A mile beneath South Dakota, in what used to be a gold mine, one of the most sophisticated experiments in the world lies. Called LUX-Zeplin, it hopes to finally observe dark matter: the hypothetical substance that should make up 85 percent of the matter in the universe.
It was turned on two months ago. It has not found dark matter, but in those 60 days, it allowed researchers to put the most stringent constraints on what dark matter might be. The device will have to run out for 1,000 days to realize its full sensitivity, but this preliminary results confirm that the design is sound.
Dark matter is invisible, it doesn’t interact with light. Observational evidence is so far circumstantial, based on the need for extra matter (or new physics) to explain the rotation of galaxies and the structures of the Universe. One possibility is that dark matter is made of weakly interacting massive particles (WIMPs), and that’s what LUX-Zeplin is hunting for. Occasionally, a WIMP might interact with an atom among the seven tons of liquid xenon in the detector.
The possible interaction would free electrons, which will be detected. Even if it's not seeing any interaction, this tells physicists where dark matter isn’t. Just 60 days have diminished the possible mass range where these WIMPS might exist.
“The collaboration worked well together to calibrate and to understand the detector response,” Berkeley Lab's Aaron Manalaysay who, as physics coordinator, led the collaboration’s efforts to produce these first physics results, said in a statement. “Considering we just turned it on a few months ago and during COVID restrictions, it is impressive we have such significant results already.”
The paper with the first results can be read online here. The detector is now pushing in the region known as the neutrino fog (formerly the neutrino floor). This is the area where the effects of neutrinos, also particles that hardly interact with matter, can be observed by the detector. However, scientists are confident that enough data will be collected to separate the neutrinos from the potential wimps.
“We plan to collect about 20 times more data in the coming years, so we’re only getting started. There’s a lot of science to do and it’s very exciting,” LZ spokesperson Hugh Lippincott of the University of California, Santa Barbara, explained.
The search for dark matter doesn’t pass through this experiment alone. The Large Hadron Collider has started its third run and physicists there hope to see weird decays of the Higgs Boson indicating the existence of dark matter. And obviously, astronomical observations by upcoming telescopes will constrain the properties of this plausible form of matter even more.
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