Several experiments conducted since the 1990s to study neutrinos have discovered something very strange: Far too many particles hit the detectors. In particle physics, scientists are excited about even small deviations from the expected experimental results. Now, a new experiment conducted deep underground more than two kilometers below Russia’s Caucasus Mountains has confirmed the previously observed anomaly, pointing to an as-yet-unconfirmed new elementary particle dubbed the “sterile neutrino.” It’s either that our physics is flawed, so these results are incredibly consistent no matter the outcome.
Sterile neutrinos deep underground
neutrinos Nature’s most abundant particles, perhaps second only to photons, are the particles of light. You don’t see them, but they are everywhere. About a trillion neutrinos pass through your hand every second. Most come from the sun, while others are generated in the upper atmosphere when gases are struck by cosmic rays from supernovas and other space events.
There are three known types or flavors of neutrinos: electron, muon, and tau neutrinos. But many scientists believe there is a fourth flavor lingering in the shadows, waiting for its rightful place with its particle family. Tentatively termed sterile neutrinos, if they exist, they could help solve quite a few lingering mysteries in physics, such as why neutrinos have mass when in theory they should be massless like photons. Sterile neutrinos – so named because they are believed to interact with other particles solely through gravity, while the other three flavors also do so through weak force – may also explain the nature of dark matter, the invisible and elusive matter that makes up 85% of all matter. matter in the universe, even though we can’t measure it directly.
Researchers associated with the Baksan Experiment on Sterile Transitions (BEST), including US researchers at Los Alamos National Laboratory, used irradiated disks of chromium 51 (a synthetic radioisotope of chromium) and a powerful source of electron neutrinos to paint the inside and outside parts of a tank made of gallium to be irradiated. As a result of this reaction, the experiment produced the isotope germanium 71.
That was totally to be expected, but what was abnormal was that the production rate was 20-24% lower than the theory suggested. The methodology of the experiment is believed to be flawless, and furthermore, the discrepancy is in the same margin that was recorded by other previous experiments.
“The results are very exciting,” said Steve Elliott, principal analyst for one of the teams evaluating the data and a member of the Los Alamos physics division. “This definitely confirms the anomaly we’ve seen in previous experiments. But what this means is not clear. There are conflicting results now about sterile neutrinos. If the results show that fundamental nuclear or atomic physics is being misunderstood, so would be.” be very interesting.”
One of the earlier experiments with similar results was the predecessor to BEST, a solar neutrino experiment from the 1980s, the Soviet-American Gallium Experiment (SAGE), which also used gallium and a high-intensity neutrino source. Both BEST and SAGE were conducted thousands of feet below the entrance to a tunnel at the Baksan Neutrino Observatory, located in the Baksan River gorge in Russia’s Caucasus Mountains.
Neutrino detectors are generally buried deep underground to protect them from interference from cosmic rays and other radiation that would harm the experiment if the detectors were exposed on the surface. A next-generation neutrino detector called the Deep Underground Neutrino Experiment, or DUNE, is currently being built 48 kilometers (30 miles) underground at the Fermi National Accelerator Laboratory in Batavia, Illinois. When finished, it will be able to shoot bundles of neutrinos through the Earth’s mantle.
Did we miss dark matter because our understanding of physics is flawed?
There are many reasons why physicists love neutrinos. They provide a direct connection between us and the Sun’s core, allowing scientists to look into nuclear fusion processes without having to place detectors in space. But perhaps the most intriguing thing about neutrinos is that they oscillate between flavors, like a chameleon changing color in response to its environment. For example, a particle that starts out as an electron neutrino can turn into a tau or muon neutrino and vice versa.
Gaps in the timing of these oscillations recorded by the experiment in Russia, and other similar experiments before it, suggest that there is a fourth flavor that we are missing. This hypothetical particle may also very well be a major component of dark matter.
But that does not mean that a fourth type of elementary particle is the only explanation. The results of the experiment also raise the intriguing possibility that our current theoretical framework describing neutrinos is flawed. That wouldn’t be bad news at all. Science is a constant work in progress, always replenishing the status quo with new, compelling evidence. In the process, the institution of science becomes stronger and more credible, and better equipped to answer increasingly complex questions about nature.
The findings appeared in the Physical Assessment Letters†
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