The mystery of the vanishing neutrinos

Massive...but tiny

Physicists have confirmed enigmatic sub-atomic neutrino particles do indeed have mass. Seemingly paradoxially, the MINOS experiment at the huge underground Fermilab accelerator in Illinois corroborated the fact by showing that they disappear.

The multinational team sent a high-intensity beam of neutrinos from Fermilab through 450 miles of solid rock to the Soudan detector in a former Minnesota iron mine. Neutrinos are so small and weakly interacting they can pass through the entire planet uninterfered with.

The scientists say that if their neutrinos had no mass, long thought to be a strong possibility, they would have detected around 180 interactions. Instead, just 92 were observed. UK-based Keith Mason, CEO of PPARC, said: "The MINOS experiment is a hugely important step in our quest to understand neutrinos."

The MINOS finding is consistent with neutrino oscillation explanation of the particle's odd properties.

Under this hypothesis, muon neutrinos, the type beamed out by the Fermilab emitter switch into one of the other two flavours; electron neutrinos and tao neutrinos. It's called oscillation because the changes can work back and forth.

Things get pretty weird in the quantum world.

Once emitted a muon neutrino will become a mixture of two, or all three, flavours as it sails along. For the maths of this explanation to work the different forms must have different, and therefore non-zero, masses.

So the MINOS team's vanishing muon neutrinos fit in nicely with this and indicate neutrinos do have a mass. Et voila! Easy-peasy.

The study puts lots of...ahem...weight behind neutrino oscillation by repeating work done in Japan at a similar Big Science operation.

Neutrinos are a hot ticket in particle physics research. Boffins are currently constructing the Rik Waller of detectors at the South Pole from a cubic kilometre of ice to investigate neutrinos from outside the Solar Sytem. ®

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