Gran Sasso: assioni, “bricks” of dark matter theorized 43 years ago by Roberto Peccei (died June 1)

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For now only an excessmore events are recorded than expected; it may still be a malignant fluctuation, a joke of statistics that will perhaps disappear with subsequent observations. Or, more trivially, it is a false alarm, due to an unexpected contamination of radioactive elements in the apparatus. But the news that Xenon1T he found something abnormal in his data has traveled around the world.

The result was announced by theNational Institute of Nuclear Physics, which manages and finances i National Laboratories of the Gran Sasso, and by the physicists of the Xenon1T experiment who built the apparatus and analyzed the data collected. Xenon1T one of the world’s most sensitive detectors for research dark matter particles.

The hunt for this exotic form of matter, which does not shed light and whose presence only deduced thanks to its gravitational effects, one of the most important challenges of modern physics. Our universe made up for about a quarter of this mysterious component; without dark matter, galaxies, including our Milky Way, would not be able to form and orbit permanently for billions of years, assuming the characteristic forms that are so familiar to us.

The complicated matter because these particles so elusive and different from all those we know, they could be extremely heavy, real monsters in terms of mass.

But there are theories that instead foresee that this thin gas that pervades a large part of the universe is formed by ultra-light particles, almost evanescent.

The anomaly to which Xenon1T refers may have been produced by this second type of object, the axions.

It’s about particles hypothesized in 1977 by Roberto Peccei, a physicist of Italian origin who died very recently, and from Helen Quinn, an American physicist of Australian origin. To explain some strange characteristics of the decays due to strong interactions, the two hypothesized the presence of a new symmetry that could manifest itself in a neutral, very light and extremely elusive particle.

Since their hypothesis tidied up and cleaned up a topic that had been at the center of a long series of disputes, Franck Wilczek, a prank Nobel prize winner, proposed the name assione, borrowing it from a famous detergent from the 1950s. Wilczek’s joke took hold and since then this is the name that is used for these phantom particles, never discovered until now, and which could be the main component of dark matter.

The excess of underlying events recorded by Xenon1T could be the first sign of axions produced by the Sun. but the authors of the article themselves suggest other hypotheses. The most banal, a tiny contamination of Tritium, a radioactive isotope of hydrogen which, by disintegrating, would have produced the excess of signals. Alternatively there could be explanations linked to subtle anomalies in the characteristics of neutrinos. In short, the results are far from conclusive.

If they were solar axions, a modulation in their frequency should be seen at periods of greater or lesser distance from the Sun. If the effect due to statistics or contamination, increasing the sensitive mass of the detector, as Xenon1T is preparing to do, it they should soon collect more convincing data to confirm or deny the presence of a signal. Listen.



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