Physics News

Neutrinos have mass:

Neutrinos are hard to detect, and most of the neutrinos traveling the 450 miles from Fermilab to Soudan–straight through the earth, no tunnel needed–leave no signal in the MINOS detector. If neutrinos had no mass, the particles would not change as they traverse the Earth and the MINOS detector in Soudan would have recorded 177 +/- 11 muon neutrinos. Instead, the MINOS collaboration found only 92 muon neutrino events–a clear observation of muon neutrino disappearance and hence neutrino mass. The deficit as a function of energy is consistent with the hypothesis of neutrino oscilations and yields a value of delta m2, the square of the mass difference between two different types of neutrinos, equal to 0.0031 eV2 +/- 0.0006 eV2 (statistical uncertainty) +/- 0.0001 eV2 (systematic uncertainty). In this scenario, muon neutrinos can transform into electron neutrinos or tau neutrinos, but alternative models–such as neutrino decay and extra dimensions–are not yet excluded. It will take the recording of much more data by the MINOS collaboration to test more precisely the exact nature of the disappearance process.

Oh dark matter, where art thou?


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