The LZ photodetectors, before they were installed in the experiment facility. (Matthew Kapust/Sanford Underground Research Facility)
In an experiment deep underground, a tiny flash of light may, ironically, mark the first detection of dark matter.This mysterious stuff should outnumber regular matter by a ratio of 5 to 1, but despite decades of searching, it's remained frustratingly elusive.Now, physicists are reporting a strange signal in the LUX-ZEPLIN (LZ) experiment that has all the characteristics expected of a leading dark matter candidate, and is tricky to explain through known physics. The results – which are yet to be peer-reviewed – were announced in a presentation at an astrophysics conference in Japan this week. The team is cautious about calling it too early: The event hasn't crossed the statistical threshold that allows scientists to effectively rule out other explanations."We're very intrigued to see this event in the data, in the region where we expect dark matter to show up and the competing backgrounds are very low," says Rick Gaitskell, a physicist at Brown University and spokesperson for LZ. "With only one event, we don't want to get ahead of ourselves. We are not claiming to have seen dark matter. But we have seen something interesting that we want to share with the scientific community for their input."As far back as the 1930s, astrophysicists realized that what we see out in the cosmos doesn't quite line up with our models of the Universe. There seems to be extra mass out there that mostly interacts with ordinary matter through its gravitational influence. Because it doesn't emit or reflect light, this mysterious substance was dubbed 'dark matter'.Exactly what form it takes remains unknown, so a variety of experiments have been searching for different potential candidates, to no avail.
