Of all the different dark-matter detectors in the world, only one constantly comes with a positive signal. The results of the DAMA experiment in Italy are debated a lot – and now two experiments that they want to confirm using the same materials have again brought back the opposite results.
ANAIS, a dark matter detector conducted by the University of Zaragoza at Canfranc underground laboratory in Spain, delivered results that appeared to be contrary to DAMA.
But COSIN-100, driven by the collaboration between the Korean Invisible Mass Search and Yale University in the Yangyang Underground Laboratory in South Korea, is now producing a new way out. These results are similar to what ANAIS shed – but also slightly closer to the results DAMA has produced over the last 20 years.
This latest COSINE-100 report also comes after the announcement just a few months ago that the results of the collaboration have made no supports the findings of DAMA's dark matter.
On top of that, the two experiments only report on the preliminary results that have yet to be peer reviewed. So, what do we need to do from all of this?
Dark matter is one of the greatest mysteries of the universe. Something is there generating a force of gravity that can not be explained by the detected matter. The way stars and galaxies move indicates that up to 85 per cent of matter in the universe is actually dark matter.
We have yet to find it, but it can produce signatures that we can discover if we can perfect our technology and know what to look for.
One of these potential signatures is produced by hypothetical "massive particles with poor interaction", known as WIMPs. If these particles exist, we should be able to detect them through their collisions with electrons or atomic nuclei, which would cause charged particles on the Earth to produce light that can be raised by liquid xenones or crystal detectors.
DAMA registers WIMP detection since 1995, recorded as an annual fluctuation in the number of detected light strikes.
Due to the orbit of the Earth around the Sun and the orbit of the Solar System around the galactic center, the Earth should theoretically be exposed to a dark matter flux from the galactic halo around the top around June 2 and around December 2nd.
This is because the faster we move through the universe, the more dark matter should equal us, and the middle of the year is when the orbital speeds of the Earth and the Solar System are combined.
This is exactly what DAMA scientists claim their results show, but no other dark matter detector comes close to replication – not even XENON1T, hailed as the best stress in finding elusive things.
However, XENON1T uses liquid xenon detectors. Meanwhile, DAMA uses sodium iodide detectors in a tank filled with a liquid scintillator to indicate cosmic rays, so ANAIS and COSINE-100 are used.
But for all that, we are still in emotional territory.
ANAIS data did not cause fluctuations, but they were not in sync with the June peak of DAMA and December. And although the COSINE-100 result was closer than ANAIS, it still confirms that the DAMA modulation signal can not be from the default WIMP & [standard halo model] with [sodium iodide]"the researchers say.
So, why do these experiments, all so similar, produce such different results? Is anyone doing something wrong? Are minor differences detected in the detectors? If this plot gets any fatter, it will be pinned porridge.
"There really is not a conclusion to be drawn at this point, except that the uncertainty increases," said Juan Kolar, a physicist and dark matter at the University of Chicago, Illinois Nature. "But the instruments seem to have enough sensitivity to give final results soon."
It will probably take several more years of observation before physicists are closer to discovering the truth. We wait with a suffocated breath.
The results of COSINE-100 were presented at the conference "Results and Perspectives in Particle Physics" on March 12th. The results of ANAIS have been published on arXiv.