A research experiment taking place one mile below Earth’s surface is on track to discovering dark matter, largely thanks to Brown researchers.
Though dark matter has yet to be detected by researchers, it is believed to constitute 85 percent of the universe’s total matter, said Richard Gaitskell, professor of physics and one of the experiment’s lead researchers. Dark matter is the “dominant component” of matter in the universe, but “because it doesn’t interact with light,” it’s difficult to detect, Gaitskell said.
Scientists know dark matter exists because of the way gravity has been shown to act on structures in outer space, Gaitskell said.
The Large Underground Xenon, known as LUX, is a multi-institutional effort to try to detect the elusive matter. The experiment’s development and execution has been five years in the making, Gaitskell said.
“The design of LUX is bigger and more sensitive than any previous experiment,” Gaitskell said. “If you’re looking for very rare particles, then size is important.”
Developing a machine sensitive enough to detect dark matter is especially difficult.
“It is like being at the Super Bowl with 75,000 people clapping, and they’re trying to hear if a person is breathing. That’s the difficulty of extracting the signal they do,” said Savvas Koushiappas, assistant professor of physics. Koushiappas was not involved in the LUX experiment.
Located in an old mine shaft in South Dakota, the LUX contains about one third of a ton of liquid Xenon in a core bath. When particles in the LUX interact with the Xenon bath, the collisions produce flashes of light. Photomultiplier tubes moniter these flashes of light and convert them into electronic signals that can be recorded, Gaitskell said. Dark matter particles interact with the Xenon bath in a unique way, facilitating the possibility of detecting the presence of the evasive particles.
The results of the LUX experiment also prove early findings claiming to have discovered dark matter false, said Jeremy Chapman GS, who works with Gaitskell and was involved with the LUX experiment.
“It’s hard to convey to people that having a null result like we had is as important as having a positive result,” said David Malling GS, who also works on the LUX project. “You learn as much from it. We have no clue what dark matter is or is not, so finding what it is not is equally as valid as finding what it is.”
People have been trying for 30 years to figure out what dark matter is, and by showing that some of these theories are wrong, the findings allow researchers to focus on the theories that may actually be right, Malling added.
“Over the next couple years, we will continue to improve the LUX, make it even better, make it run longer,” Gaitskell said. By 2016, the researchers hope to run a machine 20 times as big, he added.
The project was a three-month pilot, Malling said. Following the findings, the team will run a subsequent year-long LUX experiment.
The experiment is funded primarily by the U.S. Department of Energy and the National Sciences Foundation but has also received substantial funding from Brown, the state of South Dakota and a private donor, Gaitskell said.
When it comes to dark matter, “there’s no bigger slice of the pie to be digging into,” said Chapman. “It’s one of the remaining mysteries of the universe.”
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