“Unexpected” events were detected in the world’s most sensitive dark matter experiment.
The researchers do not claim to have found dark matter, but they say that there is an unexplained and unexpected event rate found in the data from the experiment, and that they do not know the source.
The new breakthrough could be a sign of an entirely new type of particle or unexpected behavior that could force us to fundamentally change our understanding of physics.
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The results come from the XENON collaboration, which brought together researchers from around the world who were trying to detect dark matter. He did this using an experiment known as XENON1T, which was located deep underground in Italy.
Seeing evidence of dark matter would be one of the greatest scientific breakthroughs possible. Although it represents 85% of the matter in the universe, it has never been detected directly.
The XENON1T experiment aimed to find them by filling a detector with 3.2 tonnes of ultra-pure liquefied xenon, a chemical element. If a particle passes through this xenon, it creates a small flash of light – since most of these interactions occur from particles known to exist, scientists are able to predict how many there will be, and any excess would be evidence of some unexpected physique.
Scientists expected to find 232 such events by examining the data from the experiment. But in addition to these, they found a “surprising excess” of 53 events, which would not have been predicted in the data.
There is no definitive answer to the question of where these flashes come from. But some of the main explanations might offer new insight into some of the deepest questions in physics.
The flashes could, for example, be the result of the existence of a new particle, scientists say. The excess events are roughly in line with those which should be observed from hypothetical particles called axions, which can be produced in the Sun.
Solar axions are not candidates for dark matter, and their discovery would not be proof of its existence. But it would be the first time that scientists have detected this class of new particles, and their discovery could lead to new discoveries in fundamental physics as well as astrophysical phenomena, they say.
In addition, the solar axions of the first universe have been proposed as a source of dark matter, and their discovery could therefore help us understand how this mysterious substance came out.
This is the most likely explanation, scientists say, since the observed excessive events are in line with what is expected from the solar axions. There is about a 1 in 5000 chance that the results would be a random fluctuation rather than aligning with this assumption – but other explanations are also statistically significant, according to the researchers.
Otherwise, excess events could be the result of neutrinos, billions of billions of which pass through us and everything around us constantly. The result could be an indication that our understanding of the characteristics of these particles is wrong, a discovery that may require new physics to explain.
Perhaps the most pedestrian explanation is a new type of unexpected background noise, caused by the detector having more than one isotope called tritium inside than expected. It would only take a small number of these atoms to be present in the detector to explain the excess – but such a quantity would also be so small that it is not possible to detect whether it is there or not.
Scientists are currently upgrading the XENON1T experiment to its next phase, known as XENONnT. This will have a much larger amount of active xenon in its detector, as well as a lower background, allowing for cleaner data.
Researchers hope future work can help explain if unexpected events come from a contaminant in the detector, a statistical fluke – or a particle or behavior that has never been detected before , or even explained by current physics.
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