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The search for dark matter just got a fresh pair of eyes. A test run of the LUX-ZEPLIN (LZ) detector in South Dakota has shown it to be the most sensitive dark matter detector yet created, and researchers are getting ready to turn it on and start hunting in earnest.

LZ consists of a huge titanium tank filled with 10 tonnes of extremely pure liquid xenon. When a particle from outside the tank hits a xenon atom, it creates a burst of light that is measured by a series of detectors surrounding the tank. The properties of that light can then be analysed to determine what type of particle caused it. To shield the xenon from particles and radiation that we know don’t come from dark matter, the tank is surrounded by an even larger tank of purified water and the whole thing is buried more than a kilometre underground in an old gold mine.

“The centre of LZ is the purest place on Earth, maybe in the solar system. There’s no other volume of space on or in this planet that is that free of radiation and dust,” says LZ team member at University College London. “We can only handle about a gram of dust in the detector – 3 grams of dust and we won’t be able to find anything.”

Decades of hunting for dark matter particles have been unsuccessful so far, so researchers have taken to making more and more sensitive detectors. A 3.5-month test run that ended in April showed that LZ is the most sensitive yet. “We’ve taken a few months of data, and when we looked at that data what we said was ‘oh, shit – we’re already the world’s best’,” says Ghag. “It’s like if you built a new car and took it around the block, and in that quick drive around the block you broke the world landspeed record.”

Regardless of sensitivity, though, three months wasn’t long enough to actually find dark matter. Even if some did come through the detector during that time, we wouldn’t have enough data to say for sure what it was, says Ghag.

“For now it’s kind of a weird thing, we’re saying that we’re the best in the world at finding nothing,” he says. “But the prospect of finding new physics a few years from now is entirely feasible.”

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