. To reduce that contamination, researchers excluded the 5% of runs with the highest single-electron rates. After accounting for those backgrounds, the collaboration reported no significant excess over expectation.

Beyond dark-matter-nucleon scattering, the analysis also sets new 90% confidence limits on dark-matter-electron scattering, axion-like particles and dark photons, improving on previous constraints, according to the paper. The broader importance of the result is that it pushes XENONnT closer to the point where coherent elastic neutrino-nucleus scattering, or CEvNS, becomes an irreducible background. In plain terms, that is where solar neutrinos begin to mimic the kind of tiny nuclear recoils a dark-matter search is trying to find, limiting how cleanly experiments can separate signal from background.