An experiment in the search for ever-elusive dark matter has sent back some strange and exciting signals,media reported. Abnormalities may not be dark matter itself, but they may be a sign that scientists are looking for it in the right orbit. Scientists have offered three possible explanations for these signals, one for unnecessary interference and the other for new physics principles.
The XENON1T experiment was designed to look for particles of dark matter, which is thought to be five times more than conventional matter. Since dark matter should be everywhere, XENON1T is mindful of the rare interactions between its particles and conventional matter. To that end, it stared at a huge jar filled with tons of liquid radon. When some of the outside particle stripes pass through the tank, it excites the argon atoms, creating flashes and free electrons, which XENON1T can detect.
But it’s not just dark matter that can do this, but known particles can trigger similar signals. To filter out these, the team calculated how many background events were expected and then checked for more signals than that. Sure enough, the team now reports “amazingly many events.” The expected background is 232 events during this period, but 53 more events were identified on this basis. It’s a huge number, and there must be something wrong. But what exactly is this?
The researchers say there are three possible explanations. The first is that this may be just an unrecognized source of background interference. The signal is consistent with the radon impurities in the tank, requiring only a few of the 10 700 million thorium atoms to produce an excess signal. It is frustrating that no instrument can sensitively detect such a tiny amount of radon in a tank, so this possibility cannot be ruled out.
In addition, the team says, the most suitable data is an imaginary elementary particle called an axis, especially particles produced by the sun. These particles were first proposed in the 1970s to address the so-called “strong CP destruction” problem. It was later decided that if they had a certain mass, the axes produced billions of years ago could explain the strangeness of our dark matter.
Although these particular solar axes will not be candidates for dark matter, if confirmed, this would mark the first time any kind of axiome has been discovered. This in itself is a huge discovery that suggests that other types of atoms are more likely to be dark matter than other hypothetical particles.
The third explanation is that these signals come from previously unknown neutrino properties. These ultra-light elementary particles are ubiquitous and rarely interact with other matter, but occasionally. If they interact with the tweezers in this experiment, the signal indicates that their magnetic moment is larger than described by the standard model of particle physics. This in itself requires new physics to explain it.
The team says solar axes are the frontrunners in terms of possibilities. The statistical significance of this hypothesis is 3.5 sigma, which means that the probability of a two-tenths of a result is random. To this extent, scientists usually need a five-figure meaning to “determine.” The other two assumptions are considered to be slightly less likely, with a significance of 3.2 sigma.
Exactly what was observed in that large underground tank is still a mystery, but an upgraded version of the experiment may have the answer. The next stage, called XENONNT, will have three times the active argon mass of the previous version and should have less background noise.
A preprint of the study has been published on ArXiv.