The XENON1T detector, the largest search for "heavy" dark matter, ruled out the existence of light forms of dark matter and "groped" the first hints of the existence of unexpectedly heavy particles of this mysterious substance, project participants said at a press conference in the Italian laboratory of Gran Sasso.
“So far, only one thing can be said - this damned particle is still hiding from us. On the one hand, we did not find traces of its existence in the mass range up to 200 GeV. On the other hand, our models do not exclude the existence of heavier WIMPs. We even have hints of this in the data, although their statistical significance is small - only one sigma, and I would like to believe that this is not an accident,”said Elena Aprile, an official representative of the XENON1T collaboration.
The world behind a dark screen
For a long time, scientists believed that the universe consists of the matter that we see, and which forms the basis of all stars, black holes, nebulae, dust clusters and planets. But the first observations of the speed of movement of stars in nearby galaxies showed that the stars on their outskirts move in them at an impossibly high speed, which was about 10 times higher than calculations based on the masses of all the stars in them showed.
The reason for this, according to scientists today, was the so-called dark matter - a mysterious substance, which accounts for about 75% of the mass of matter in the Universe. Typically, each galaxy has about 8-10 times more dark matter than its visible cousin, and this dark matter holds the stars in place and prevents them from scattering.
Today, almost all scientists are convinced of the existence of dark matter, but its properties, in addition to its obvious gravitational influence on galaxies and galaxy clusters, remain a mystery and a subject of controversy among astrophysicists and cosmologists. For a long time, scientists have assumed that it is composed of superheavy and "cold" particles - "wimps" that do not manifest themselves in any way, except by attracting visible clusters of matter.
Scientists are trying to find such particles today using giant underground detectors filled with absolutely pure xenon. The nuclei of the noble gas atoms, as previously assumed by scientists, had to interact with the "WIMPs" in a special way, which could be detected by observing the flashes of light inside the liquefied xenon.
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Over the past two decades, scientists have created about a dozen such detectors with increasing volume and mass, none of which has been able to detect traces of xenon-WIMP interactions. Particular hopes were pinned on the XENON1T project - a detector built in the Italian laboratory of Gran Sasso in 2014 and containing a record 3.5 tons of xenon, which is about 10 times the mass of all its competitors.
The key to the universe
The first results, presented by the XENON1T team in November last year, again turned out to be "zero" - a team of more than one hundred physicists from 21 countries of the world could not find any significant traces of the existence of "WIMPs" in a very wide range of masses and energies.
Aprile and her colleagues today presented the results of an analysis of the full dataset, which broadly confirmed their preliminary findings, with a few minor exceptions. As the scientists note, they managed to exclude the possibility of the existence of light "WIMPs" with masses from 6 to 30 GeV, and virtually zero the chances of detecting particles with a mass of up to 200 GeV.
On the other hand, the data they have collected do not contradict and, according to Aprile herself, indicate that the particles of dark matter actually have a much higher mass than physicists previously assumed.
“Our task now is very simple - we just need to continue observing, and at the same time lower the noise level and increase the sensitivity. As it seems to me, we will either be able to go to the VIMPs after the next update of the detectors, or we will finally close the question of their existence,”the physicist continues.
According to her, the XENON1T participants are already assembling a new version of the detector, the mass of xenon in which will be increased to four tons, and the level of interference will be reduced by at least 10 times. Its installation will be completed this year, and it will receive the first scientific data in mid-2019.
