Neutrinos have been a real problem for physicists for a long time already, mainly because they are extremely difficult to detect. The vast majority of them, about two thirds, go missing on their way from the Sun to Earth. Now, with refined calculations, physicists realized that we might also have underestimated the number of their antimatter counterparts.
Back in the 1960’s, physicist Ray Davis found that the flux of neutrinos coming from the Sun was only about a third of the amount predicted theoretically. Decades later, in 2001, the mystery was solved when the Sudbury Neutrino Observatory (SNO) in Canada found the missing two-thirds by realizing there are actually three flavors (or types) of the particle: electron, muon and tau. Only the smallest kind, the electron neutrino, had been detected by Davis.
But now, another mystery has appeared. Thierry Lasserre and his colleagues at the French atomic energy commission (CEA) in Saclay, while waiting for the Double Chooz neutrino experiment to be fully operational, checked the predictions for antineutrinos against the actual amount produced by nuclear reactors. The previous calculations were made in the 1980’s, and so far experiments produced results roughly consistent with the theory.
Because they used more modern techniques, the researchers were more precise: they estimated that the rate of production of anitneutrinos is actually 3% more than previously predicted. That is a surprise: if the previous calculations were wrong but the subsequent results correct, this means that several experiments missed a small fraction of the particles!
Then, where are these particles? The answer might lie in a fourth flavor, a so-called sterile version of the particle: in this state, neutrinos and antineutrinos do not interact with ordinary matter.
This might also be the solution to another long-standing problem, that has left researchers in the dark… If they don’t interact with matter, these particles could be the constituent of the susbtance accounting for the Universe’s hidden mass, dark matter (or it could just be part of it). Other experiments, such as the Liquid Scintillator Neutrino Detector at Los Alamos National Laboratory in New Mexico and the Mini Booster Neutrino Experiment, at Fermilab in Batavia, Illinois, have also seen evidence for sterile particles.
Finally, although the result is very interesting, it is not significant on its own. Other experiments with similar observations are needed, and there is still a long way before sterile particles can be proven to exist.
- Mention, G. et al. http://arxiv.org/abs/1101.2755
- Abdurashitov, J. N. et al. http://arxiv.org/abs/nucl-ex/0512041