Scientists using the LUX-ZEPLIN experiment beneath South Dakota’s Black Hills have identified one unexplained particle interaction that resembles the signal expected from a dark matter particle. The team says the event is not a confirmed detection of dark matter.
The event was found in 220 days of data collected from March 2023 to April 2024. Researchers say it has survived repeated checks, making it the most compelling signal produced so far by the experiment, while cautioning that they are not claiming to have seen dark matter itself.
How the experiment searched for dark matter
The LUX-ZEPLIN experiment is based at the Sanford Underground Research Facility in South Dakota, inside an old gold mine. Its central tank contains ultra-pure liquid xenon and is surrounded by hundreds of light sensors.
The experiment tested whether a hypothetical dark matter particle known as a WIMP — a weakly interacting massive particle — could collide with a xenon nucleus. Scientists expected such a collision to create two flashes of light at a specific energy level. The LZ team found one event matching that pattern on June 16, 2023, after reviewing the data.
Key figures
- 27 percent: the estimated share of the universe made up of dark matter
- 68 percent: the estimated share attributed to dark energy
- 5 percent: the estimated share consisting of ordinary matter
Why the result is not a discovery yet
Dark matter has not been observed directly because it does not reflect light or electromagnetic radiation. Scientists infer its presence from gravitational effects, including the way galaxies rotate and how light bends around large clusters.
The latest interaction is important because the researchers say they understand the detector and its background signals well, and the event remained after multiple checks. But one unexplained event does not establish that a dark matter particle caused it. The LZ collaboration, an international team of 250 scientists and engineers from 38 institutions, has not called the result a confirmed detection.
Dark matter is distinct from dark energy. Scientists believe dark matter’s gravity helps account for structures in the universe, while dark energy is thought to drive galaxies apart and accelerate cosmic expansion. NASA has also announced a $4bn Nancy Grace Roman Space Telescope project to investigate both substances.
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