For the previous twenty years, scientists have constructed a wide range of experiments, together with cryogenic detectors and tanks of liquid xenon, around the globe in hopes of recognizing the scantest indicators of elusive darkish matter particles. However time and time once more, they’ve come up empty-handed. Now a group of scientists suggest a very totally different method.
“How about if as an alternative of watching ever extra nuclei for a number of years, you may have some kind of detector recording scattering occasions for a really very long time as an alternative?” requested Sebastian Baum, a physicist at Stockholm College in Sweden.
Rocks themselves, which have existed for much longer than any physicist or their experiments, may very well be the laboratories that maintain traces of darkish matter. In an article revealed within the journal Bodily Assessment D, Baum and his colleagues name for figuring out and learning specific rocks internet hosting minerals with which darkish matter particles could have interacted. They may embrace historical signatures of weakly interacting huge particles, often called WIMPs.
Weak, however not useless
Buildings of darkish matter are thought to prop up the scaffolding of the universe, whereas shaping the billions of galaxies that develop inside them. Although the gravitational forces of darkish matter clumps appear clear, nobody has but detected the particles immediately, and in reality, physicists aren’t positive precisely what sort of particle darkish matter could be. WIMPs as soon as loved frontrunner standing because the almost certainly candidate for darkish matter particles, however physicists have to date didn’t detect them, even with more and more subtle and costly experiments.
Nonetheless, WIMPs have not been dominated out simply but, mentioned Dan Hooper, an astrophysicist at Fermilab in Batavia, Illinois. “Would an inexpensive individual take a look at these outcomes and say the probability of darkish matter being a WIMP is smaller than it was? Positive. However has that likelihood approached zero? No, it has not.”
Researchers within the 1990s recommended an identical method to Baum’s, probing bits of mica for a similar objective. However they lacked the know-how to make it work successfully and resolve the tracks that darkish matter particles may go away. “In recent times, the technical capability to investigate a chunk of mineral for very small tracks that may very well be deposited in it have actually improved, and that makes this far more highly effective than the outdated concepts,” Hooper mentioned.
A “gold mine” of information?
Baum’s group’s proposal focuses on two sorts of minerals embedded within the Earth’s crust. The primary contains deposits often called “marine evaporites,” shaped from evaporating lakes and inland seas, reminiscent of minerals referred to as halites and epsomites (like Epsom salts). These are almost as ubiquitous because the rock salt strewn throughout roads in winter to soften snow and ice. The second sort embrace “ultra-basic rocks,” like darkish inexperienced minerals referred to as olivine, shaped within the oceanic crust.
“These evaporite fields are intensive—they cowl a whole bunch or hundreds of sq. kilometers,” mentioned Clara Blättler, a geoscientist at Princeton College in New Jersey. She found the oldest deposit, in Russia, and others have been present in western Australia and Canada. Whereas ultra-basic rocks are shaped deeper, they’re generally thrust up by the crust by plate tectonics. “They exist in small slivers scattered all through the continents, however additionally they can lengthen for tens or a whole bunch of kilometers,” she mentioned.
Many of those minerals may very well be collected close to the floor of the Earth by drilling cores into the bottom. The rocks sometimes originated a whole bunch of thousands and thousands to greater than a billion years in the past—which might make them the longest-running darkish matter experiments ever. For enormous WIMPs, the particles would depart longer tracks, so scientists require extra materials to search out proof of them. Lighter WIMPs would depart smaller options that require higher-resolution experiments to select them out.
“The true problem is, whenever you get again to the lab, what data are you able to extract?” Hooper mentioned.
Scientists might want to determine slim tracks on the rocks, solely a nanometer broad, with instruments like microscopes and X-ray scattering experiments. However then they’ve to tell apart them from spurious alerts, reminiscent of these induced by even small quantities of background radiation, just like the decay of uranium-238 atoms.
Baum and his colleagues’ research reveals that it is potential to identify such alerts, in the event that they’re there, however scientists will not actually know if it’s going to work till at the very least small-scale experiments might be made efficiently. “Till it will get completed we cannot actually make certain it may be completed, however the identical factor was true about different, extra conventional darkish matter searches 20 years in the past,” Hooper mentioned.
—Ramin Skibba, Inside Science