The LUX-ZEPLIN collaboration has reported a single particle interaction that may have come from dark matter, while stressing that the observation falls well short of a discovery. Researchers presented the result on September 1 at the TeV Particle Astrophysics conference in Tendo, Japan, after analyzing data from the detector nearly one mile underground in South Dakota.
The event looked like a xenon nucleus recoiling with an energy of about 248 kiloelectronvolts, with statistical and systematic uncertainties of 23 kiloelectronvolts each. The collaboration searched an extended energy range reaching approximately 270 kiloelectronvolts, allowing it to test dark-matter models that predict higher-energy collisions than conventional searches target.
LUX-ZEPLIN, known as LZ, uses 10 tonnes of ultrapure liquid xenon and hundreds of light sensors to detect extremely rare interactions. Its underground location at the Sanford Underground Research Facility and surrounding shields reduce cosmic rays and radioactive interference. The reported event occurred on June 16, 2023, within an exposure totaling 2.84 tonne-years and a roughly 220-day run.
The collaboration calculated a global significance of 2.6 sigma after accounting for the look-elsewhere effect, equivalent to roughly a 0.5 percent probability that known backgrounds produced an excess at least this striking somewhere in the tested models. The strongest local significance was 3.4 sigma. Particle physicists normally require 5 sigma before claiming a discovery, and the paper remains a preprint awaiting peer review.
Scientists cautioned that one event cannot establish what dark matter is. The signal could fit some weakly interacting massive particle models involving different internal states or momentum-dependent interactions, but an unidentified background or another particle process remains possible. Independent physicists told Nature and ABC News that further events with consistent properties would be essential before drawing a firm conclusion.
Dark matter is inferred from its gravitational effects on galaxies and is estimated to account for about 85 percent of matter in the universe, yet no experiment has directly identified its particles. LZ continues collecting data, and researchers will examine whether its future observations strengthen or weaken this unusual hint. Other detectors can also search their records for comparable high-energy nuclear recoils.
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