A curious gap between theoretical predictions and experimental results in a major neutrino research project could be a sign of an elusive “sterile” neutrino – a very quiet particle, detectable only by the silence it leaves in its wake.
This isn’t the first time we’ve seen anomalies, as well as previous experimental data suggesting something strange in the world of neutrino research. This time, it was discovered in the Baksan Experiment on Sterile Transformations (BEST).
Clear evidence of hypothetical sterile neutrinos could provide physicists with a powerful candidate for supplying the mysterious universe with dark matter. On the other hand, this can simply lead to a problem with the models used to describe the strange behaviors of old-school neutrinos.
Which would also constitute an important moment in the history of physics.
“The results are very exciting,” says Los Alamos National Laboratory physicist Steve Elliott.
“This definitely reaffirms the anomalies we’ve seen in previous experiments. But what this means is not clear. There are now conflicting results about sterile neutrinos. If the results point to a misunderstanding of basic nuclear or atomic physics, that would be very interesting, too. “
Despite ranking among the most abundant particles in the universe, neutrinos are known to be difficult to pick up. When you have barely mass, no electric charge, and make your existence known only by the weak nuclear force, it is easy to slip through the densest of matter unimpeded.
The ghost-like motion of the neutrino is not only its intriguing quality. Each particle’s quantum wave morphs as it takes off, oscillating between distinct “flavors” that echo the resonance of negatively charged particles – the electron, muon, and tau.
Studies of neutrino oscillations at the US Los Alamos National Laboratory in the 1990s noted gaps in the timing of this permutation that left room for a fourth flavor, one that would not occur like a ripple in the weak nuclear field.
Hidden in silence, the sterile flavor of neutrinos will only be evident by a brief pause in their interactions.
BEST is protected from cosmic neutrino sources under a mile of rock in the Russian Caucasus Mountains. It features a double-chamber tank of liquid gallium that patiently collects neutrinos emitted from the radioactive chromium core.
After measuring how much gallium has turned into a germanium isotope in each tank, the researchers can work backwards to determine the number of direct collisions with neutrinos as they oscillate through the electron flavor.
Similar to the “gallium anomaly” of the Los Alamos experiment, the researchers accounted for one-fifth to a quarter of germanium less than expected, indicating a deficit in the expected number of electron neutrinos.
This does not mean with certainty that neutrinos briefly adopted a sterile flavour. Many other searches for faintly small particles come up empty-handed, leaving open the possibility that the models used to predict transitions are somewhat misleading.
This is not a bad thing in itself. Corrections to the basic framework of nuclear physics could have major implications, potentially revealing gaps in the Standard Model that could lead to explanations for some of the science’s great remaining mysteries.
If this is indeed a sign of a sterile neutrino, we may finally have evidence of matter in massive amounts, yet it only forms a gravitational canvas in the fabric of space.
Whether this is the sum of dark matter or just a piece of its puzzle depends on further experiments with more ghostly particles.
This research was published in Physics review letters And physical review c.