Friday, January 13, 2006

Neutrinos and Me

I did my Ph.D thesis on a search for neutrino oscillations. Neutrino oscillations are a quantum mechanical phenomena where a neutrino is produced as one type but after it has traveled some distance it observed to be another type. In my thesis experiment we used a beam of neutrinos produced at the CERN PS that was almost purely muon neutrinos. We then looked for electron neutrinos in our detector. We found four of them, but that was also what we calculated to the
impurity of the beam, so nobody won a Nobel prize, but I still got my Ph.D in 1986.

Neutrinos were finally obcserved to oscillate by the Super K experiment in 1998.In this case muon neutrinos were produced by cosmic rays striking the atmosphere. Super K found that the number of muon neutrinos that came from the far side of the earth was smaller than those that came from directly overhead. If you do not know about neutrinos you might think that makes sense, but it turns out that very few neutrinos get stopped by the earth. Super K was able to look many different angles between straight up and straight down, which means the neutrinos went different distances through the earth. The pattern of neutrinos obcerved by angle was consistent with the muon neutrinos oscillating into tau neutrinos which are not recognized by the detector.

However, this oscillation was not of the type that I searched for so many years ago. That oscillation has still not been found. Two different groups hope to see that oscillation. One in the US called NOvA and one in Japan called T2K. These experiements are being planned and will use beams of neutrinosfrom accelerators and put detectors that are hundreds of kilometers
away.

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