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Experiment catches shifty neutrinos

minos.jpg A particle physics experiment based at Fermilab announced results Friday afternoon that provide yet more evidence of rare neutrino oscillations — evidence that can help explain why matter in the Universe dominates over anti-matter.

The result is consistent with evidence presented just 10 days ago by a complementary Japanese neutrino experiment, which also found that the pervasive, ghostly particles can shift, or oscillate, between three different flavours: tau neutrinos, muon neutrinos and electron neutrinos. The fact that the neutrinos oscillate is evidence that they have mass, and is also important in explaining the matter-anti-matter asymmetry in the Universe. The two experiments are the first to have started with a beam of muon neutrinos and, at a detector many miles away, to have found a tiny extra number of electron neutrinos — evidence that some of the muon neutrinos had morphed into electron neutrinos.

They both shoot the neutrinos along long underground paths, which increases the chances of rare oscillations. In the case of the Fermilab experiment, called the Main Injector Neutrino Oscillation Search, or MINOS, the neutrinos were shot from the Fermilab campus, in Batavia, Illinois, to a mine in Soudan, Minnesota — a distance of 735 kilometres (see picture).

The Japanese experiment, called Tokai to Kamioka, or T2K, sends neutrinos on a 295 kilometre path. Because of the damage from the April earthquake, the experiment has had to temporarily stop taking data.

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