Physicists believe dark matter makes up 85% of the mass of the universe, but despite its theoretical abundance, there is no direct proof that it exists. Now, researchers at Brown are closing in on that sought-for proof.
In the LUX-ZEPLIN, or “LZ,” experiment, researchers at Brown helped analyze data from 2023 and early 2024 containing a signal that could potentially be the first detection of a dark matter particle.
Richard Gaitskell, professor of physics and spokesperson for the LZ experiment, explained that the Sun’s orbit in the Milky Way doesn’t match up with current calculations for the amount of mass and number of stars in the galaxy. He explained that there is not enough mass in the Milky Way to allow our solar system to orbit, and this suggests that something may be missing from the standard model of physics.
Chongwen Lu GS, who is involved with the LZ experiment, said that this might be because the current model does not account for dark matter — a massless and invisible substance that scientists believe holds galaxies together.
“If we can find the dark matter, then we might find the missing parts of elementary particles,” he said.
According to Gaitskell, the main goal of the LZ experiment is to find evidence of dark matter. The experiment uses an LZ detector, a chamber filled with liquid xenon located a mile underground and surrounded by water. This detector looks for interactions from hypothetical weakly interacting matter particles, or WIMPs.
When a WIMP — hypothesized to be a dark matter particle — enters the chamber, it interacts with the liquid xenon, causing the xenon to emit both photons and electrons. The LZ detector can then record particles by using light detectors at the top and bottom of the chamber, Benjamin Almquist GS, who is involved with the LZ experiment, wrote in an email to The Herald.
The researchers believe an interaction provides evidence of dark matter if the detector gives a signal for a process called nuclear recoil.
“The dark matter candidate that we are looking for only interacts with the detector through something called the nuclear recoil,” said Charles Kong GS, who is involved with the LZ experiment.
While the signal data strongly suggests the existence of the particles, it has not reached the threshold necessary to be considered a “discovery,” explained Chen Ding GS, who is involved with the LZ experiment.
The chances of the signal coming from known processes — as in, not evidence of dark matter — are “very small, but not zero,” said Associate Professor of Physics Loukas Gouskos, who hosted Gaitskell’s talk at a physics colloquium on Friday.
Gaitskell also said that further analysis on the signal is required.
“We now need to go back and review everything, try to make sure that we really understand exactly how the detector was behaving, what we know about the detector, and what we still need to review,” Gaitskell said.
“We’re in a great position now to do a new analysis with more data, and we’ll be able to see whether we’re seeing more events and whether those events are consistent with dark matter or not,” Gaitskell added.
Almquist wrote that the next steps are “continuing to take more data, monitoring detector stability and health and continuing analyses with the same focus and detail as the previous ones.”
Gouskos called the findings “one of the most exciting results we have for the last few years.”
“We are living in very exciting moments,” Gouskos said. “We are all looking forward to seeing what will happen with this case.”
Angel Lopez is a senior staff writer covering Science and Research. He’s a sophomore from Tyler, Texas and planning to study neuroscience and literary arts. In his free time, you can find him playing ping pong, listening to music, or reading.
