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<\/div>An array of sensors at the LUX-ZEPLIN dark matter experiment in South Dakota<\/p>\n
Matthew Kapust\/Sanford Underground Research Facility<\/p>\n<\/div>\n<\/figcaption><\/figure>\n<\/p>\n
The latest hunt for dark matter has come up empty handed so far, but the upside is that physicists can now set the tightest constraints ever on the nature of this mysterious substance. New measurements from the LUX-ZEPLIN (LZ) experiment in South Dakota mean we are either closer than ever to finding particles of dark matter or ruling out the most popular explanation for it.<\/p>\n
Dark matter<\/a> doesn\u2019t interact much with regular matter or with light, so we can\u2019t see it. We only know that it exists because of its gravitational effects, but those effects indicate it makes up over 80 per cent of all matter. The leading explanation for dark matter has long been that it is made up of weakly interacting massive particles (WIMPs), but hunts for these fundamental entities have found nothing yet.<\/p>\n LUX-ZEPLIN, a dark matter detector made of 7 tonnes of liquid xenon buried 1.5 kilometres underground, is the most sensitive yet \u2013 but after 280 days of searching, it hasn\u2019t found any WIMPs. \u201cWe\u2019re the world\u2019s best at not finding dark matter,\u201d says LZ spokesperson Chamkaur Ghag<\/a> at University College London.<\/p>\n <\/p>\n While this result may seem like a disappointment, it has allowed physicists to place tight constraints on the nature of dark matter<\/a>, reducing the range of properties it could have. The constraints are nearly five times tighter than the previous best, drastically narrowing down the possibilities for WIMPs. This work was presented at two physics conferences \u2013 TeV Particle Astrophysics<\/a> in the US and LIDINE<\/a> in Brazil \u2013 on 26 August.<\/p>\n \u201cIt\u2019s as if we\u2019ve been told there\u2019s some magical fish that lives in the ocean and we have no idea where it is,\u201d says Ghag. \u201cWe get into the ocean, swim around, get out, get a snorkel, swim around, still don\u2019t find it, get a submarine.\u201d If the magical fish is a WIMP, researchers have now explored about 75 per cent of the ocean without finding it, he says.<\/p>\n \u201cThis is the next big step forward, and it\u2019s one in a long line of such steps,\u201d says Dan Hooper<\/a> at the Fermi National Accelerator Laboratory in Illinois, who wasn\u2019t involved in this work. \u201cIn any one of these steps forward, it might be fair to say we don\u2019t expect to see anything. But if you take enough of these steps, it seems not unlikely that we could see something.\u201d<\/p>\n At this point, many initially popular ideas for possible types of WIMPs<\/a> have been ruled out. There are still some left, but LZ isn\u2019t done yet \u2013 it is expected to make 1000 days of observations in total before it ends in 2028. \u201cIf LZ doesn\u2019t see WIMPs, and the next generation detector, XLZD, does not see WIMPs, it\u2019s kind of over for WIMPs,\u201d says Ghag. The XLZD project is still in the planning phase.<\/p>\n