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The atoms out of which all normal matter is built are in turn made up of smaller pieces: protons and neutrons, made from quarks; and electrons, the commonest lepton.. Neutrinos are also a kind of lepton; they're the very lightweight partners of the electrically charged electron and its more exotic cousins the muon and the tau. (Physicists use the word flavor to describe these three different kinds of lepton; that is, leptons come in electron flavor (electrons and electron neutrinos), muon flavor (muons and muon neutrinos), and tau flavor (taus and tau neutrinos).) Since neutrinos are neutral, they don't feel the electromagnetic force; since they're leptons, they don't feel the strong force. This makes them a useful "weak force only" probe of particle interactions. It was always thought that neutrinos were massless, but some recent experiments have cast doubt on that assumption. The MiniBooNE experiment will delve more deeply into this crucial question of neutrino mass. So... How do you weigh a neutrino? It turns out that neutrino mass and the strange phenomenon of neutrino oscillations are deeply linked; if neutrinos oscillate, then they must have mass. When neutrinos oscillate, they switch flavors, a phenomenon that violates a Standard Model commandment that a neutrino that starts out as one flavor stays that way forever. (This is sometimes called lepton number conservation.) MiniBooNE will start with a beam of 100% pure muon neutrinos, and then look downstream to see if it can find evidence of other flavors (electron or tau). MiniBooNE at Fermilab is scheduled to begin a two-year run in 2002, and is currently completing the construction of its detector and beam line. MiniBooNE's search for the oscillation of muon neutrinos into electron neutrinos will test the results of an earlier experiment, the Liquid Scintillator Neutrino Detector (LSND) experiment at the Los Alamos National Laboratory. LSND was the first experiment to report an appearance of electron neutrinos from a muon neutrino source. MiniBooNE will search for neutrino oscillations with parameters in and around the region in which LSND reports to have detected a signal. Finding oscillations would further our understanding of the LSND result and enable the parameters of this sort of oscillation to be more precisely determined. If no oscillations are observed, MiniBooNE will extend the excluded region for neutrino oscillations. |