If a nuclear reactor produces a beam of just one type of neutrino, theory predicts that some should change their identity as they travel to a far-off detector
Analyzing more than 300,000 electron antineutrinos (the antimatter counterpart of the electron neutrino) collected from the Daya Bay nuclear reactors during 217 days of operation, Daya Bay's measurement of antineutrino flux—the total number of antineutrinos emitted across the entire energy range—indicates that the reactors are producing 6 percent fewer antineutrinos overall when compared to some of the model-based predictions.
One explanation for the deficit is that some of the electron antineutrinos have transformed into an undetectable, lightweight sterile neutrino, about one-millionth the mass of an electron. Another Examples:
the Liquid Scintillator Neutrino Detector(Los Alamos National Laboratory) in New Mexico from 1993 to 1998.
called MiniBooNE, at Fermilab, ran from 2002 to 2012
a second strange feature — an excess of electron antineutrinos (compared with theoretical predictions) at an energy(~5MeV). That could be a sign of completely new physics awaiting discovery (or simply that scientists don't have a detailed enough grasp of the output of nuclear reactors).
Impacts:
If a light sterile neutrino exists, it might have siblings about 1,000 times heavier which could contribute to the as-yet-unidentified dark matter.
Sterile neutrinos, more than a times heavier than the electron, could explain an ever bigger cosmic mystery — the mismatch between the amounts of matter and antimatter in the cosmos.