On June 16, 2023, 39 seconds after 3:22 P.M. and one mile beneath the Black Hills of South Dakota, there was a sudden flash of light.<\/p>\n
It happened in a dark, sealed tank of extremely cold liquid in a cavern where miners once chiseled gold from the walls. Caught by the tank\u2019s many cameras, the flash also sent an electric charge through hair-thin wires submerged in the liquid.<\/p>\n
The tank is the centerpiece of the LUX-ZEPLIN (LZ) experiment, one of several ongoing attempts by physicists to snare and study dark matter<\/a>, a shadowy something they suspect is everywhere\u2014yet somehow seems nowhere to be found. They\u2019ve sought it for the past 40 years by placing detectors in some of Earth\u2019s most silent and secluded spaces, places where dark matter\u2019s whispers might register. But every time so far, they\u2019ve come up empty, with every burst of light or surge of electricity having a more ordinary explanation.<\/p>\n On supporting science journalism<\/p>\n If you’re enjoying this article, consider supporting our award-winning journalism by subscribing<\/a>. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.<\/p>\n This flash from three years ago is different. The charge and light together seem to indicate a violent collision between an unknown particle and the nucleus of one of the detector\u2019s atoms. The event bears almost no resemblance to any of the \u201cbackgrounds\u201d\u2014mundane sources of flashes that mimic dark matter\u2014which the LZ collaboration\u2019s hundreds of scientists have spent their careers battling.<\/p>\n Yet the collision is also out of sync with the kind of dark matter signal they\u2019ve been searching for. That is, it\u2019s a total mystery. But after four decades of nothing, a new mystery is welcome.<\/p>\n \u201cI have been waiting for a positive result for, oh, my god, 40 years,\u201d says Katherine Freese, a theoretical physicist at the University of Texas at Austin, whose work helped inspire the search. \u201cSo you can bet I\u2019m very, very excited by the LZ results.\u201d<\/p>\n The LZ collaboration announced the finding in a presentation today at the TeVPA conference<\/a> in Japan. An accompanying paper has been submitted to Physical Review Letters. According to the project\u2019s best estimates, the flash\u2019s chances of being a statistical fluke are about half a percent (which is still far above the 0.00003 percent threshold used by particle physics experiments to hail a discovery).<\/p>\n The universe we see when we look out into space is almost impossible to countenance without dark matter. The stuff our telescopes can track is swirling too fast, forming too quickly into clumps that are too dense, to easily explain. The easiest explanation, in fact, is that, compared with the matter we can see, there must be five times more stuff that\u2019s invisible and inert, still carrying gravity\u2019s weight but emitting no light. This dark matter is ubiquitous and plentiful, but we have no idea what it\u2019s made of.<\/p>\n Detectors like LZ are predicated on a guess: that dark matter is made of weakly interacting massive particles (WIMPs). These are hypothetical particles that almost always slip through ordinary matter like ghosts. But very rarely, they should interact with it, colliding at random with an atom. LZ and its competitors are racing to pack as many atoms as possible into the quietest places they can find to catch these collisions.<\/p>\n Still, traces of background radioactivity sometimes break the subterranean silence, with that activity piercing through LZ\u2019s mile of protective bedrock or even seeping out of the materials lining the detector\u2019s walls. But physicists can discern many of these events from their best guess at dark matter\u2019s signals and try to reduce the incidents as much as they can. That a single unexplained event can carry so much statistical significance shows how incredibly sensitive the technology has become. \u201cWe made our meter so that the needle would jump when it saw an event like this,\u201d says Knut Mor\u00e5, a physicist at the University of Zurich and a member of the LZ collaboration. \u201cEverything is working as intended.\u201d<\/p>\n The collision from June 2023 meets most of the team\u2019s WIMPy expectations\u2014except that it\u2019s far too explosive. For LZ to find such a high-energy WIMP event, most standard theories say that it should have already seen dozens or hundreds of gentler ones\u2014which it has not. So if what LZ saw is a WIMP, this particle must be exceptionally odd\u2014interacting in a slightly different way with regular matter or somehow having been boosted to a higher speed.<\/p>\n \u201cGiven that we don\u2019t know what the dark matter is, it doesn\u2019t strike me as strange that it might not be exactly the thing we expect,\u201d says Hugh Lippincott, an associate professor at the University of California, Santa Barbara, and a member of the LZ collaboration.<\/p>\n Whether or not this signal will prove to be genuine is presently impossible to say. What\u2019s already certain is that it will spark a frenzy of papers seeking to explain how tweaks to various theoretical flavors of WIMPs could account for LZ\u2019s mysterious event. \u201cThey are potentially seeing other types of interactions which are perfectly reasonable,\u201d Freese says.<\/p>\n The collaboration itself also advises caution. \u201cWe shouldn\u2019t be comfortable claiming specific things about dark matter or about new physics based on one event,\u201d Mor\u00e5 says. Additionally, the team\u2019s scientists analyzed the data without \u201cblinding\u201d themselves to it, an approach to avoid bias that\u2019s considered the gold standard for particle physics. (They attempted an alternative approach called \u201csalting\u201d but stated that it was unsuccessful.)<\/p>\n Fortunately, more answers should arrive in the near future, based on a larger tranche of data that has been properly blinded. \u201cThis was 200 days of data. We actually have over 700 days blinded,\u201d says Richard Gaitskell, a professor at Brown University and co-spokesperson of LZ. \u201cSo that puts us in a strong position to study this.\u201d<\/p>\n Those data will either reveal this one event to be an anomaly or uncover more like it. In the latter case, two competing experiments, PandaX-4T and XENONnT<\/a>, will help determine whether LZ has really seen WIMPs or some as-yet-unknown background.<\/p>\n For now, the LZ collaboration is trying its best to manage expectations. \u201cYou get these flashes of, like, \u2018Wait, could this really be it?\u2019\u201d Mor\u00e5 says. \u201cBut it would be damaging to the analysis to be in that mindset, and I don\u2019t think many people are.\u201d Lippincott agrees, albeit with a nod toward the extraordinary. \u201cIt is far from any of the known backgrounds,\u201d he says, \u201cso it\u2019s hard not to wonder.\u201d<\/p>\n The mystery collision comes at a perilous time for the dark matter race. \u201cIt\u2019s a good moment for nature to give us this gift,\u201d says Juan Collar, a physicist at the University of Chicago, who is not part of the LZ collaboration. Detectors are becoming so large and so sensitive that they will soon be swamped with other ghostly particles called neutrinos that are generated in the sun and in Earth\u2019s atmosphere. At that point, the race would have to cease\u2014or at least to shift away from WIMPs to instead seek some other elusive quarry<\/a>.<\/p>\n \u201cHere\u2019s your last window of opportunity to see a WIMP\u2014if it\u2019s not there, you have to close up shop at some point in the next 10 years,\u201d Collar says. \u201cThis could be the beginning of something spectacular.\u201d<\/p>\n","protected":false},"excerpt":{"rendered":"On June 16, 2023, 39 seconds after 3:22 P.M. and one mile beneath the Black Hills of South…\n","protected":false},"author":2,"featured_media":603567,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[24],"tags":[85,46,370,141],"class_list":["post-603566","post","type-post","status-publish","format-standard","has-post-thumbnail","category-physics","tag-il","tag-israel","tag-physics","tag-science"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts\/603566","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/comments?post=603566"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts\/603566\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/media\/603567"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/media?parent=603566"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/categories?post=603566"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/tags?post=603566"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}