Underground experiment casts doubt on controversial dark matter claim

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The COSINE-100 detector was constructed to breed a controversial claim of the detection of dark matter.

Jay Hyun Jo

Underground experiment casts doubt on controversial dark matter claim

Twenty years in the past, physicists with the Dark Matter (DAMA) experiment in Italy’s subterranean Gran Sasso National Laboratory announced they had detected particles of dark matter—the mysterious stuff whose gravity presumably holds the galaxy collectively. Now, the primary experiment designed to straight check DAMA’s controversial claim has launched its first information. Physicists working with the COSINE-100 detector in South Korea say they see no signal of dark matter—however nonetheless want a pair extra years to actually put the screws to the DAMA claim.

“They can’t rule out the DAMA signal yet,” says Katherine Freese, a theoretical physicist on the University of Michigan in Ann Arbor who shouldn’t be concerned in both experiment. “But the exciting thing is that they’ll be able to rule it out.” Or, as could also be much less probably, affirm it.

Astrophysical observations present invisible dark matter makes up 85% of all matter. Our personal galaxy is believed to reside inside an unlimited cloud of the stuff. However, scientists nonetheless don’t know what dark matter is. For a long time, experimenters have hunted for particles of it floating about, largely to no avail. To seek for dark matter, physicists deploy ultrasensitive detectors deep underground, the place they’re shielded from cosmic rays and different background radiation.

However, since 1998, the DAMA collaboration has claimed to have seen simply such a sign. The staff’s detectors include sodium iodide crystals doped with thallium, which produce flashes of sunshine when a particle of some kind—common or dark matter—strikes a nucleus inside the materials and sends it flying. The DAMA staff has seen a yearly variation within the collision fee that might be a robust signal of dark matter, as Freese and a colleague predicted in 1986.

If our Milky Way galaxy is shrouded in dark matter, then because the solar wheels in regards to the galactic middle, it ought to usually plow right into a wind of dark matter particles. Moreover, as Earth circles the solar, it ought to alternately rush into and out of that wind, inflicting the speed of dark matter collisions to wax and wane over the course of the 12 months. If dark matter consists of theorists’ favourite candidate particle, referred to as weakly interacting huge particles (WIMPs), the sign ought to peak in June and backside out in December—simply what DAMA sees.

Several different detectors have did not see the sign. However, these detectors use heavier components corresponding to xenon, silicon, and germanium for the goal nuclei, DAMA researchers say, which might clarify the discrepancy. “Even taking those results as they are, considering the large experimental and theoretical uncertainties there could be space for compatibility,” says Rita Bernabei, a physicist on the University of Rome Tor Vergata and chief of the DAMA staff.

To kind via the confusion, COSINE researchers constructed a detector that additionally makes use of thallium-doped sodium iodide crystals. “I got into this field to test the DAMA result, and I was surprised others hadn’t,” says Reina Maruyama, a physicist at Yale University and co-spokesperson for the 50-member COSINE staff. Since 2016, the 106-kilogram detector has been accumulating information 700 meters underground at Yangyang Underground Laboratory, on South Korea’s jap coast. And its first 59.5 days of information show no sign of dark matter, COSINE researchers report right this moment inNature.

So does the COSINE consequence nix the DAMA claim? Not fairly. With solely 2 months of information, COSINE researchers couldn’t search for the telltale annual variation, however merely seemed for an extra of occasions above the backgrounds created by extraneous radiation. The lack of an extra guidelines out the chance that DAMA is seeing WIMPs, Maruyama says. But Bernabei says the check is simply too weak to try this. “The modeling of a background is a quite uncertain procedure and at low energy is in general not reliable,” she says.

However, Freese says WIMPs are already dominated out—by DAMA’s personal information. The argument is hard, but when dark matter particles are WIMPs, that are presumed to work together with the nucleus in a very easy approach, then the peaks and valleys in DAMA’s annual cycle ought to shift by 6 months for lower-energy occasions, Freese explains. And low-energy information that DAMA offered earlier this 12 months present an unshifted oscillation. DAMA might be seeing another type of dark matter particle, Freese says. Bernabei argues that DAMA might nonetheless be seeing WIMPs.

All agree that to actually put the DAMA claim to the check, COSINE researchers should look for a similar annual variations that DAMA sees—which may help pull a weaker sign out of the background. COSINE already has 2 years of information within the can, Maruyama says, and it’ll want one other three years to make that check. Two different experiments are additionally attempting to straight problem the DAMA consequence with sodium-iodide detectors.

Ultimately, all physicists hope to detect dark matter. So Maruyama says she would “love to” reproduce the DAMA sign. If COSINE can’t do this, Freese says, “We may never know what created the DAMA signal.”



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