Tuesday, April 05, 2011

The Neglected Neutrinos

... or in this case, the uncounted for antineutrinos, but not on purpose.

It seems that neutrinos are still missing in one form or another. A new calculation has reported that we may have underestimated, by roughly 3%, the amount of antineutrinos generated out of nuclear power plants.

Experiments that measure the rate of antineutrino production from the decay of uranium and plutonium isotopes have so far produced results roughly consistent with this theory. But the revised calculation1 accepted this week by Physical Review D suggests that it's not the whole story. While waiting for the Double Chooz neutrino experiment in France to become fully operational, Thierry Lasserre and his colleagues at the French atomic energy commission(CEA) in Saclay set out to check predictions of the rate of antineutrino production by nuclear reactors. They repeated a calculation first done in the 1980s by Klaus Schreckenbach at the Technical University of Munich, using more modern techniques that allowed them to be much more precise.

Their new estimate of the rate of production is around 3% more than previously predicted. This means that several generations of neutrino and antineutrino experiments have unknowingly missed a small fraction of the particles. "It was completely a surprise for us," says Lasserre.

A possible mechanism for the non-detection of these antineutrinos could be the possible oscillation into "sterile" neutrinos.

The result may be pointing to evidence of neutrinos and antineutrinos oscillating into a fourth kind of neutrino or antineutrino, a so-called 'sterile' version that doesn't interact with ordinary matter, says Carlo Giunti, a physicist at the University of Turin in Italy. Other experiments have previously seen evidence for sterile particles, including the Liquid Scintillator Neutrino Detector at Los Alamos National Laboratory in New Mexico and the Mini Booster Neutrino Experiment, or MiniBooNE, at Fermilab in Batavia, Illinois, and the search to confirm their existence is a hot area of physics.

With several neutrino experiments going online soon, one would think that this would be something that might looked at. So stay tuned!


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