The world's most sensitive dark matter detector just delivered 'significant results'

Have we finally detected dark matter?
Chris Young
Abstract image of dark matteragsandrew/iStock

Physicists at the LUX-ZEPLIN (LZ) experiment announced the results from their dark matter detector's first scientific run. 

The LZ detector is the world's most sensitive dark matter detector and the team announced the experiment is working as intended, and has released "significant results," a press statement reveals.

Though it did not detect dark matter in this first round of experiments, the signs are promising for a team that intends to use the machine to shed new light on one of the great mysteries of the universe.

Dark matter detector team kickstarts cosmic experiments

The LZ detector, located underground in South Dakota, is composed of several nested tanks of liquid xenon, each of which is 1.5 meters tall and 1.5 meters wide. It was placed underground so there would be as little background noise as possible for the experiment to detect elusive dark matter particles.

The hope is that a dark matter particle will fly through space and eventually bounce off one of the xenon atoms. This will agitate loose electrons into a flash that will be recorded by the experiment. 

The first run for the LZ detector lasted 60 days between December 25 and May 16. However, the scientists emphasized the fact that they're playing a long waiting game.

"We're looking for very, very low-energy recoils by the standards of particle physics. It’s a very, very rare process, if it's visible at all," Hugh Lippincott, a physicist at UC Santa Barbara and a member of the LZ team, said a press conference yesterday, July 7. "You can shoot a dark matter particle through 10 million light-years of lead and expect only one interaction at the end of that light-year."

Dark matter refers to the mysterious unaccounted-for matter that makes up roughly 85 percent of the entire mass of the universe. Though it has never directly been detected, we know it's out there because of the gravitational effect it has on observable space objects.

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One of the main candidates targeted by dark matter detection experiments, such as the DAMA/LIBRA experiment in Italy, is the WIMP, or Weakly Interacting Massive Particle. These particles have mass but barely ever interact with ordinary matter, which is why a super sensitive machine is required to detect them.

The LZ detector has 1,000 days of experiments scheduled

LZ is 30 times larger and 100 times more sensitive than its predecessor, the Large Underground Xenon experiment. Though construction started on the new detector in 2018, experiments were delayed by Covid-19. Now things seem to be running smoothly. "The collaboration worked well together to calibrate and to understand the detector response," said Aaron Manalaysay, a physicist at Berkeley Laboratory and a member of the LZ team, in a Berkeley Lab press release. "Considering we just turned it on a few months ago and during COVID restrictions, it is impressive we have such significant results already."

The world's most sensitive dark matter detector just delivered 'significant results'
The LUX-ZEPLIN dark matter detector. Source: Matthew Kapust/Sanford Underground Research Facility

The LZ detector researchers highlighted a total of 335 detections that looked promising during the machine's initial 60-day run. None turned out to be WIMPs, but the team was able to eliminate a mass range from future experiments. Ultimately, the team will be able to gradually eliminate mass ranges by pinpointing what masses the particles can't be. This will continually narrow the parameters for future experiments, making it more likely that WIMPs will be detected in subsequent attempts.