In a 4,000-meter-long laboratory facility more than a mile below the mountains of the Caucasus in Russia, an experiment involving nearly two dozen metal disks composed of a rare radioisotope revealed an anomaly that could change our understanding of physics.
Although the description above may sound like it comes straight from a scene from The X Files, what it actually describes is the setting for a recent experiment to confirm the possible existence of a new elementary particle: the sterile neutrino.
The Baksan Neutrino Observatory is without a doubt one of the most unusual laboratories in the world. Existing under the gorge of the Baksan River in the Russian Caucasus, construction began in 1977 and is now home to an extensive network of underground facilities that contain an arsenal of technological marvels, including the Baksan Underground Scintillation Telescope (BUST).
Since 2019, the Baksan Sterile Transition Experiment (BEST), a study conducted within a 4,000-meter horizontal tunnel that runs under the slopes of the Andirci Mountains, has also been held here. Extending the tests that began in the 1980s as a joint research effort between the Soviets and the United States to measure solar neutrino flux, BEST researchers spent several years working on new physical insights that could even help shed light on the dark matter. of the greatest mysteries of the universe.
Now, according to a new scientific paper outlining the results of the current experiment, confirmation of an anomaly that has long puzzled physicists could mean that science is approaching confirming the existence of sterile neutrinos. This may point to the possibility of something going wrong with our current understanding of the standard model of physics.
“The results are very exciting,” said Steve Elliott, a lead analyst in the physics department at the Los Alamos National Laboratory, which is collaborating with the BEST experiment.
“This definitely confirms the anomaly we’ve seen in previous experiments,” Elliott said in a statement from the Los Alamos National Laboratory. “But what that means is not obvious.”
At the heart of the mystery lies the sterile neutrino, a still hypothetical particle that physicists recognize as unique – if they exist – because of the way their interactions relate only to gravity, unlike other types of interactions recognized within the standard. model.
It is now known that neutrinos exist in three types: electron, muon and tau. Previous experiments conducted in 2007 at the National Fermi Accelerator Laboratory in Batavia, Illinois, failed to find evidence for a fourth type of neutron. However, the results of the new BEST study may once again shake the foundations of the standard model, thus reviving questions that remain for our understanding of physics.
“There are now conflicting results for sterile neutrinos,” says Elliott. “If the results show that fundamental nuclear or atomic physics are misunderstood, that would also be very interesting.
In a recent study, BEST researchers found that the rate of production of a specific isotope, germanium 71, was found to be almost 25% lower than predicted in the standard model. Germany 71 was produced using a set of 26 disks made from another isotope – chromium 51 – which serves as a reaction point between electronic neutrinos and gallium.
The dual-zone gallium target used in the recent experiment, which is irradiated from a source of electronic neutrinos (Credit: AA Shikhin).
This is important because it aligns with past observations of the anomaly, which researchers first discovered in previous experiments that began in the 1980s. The Soviet-American gallium experiment, or SAGE, also conducted tests with gallium and neutrino sources, which are known to be high-intensity. The SAGE experiments were the first to notice the so-called “gallium anomaly”, recognized again during the last BEST experiments.
Although there is more than one possible explanation for the anomaly, vibration of particles from electronic neutrinos to their hypothetical sterile neutrino states is among the interpretations the researchers have considered. If this is proven to be the cause of gallium deficiency in both experiments, it would be important because sterile neutrinos may be a component of the mysterious dark matter believed to exist in the universe, parts of which may consist of weakly interacting particles.
However, it remains possible to have other interpretations that could better explain the anomaly. Elliott and Los Alamos researchers, who review the best results, note that some of the information currently missing from researchers includes measurements of the electron neutrino cross-section at energies comparable to those in the BEST and SAGE experiments. A possible way to achieve such measurements may include the discovery of another conundrum in physics: the temperamental electron density in the atomic nucleus, which has been proposed as a possible input for measuring the cross section of an electron neutrino.
To reduce the likelihood of error, special attention was paid to the use of counting systems, as well as radiation sources, their location and other elements in the experiment. Yet, given the possibility that some theoretical data may remain in question, it can still prove that there are aspects of physics that work in experiments that will require rethinking.
Looking ahead, BEST may try to replicate the experiment with minor changes that include a different radiation source capable of producing shorter oscillation wavelengths based on the decay rate of the half-life.
If the same observations of “missing” electronic neutrinos appear in future experiments, in contrast to the predicted results according to the standard model of physics, this may indeed indicate the reality of the long-sought sterile neutrino and thus a deeper understanding of the fine mechanics of our universe.
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