A detector designed to hunt dark matter made physical observation particles that I hope to help physicists establish important truths about our universe. No, this is not a dark matter point, but the new result proves that these ultra sensitive detectors are valuable for scientists for many reasons.
Gravity, the universe behaves as if it contains much more material than astronomers have actually identified, so physicists have built experiments to look for candidates for the so-called dark matter. The search for the darkest material candidate has so far become empty.
But one of those dark matter experiments, called XENON1T, is now floating in a process that avoids multiple detection attempts, which scientists hope will better understand the clear particles called the neutrinos.
"It proves that this XENON detector technology we use for dark matter is much more versatile," said graduate student Christian Wittweg, a doctoral student at the University of Münster in Germany, said Gizmodo. "We get all these cool analyzes … free after we've built an experiment sensitive enough to look for dark matter."
Scientists are quite confident that the second most abundant particle in the universe (after photons, light particles) is the neutrino. But neutrinos are very difficult to detect and measure.
We know they have a lot, but we do not know how many. We know they have anti-particles, a kind of bad twin that causes the two particles to destroy if they meet, but do not know the nature of that particle. There is a ton of neutrino mysteries to solve.
The new measurement, called "two neutrino double electron capture", is an important stepping stone to provide these answers.
Two neutrino double electron capture is the most rare particle interaction that was first theory in 1955 and "has escaped for decades", according to an article published in Nature.
In this process, two protons in the nuclear nucleus spontaneously absorb a pair of electrons that surround the nucleus and release a pair of neutrinos. The experimental signature of the event is a volley of x-rays and electrons emanating from other electrons surrounding the atom and replacing the two that are absorbed by the nucleus.
And when I say rare, I mean rare. The average amount of time that will take half of the xenon atoms in the sample to pass the reaction is 1.8 × 1022 years, according to the newspaper. It is about a trillion times the age of the universe.
XENON1T is a well-equipped experiment to measure the rare event. First, it contains a crapload of xenon atoms – an equal 3.2 tonnes of liquid xenon (though, as a button, the xenon isotope used for this measurement constitutes only a small fraction of the total xenon atoms).
Second, the entire installation is buried deep inside the Italian mountain, shielding it from almost any particle that can cause a false signal.
Finally, scientists understand more or less all the noise that can produce a signal in an experiment, thus increasing their confidence by actually finding something important when an abnormal signal appears.
After 214 days of observation (177 days of usable data), an analysis of the researchers revealed approximately 126 events in two double neutrons for electron capture.
This is an amazing scientific achievement. "This is the longest half of life measured directly," says doctoral student Chiara Capelli of the University of Zurich, who works on XENON. Gizmodo.
The researchers do not call their results "discovery" because their statistics do not hit the standard five standard threshold physicists require in order to use the word. Instead, they call it "observation", since the result was significant of 4.4 sigma.
That is, there is only one out of a few hundred thousand chances that they will see this result if the reaction did not exist – but it will take a little more observation to reach the 1.5 million chances required by physicists to notify discovery.
Scientists will then hunt for double electron capture of neutrinos, or neutrinos, an even more rare event where, after the electron's double neutrino event, two neutrinos collide and gamma rays fall. This will prove that neutrinos are their particles, and will allow scientists to put a number to the mass of neutrinos.
It is also a free search for a reaction called neutrinos double beta decay – a kind of opposite of dual-electron neutrinos, where two spontaneous neutrons simultaneously become protons, emitting electrons and a pair of neutrinos that destroy each other.
We do not know if these "neutrino" reactions really happen, but this is an important question for particle physicists. If neutrinos are really their particles, it will help explain why neutrinos are so low, and perhaps the reason why there is so much more substance than an anti-global substance in the universe.
In the end, the scientists need more time to observe. Xenon will soon upgrade to XENONNT with even more liquid xenon, which will allow scientists to observe these events more frequently and to observe longer-lived neutrino events, explained Laura Baudis, a professor of physics at the University of Zurich.
But most importantly, it is proof that these experiments are sensitive enough that they can make other important measurements beyond just looking for dark matter.