Mysterious signal detected in underground US detector — possibly the first trace of dark matter

At the Sanford Underground Research Facility in South Dakota, the LUX-ZEPLIN (LZ) experiment has recorded a single unusual particle collision that scientists cannot yet explain through ordinary physical processes. The new analysis of the data was presented at the TeV Particle Astrophysics conference, held in Japan in late August and early September.

The characteristics of the recorded event match what could theoretically result from contact with a dark matter particle — the mysterious substance that, according to physicists' calculations, makes up most of the mass of the Universe but has never been directly observed.

A detector deep underground

The LZ facility sits nearly 1.5 kilometers underground, in a former gold mine. The thick layer of rock acts as a natural shield, blocking cosmic radiation that would otherwise interfere with the ultra-precise measurements. The project brings together 250 scientists and engineers from 39 research institutions around the world.

At the heart of the facility is a detector containing ten tonnes of ultra-pure liquid xenon. Researchers are waiting for the exceedingly rare moment when a dark matter particle collides with a xenon atom's nucleus and transfers part of its energy to it. Such a collision would produce a tiny flash of light and a burst of electrons — both of which the equipment is designed to detect.

What the scientists were looking for

In the new analysis of data collected between March 2023 and April 2024, researchers focused on "more energetic interactions" than in previous studies, broadening the search for possible signs of particles known as WIMPs (weakly interacting massive particles). Physicists consider these one of the leading candidates for dark matter.

According to Reuters, astrophysicist Alvine Kamaha, who took part in the analysis, compared dark matter to "cosmic glue" that helped galaxies like our own Milky Way form. Without it, the Universe would have evolved in a completely different way, and the structures that eventually gave rise to the Solar System might never have formed at all.

WIMPs are theorized to have mass but interact extremely weakly with ordinary matter — meaning enormous numbers of them could pass through the Earth, detectors, and even the human body without ever leaving a trace. That's why experiments like LZ spend years waiting for that single rare collision capable of producing a faint but measurable signal.

Around Prague, based on reporting by novinky.cz