Alec Aivazis edited Introduction.tex  almost 10 years ago

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In 1934, When the parts of the standard model were first being pieced together, Enrico Fermi introduced a particle called a neutrino that is fermionic in nature and does not ineract with baryonic matter, in order to explain how beta decay could convserve fundamental quantities (energy, spin, etc.) \cite{Wilson_1968} . For awhile, only electron neutrinos were thought to exist. However, fifty years later in 1988, Lederman, Schwartz, and Steinberger earned the Nobel Prize in physics for work they did in 1962 at the Alternating Gradient Synchotron at the Brookhaven National Laboratory. In their paper, the group from Columbia reported that they had found a second kind of neutrino that did not couple to the electron like the one proposed by Fermi, but instead to muons produced by their beam in upstate New York \cite{Danby_1962} . Another forty years passed before the third generation of neutrino was dicovered in 2000 by the DONUT collaboration at Fermilab near Chicago, Illinois \cite{Kodama_2001} .  \subsection{Neutrino Oscillations}  In 1958, Bruno Pontecorvo, an assistant of Enrico Fermi, suggested that if neutrinos did in fact have a mass (unlike what Fermi suggested) then the neutrinos we encounter might be a particle mixture of more fundamental mass states. Consequently, Pontecorvo argued, there is some probability of transitioning between neutrino and its associated anti-neutrino. (CITE PONTECORVO PAPER Sov.Phys.JETP 7 (1958) 172-173 ). Around the same time, a variety of experiments reported a discrepancy between the measured the measured number of neutrinos created in solar rays and what they expected. Coupled with the discovery of the muon neutrino, Pontecorvo accredited this so-called "solar neutrino problem" to the oscillation of neutrinos between various flavor states due to a non zero mass. In 1967, he wrote that "from the point of view of detection possibilities ... if the oscillation length is much smaller than the radius of the solar region which effectively produces neutrinos ... it will be impossible to detect directly oscillations of the solar neutrino [by current technology]." He continues to say that "the only effect at the surface of the earth would consist in the fact that the flux of observable solar neutrinos would be half as large as the total flux of solar neutrinos" \cite{PONTECORVO_1968}