A surprising discrepancy between theoretical expectations and practical results in a major neutrino project might be a clue of the elusive'sterile' neutrino — a particle so silent that it can only be discovered by the silence it leaves behind.
It's not the first time the anomaly has been noticed, and it adds to a growing body of experimental evidence pointing to something unusual in neutrino studies. It was discovered this time during the Baksan Experiment on Sterile Transitions (BEST).
The existence of unambiguous evidence for the hypothetical sterile neutrino might give scientists with a strong contender for the Universe's unexplained dark matter source. On the other hand, it might all boil down to a flaw in the models used to explain old school neutrinos' peculiar behaviour.
This would also be a watershed point in the history of physics.
"The results are very exciting," says physicist Steve Elliott of the Los Alamos National Laboratory.
"This definitely reaffirms the anomaly we've seen in previous experiments. But what this means is not obvious. There are now conflicting results about sterile neutrinos. If the results indicate fundamental nuclear or atomic physics are misunderstood, that would be very interesting, too."
Neutrinos are notoriously difficult to catch, despite being one of the most plentiful particles in the Universe. It's easy to slide through even the densest of materials unnoticed when you have no mass, no electric charge, and only make your existence known by the weak nuclear force.
The ghost-like mobility of the neutrino isn't its only intriguing feature. The quantum wave of each particle transforms as it travels, bouncing between distinct 'flavors' that resemble those of its negatively charged cousins, the electron, muon, and tau.
In the 1990s, researchers at the US Los Alamos National Laboratory discovered gaps in the timing of this flip-flopping that allowed for a fourth flavor to emerge, one that wouldn't even cause a ripple in the weak nuclear field.
The sterile flavor of neutrino would only be discernible by a brief halt in its interactions if it were hidden in silence.
Under a mile of granite in Russia's Caucasus Mountains, BEST is sheltered from cosmic neutrino sources. It has a double-chambered liquid gallium tank that carefully gathers neutrinos emerging from a chromium core that has been irradiated.
The researchers could work backwards from the number of direct contacts with neutrinos while they were cycling through their electron flavor by analyzing the quantity of gallium that had changed into a germanium isotope in each tank.
Researchers computed a fifth to a quarter less germanium than predicted, implying a shortfall in the expected quantity of electron neutrinos, similar to the Los Alamos experiment's own 'gallium anomaly.'
This isn't to suggest that the neutrinos had taken on a sterile taste for a limited period of time. Many additional searches for the pale tiny particle have turned up empty-handed, raising the likelihood that the models used to forecast the changes are deceptive on some level.
This isn't always a negative thing. Corrections to nuclear physics' basic framework might have far-reaching implications, identifying flaws in the Standard Model that could lead to answers to some of science's biggest unsolved riddles.
If this is the sterile neutrino's mark, we may finally have proof of a substance that exists in vast amounts but merely produces a gravitational dent in the fabric of space.
Further investigation on the most ghostliest of ghost particles will determine if this is the total of dark matter or only a piece of its jigsaw.
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