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Neutrinos, the mysterious particle

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(( ---- What is a Neutrino?
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What is a neutrino and how is it possible that it could travel faster than the speed of light?

A neutrino is one of the particles that according to our best theory of Nature (called the Standard Model) is elementary, that is, fundamental. There are three kinds of neutrinos. They have zero electric charge, and very small mass. We do not know exactly their masses, but we know they are not zero and the heaviest neutrino mass is roughly 10^-8 the mass of the electron. Neutrinos are produced naturally in radioactive decays (a banana produce about one neutrino per hour), in the sun, and by cosmic rays. They can also be produced in reactors and accelerators.

Can it travel faster than light? Well, according to the Standard model, it cannot. Yet, like anything else in physics, the question is not what the theory predicts but what we see in experiments. The reason we are very skeptical about the new result is the fact that it seems to contradict a lot of other results. In particular, there is one result that measure the neutrinos that came from a far away source, a supernova. A supernova is an event when a star dies. It is a big explosion that emit a lot of light and neutrinos. in 1987 there was a supernova called SN1987A, and we were able to see the light and detect the neutrinos from it. Because the neutrinos arrive almost at the same time as the light we know that neutrino travel very close to the speed of light. If the new claim from CERN is correct, these neutrinos should have arrived in 1983!

A neutrino is an elementary particle that is emitted in certain nuclear reactions, such as beta-decay (a form of radioactivity) or in reactions in particle accelerators. It reacts extremely weakly with matter: about 1 light-year of lead is required to stop a typical neutrino.

According to special relativity, only massless particles can travel at the speed of light. Neutrinos have a very tiny mass, so we expect their speed to be very close...


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