During the last several years, stunning experimental results have established that neutrinos have nonzero masses and substantial mixing. The Standard Model must be extended to accommodate neutrino mass terms. The observation that neutrino masses and mass splittings are all many orders of magnitude smaller than those of any of the other fundamental fermions suggests radically new physics, perhaps originating at the GUT or Planck Scale, or perhaps the existence of new spatial dimensions. In some sense we know that the Standard Model is broken, but we don't know how it is broken. Whatever the origin of the observed neutrino masses and mixing, it is likely to require a profound extension to our picture of the physical world. The first steps in understanding this revolutionary new physics are to pin down the measurable parameters and to address the next round of basic questions: (1) Are there only three neutrino flavors, or do light, sterile neutrinos exist? (2) If there are only three generations, there is one angle ({theta}{sub 13}) in the mixing matrix that is unmeasured. How large is it? (3) Which of the two possible orderings of the neutrino mass eigenstates applies? (4) If {theta}{sub 13} is large enough onemore » it may be possible to measure the quantum-mechanical phase {delta}. If {theta}{sub 13} and {delta} are non-zero there will be CP violation in the lepton sector. These questions can be addressed by accelerator based neutrino oscillation experiments. The answers will guide our understanding of what lies beyond the Standard Model, and whether the new physics provides an explanation for the baryon asymmetry of the Universe (via leptogenesis), or provides deep insight into the connection between quark and lepton properties (via Grand Unified Theories), or perhaps leads to an understanding of one of the most profound questions in physics: Why are there three generations of quarks and leptons? The answers may well further challenge our picture of the physical world, and will certainly have important implications for our understanding of cosmology and the evolution of the early Universe. The current Fermilab Program is an important part of the world-wide accelerator based effort to explore and understand the physics of neutrino oscillations. By early 2005, with both MINOS and MiniBooNE taking data, Fermilab will be able to answer some of the most pressing first-round questions raised by the discovery that neutrinos have mass. Fermilab's high-intensity neutrino beams are derived from 8- and 120-GeV proton beams. MiniBooNE is currently taking data using 8 GeV Protons from the Booster. The 120 GeV NuMI beam will start to operate in early 2005 using a 0.25 MW proton beam power from the Main Injector. Future neutrino programs will build on these existing facilities. New short and long baseline experiments have been proposed. There are proposals to increase the available number of protons at 8 and 120 GeV with the goal of addressing the full range of questions presented by neutrino oscillations. Key to that vision is a new intense proton source that usually is referred to as the Proton Driver.« less
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Jul 1, 2024
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