Physicists have been making an attempt for a number of years to double-check a sign from an experiment buried in an Italian mountain—a sign that appeared an terrible lot like a darkish matter suspect often called a WIMP. Previous makes an attempt to see that sign with different initiatives had fallen flat, and now, the experiment most just like the unique one has printed its outcomes: It, too, discovered nothing.

No one is aware of what darkish matter is—it’s a placeholder time period used to explain the invisible stuff we are able to solely detect by way of its gravity—however one candidate to elucidate darkish matter is named WIMPs, or Weakly Interacting Massive Particles. The concept is that some subatomic particles do have mass however work together so weakly with extraordinary matter that we’ve but to detect them. People largely seek for WIMPs by placing extraordinarily delicate detectors deep within the floor, the place they’re shielded from most of the influences which may produce deceptive alerts.

The experiment that purportedly detected a WIMP sign in 2017 is the DAMA/LIBRA experiment. DAMA/LIBRA makes use of sodium iodide crystals as targets for darkish matter; the thought is that if darkish matter passes by means of the crystals, they’ll get excited and grow to be a bit of brighter. Other experiments that seek for WIMPs by different means, just like the XENON1T in Italy and XMASS-I in Japan, have not been capable of finding the sign that DAMA/LIBRA is seeing.

Enter the COSINE-100 experiment, which is predicated in a laboratory 2,300 toes underground in South Korea. COSINE-100 makes use of over 200 kilos of the identical sodium iodide goal, making it a superb mimic of DAMA/LIBRA. COSINE-100 has been on the lookout for a WIMP sign since 2016. Its first search turned up zilch. Its subsequent search, the outcomes of that are published as we speak in Science Advances, ran from October 2016 by means of July 2018. The COSINE-100 crew reported that they discovered simply as little as they did final time, which might imply the top of the street for the controversial DAMA/LIBRA outcomes.

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“Our team found that what DAMA observed could not be the dark matter under most basic assumptions of how we think WIMPs should interact with ordinary matter,” Reina Maruyama, a physicist at Yale University and a co-author of the recent paper, told Gizmodo in an email. “We have not yet strongly tested DAMA’s observation of annual modulation, which DAMA argues is due to dark matter. That is our next focus.”

DAMA/LIBRA uses a different approach to try to detect dark matter than most experiments. While other setups either look for dark matter particles by colliding known particles or looking for a background signal, DAMA/LIBRA has observed the regular modulation of some unexplained signal that Earth has received in different amounts, depending on how it’s oriented, since the experiment began operation in 2003. Other initiatives have did not see the identical sign, which is within the X-ray band of the electromagnetic spectrum. But, maybe because of the manner the experiment manages its noise, as reported by Ethan Siegel in Forbes, the DAMA/LIBRA of us might have been seeing a sign the place there wasn’t one to start with.

The COSINE-100 paper “does not change at all the dark matter investigation,” said DAMA/LIBRA spokesperson Rita Bernabei, a physicist at Italy’s National Institute for Nuclear Physics and the University of Rome Tor Vergata. “Considering that so many models are possible about related astrophysical, nuclear and particle physics aspects and the many existing uncertainties on related parameters and assumptions, a serious comparison is quite a complicated and uncertain job both from experimental and theoretical points.”

Bernabei emphasized that the two detectors are not the same and that the COSINE-100 team’s method can produce “large uncertainties and biases.”

“Although our results do not favor the dark matter interpretation of DAMA assuming the most widely used dark matter model, we could not say DAMA is nothing,” said Hyun Su Lee, a co-author of the recent paper and a physicist at the Center for Underground Physics at the Institute for Basic Science in South Korea, in an email to Gizmodo. In other words, DAMA has some sort of signal, but COSINE-100 results suggest it was not dark matter.

Some physicists, like Dan Hooper at the University of Chicago, do feel that the newer experiment has done a good job of showing that the DAMA/LIBRA experiment is not the way we’ll find WIMPs, if they exist.

“My view is that over the past 10 to 15 years, it has steadily become more and more difficult to think that the signal being reported by the DAMA collaboration was really the consequence of dark matter particles. One after the other, experiments came out with results that failed to confirm the claims of DAMA,” Hooper said in an email. “Most of the physicists I know (including myself) essentially gave up on this possibility years ago.”

“That being said, we all agreed that it would be most convincing if an experiment could be carried out that used exactly the same kind of target material that DAMA used,” Hooper added. “The COSINE experiment is precisely that, and the fact that they did not see anything is really a big nail in the coffin of dark matter interpretations of DAMA. I still don’t know what it is that DAMA is seeing—maybe it’s some weird background, or just some mistake they’ve somehow made. But whatever is going on, it doesn’t seem to have anything to do with dark matter.”

WIMPs have been losing steam as the forerunning dark matter candidate. Axions—much smaller particles—have become a hotter topic in recent years, and even huge objects like primordial black holes remain a hypothesis in some circles. No one has been able to certify any direct detections of dark matter yet, but plenty of experiments are looking in different spaces.

“I am excited to see what we find with the large WIMP experiments like XENONnT, LZ, and SuperCDMS,” Maruyama said. “I also find axions compelling and am excited to be working on HAYSTAC and its extensions. With COSINE, we can continue to search for WIMPs and of course, the next steps are to carry out the ultimate test of DAMA—annual modulations.” The annual modulations are that weird signal itself, which ebbs and flows over the course of each year. Just because it’s not dark matter doesn’t mean it’s not intriguing.

In physics, finding nothing can be just as enlightening as finding something; in the case of dark matter, it can tell scientists that they need to look elsewhere.

More: If We Live in a Sea of Dark Matter, This Tiny Mirror Might Be Able to Detect It