More than a kilometer underground in an abandoned gold mine, one of the most important quests in physics has come up empty-handed in the search for the elusive substance known as dark matter, scientists announced on Wednesday.
The most advanced Earth-based search for the mysterious material that has mass but cannot be seen turned up “absolutely no signal” of dark matter, said Richard Gaitskell of Brown University, a scientist working on the Large Underground Xenon experiment. A detector attached to the International Space Station has so far also failed to find any dark matter.
Physicists released their initial findings on Wednesday after the experiment’s first few months of operation at the Sanford Underground Research Facility, which was built in a former gold mine in South Dakota’s Black Hills.
With 1,400m of earth helping screen out background radiation, scientists tried to trap dark matter, which they hoped would be revealed in the form of weakly interacting massive particles, nicknamed WIMPS. The search tried looking for the light fingerprint of a WIMP bouncing off an atomic nucleus of xenon cooled to minus-101°C.
However, nothing was found. The team plans to keep looking for another year, but members have doubts about finding dark matter with the current setup. They are already planning to build a more sensitive experiment on the site, using a bigger tank of xenon.
Still, physicists were upbeat, noting that the results eliminated some theoretical candidates for dark matter. And there are many more theoretical models to search for.
“The short story is that we didn’t see dark matter interacting, but we had the most sensitive search for dark matter ever performed in the world,” said Daniel McKinsey, a physicist at Yale University.
The LUX experiment was 20 times more sensitive than any previous experiments, they said. The proposed next experiment would be 1,000 times more sensitive still.
The lab is at the end of an old mining tunnel filled with pipes and electric cables. Gaitskell and McKinsey said the experiment has far less radiation interference from cosmic rays than any other dark-matter lab.
Essentially, scientists are searching for something they are fairly sure exists and is crucial to the entire universe, but they do not know what it looks like or where to find it. And they are not sure if it is a bunch of light particles that weakly interact or if it is more like a black hole.
“It’s ghost-like matter,” McKinsey said.
Researchers “are really searching in the dark in a way,” said Harvard University physicist Avi Loeb, who is not part of the LUX team. “We have no clue. We don’t know what this matter is.”
However, they keep looking. Gaitskell has been hunting for dark matter for 25 years.
“It’s like the pursuit of the Holy Grail, but hopefully this has a different outcome,” he said.