In this report, the science that requires instrumenting a very large volume of ice deep under Earth’s surface with photodetectors is assessed. The goal of such exploratory experiments is to open the neutrino window on the universe and to elucidate the origin and acceleration of nature’s highest-energy particles. High-energy neutrinos provide a unique probe into understanding the acceleration mechanisms from astrophysical objects such as active galactic nuclei and gamma-ray bursts that could produce such particles. Detecting these neutrinos is particularly attractive because they reach Earth without absorption and can therefore give insight into their sources and production mechanisms.
The second class of experiments assessed are those that might be placed in a new deep underground laboratory. In recent years, experiments performed below the surface of Earth have received more and more worldwide attention in nuclear physics, particle physics, and cosmic-ray physics, as well as astrophysics and cosmology. Such laboratories, shielded from cosmic rays, allow the study of rare phenomena and provide a window onto the unraveling of some of the most fundamental questions in physics and astrophysics today. The dramatic discoveries of neutrino oscillations (and mass) are a direct result of such experiments, and future deep underground experiments could be key to unraveling some of the most fundamental questions in physics and astronomy. Since the committee finds that the scientific goals of an underground laboratory go well beyond neutrino experiments, it has assessed the scientific potential for such a facility in a broader context.
In addition to providing a scientific assessment of IceCube and of a deep underground laboratory, the committee addresses their overlaps and complementarity, as well as how each initiative fits into international plans. Finally, the committee emphasizes that this report is consistent with, and should be viewed within the context of, the broader planning for future projects in physics and astronomy. In particular, the National Research Council report Connecting Quarks with the Cosmos: Eleven Science Questions for the New Century (National Academies Press, Washington, D.C., 2003) identifies a set of important questions at the interface of astronomy and physics, several of which would be addressed by these projects. By their nature, these two projects are interdisciplinary and bridge traditionally separate disciplines. The recent Department of Energy/National Science Foundation long-range plans for nuclear physics and particle physics also endorse these projects. The DOE/NSF plans find IceCube and a deep underground laboratory to be important projects within the context of the scientific goals and priorities of nuclear and particle physics.