for a deep underground laboratory have included existing but closed mines, new excavation, and operating mines or repositories. The magnitude and scope of these proposals provide both a significant opportunity and a serious challenge: the breadth of the proposals attests to the substantial excitement for the potential science at these major facilities but demands a careful assessment of this potential in the face of the large long-term costs and responsibilities.
The obvious commonality between the two scientific initiatives included in the charge to the committee, IceCube and a deep underground laboratory, is that both explicitly involve neutrinos and both operate below the surface. A more accurate statement is that both deal with research requiring the detection of extremely rare phenomena. However, although neutrinos (or other rare phenomena) play a prominent role in both initiatives, the origins of the neutrinos, their energy range, and the science IceCube and a deep underground laboratory would address are very different. Furthermore, the two initiatives differ substantially in scope. The IceCube project is a specific, dedicated experiment exploiting the clear ice at the South Pole to construct a cubic-kilometer-scale detector for very high energy neutrinos from space. It addresses a variety of astrophysical problems and potential sources of high-energy neutrinos. In contrast, a deep underground laboratory would provide a general facility with attributes essential for a wide variety of important experiments for detecting neutrinos, rare decays, and extremely weak interactions. At this time, the specific experiments that might be conducted at a particular deep underground laboratory location have not been chosen, but the scientific questions they would address are evident.
Organized largely along the lines suggested by the formal charge to the committee, this report outlines some of the general science common to both initiatives and provides some of the historical and international context for subsequent discussions in this report. Second, it identifies the major science potential of the IceCube project and discusses it in the context of other large-volume neutrino observatories. The report then describes the major science potential of a deep, underground national science laboratory, considering it in the context of ongoing international activities in these research areas. Finally, it presents the committee’s conclusions regarding the scientific merit of this research, the unique opportunities and capabilities of these two facilities, and the issue of possible redundancy between the two types of facility.