Arguments for a “US Kamioka”: SNOLab and its implications for North American underground science planning

Abstract

We argue for a cost-effective, long-term North American underground science strategy based on partnership with Canada, initial construction of a modest US Stage I laboratory designed to complement SNOLab, and follow-up stages to create clean horizontal access to greater depths. We show, by reviewing the requirements of detectors now in the R&D phase, that SNOLab and a properly designed US Stage I facility would be capable of meeting most needs of North America's next wave of underground experiments. One opportunity for creating such a laboratory is the Pioneer tunnel in Washington State, a site that could be developed to provide dedicated, clean, horizontal access. This unused tunnel, part of the deepest (1040 m) tunnel system in the US, would allow the US to establish, at low risk and modest cost, a laboratory at a depth ( 2.12 km .w.e., or kilometers of water equivalent) quite similar to that of the Japanese laboratory Kamioka ( 2.04 km .w.e.). The site's infrastructure includes highway and rail access to the portal, a gravity drainage system, redundant power, proximity to a major metropolitan area, and a system of crosscuts connecting to the parallel Great Cascade tunnel and its ventilation system. We describe studies of cosmic ray attenuation important to properly locating such a laboratory, and the tunnel improvements that would be required to produce an optimal Stage I facility. We describe the unique role this location could play in formulating an international plan for high-energy accelerator physics that includes, as one component, a neutrino factory. The site has a “doubly magic” baseline—a 7500 km separation from both KEK and CERN—as well as an appropriate baseline for CP violation studies, should FermiLab host the neutrino factory. We also describe how new space at greater depth could be added in response to the needs of future experiments, building on the experience gained in Stage I. We discuss possible designs for Stage II ( 3.62 km .w.e.) and Stage III ( 5.00 km .w.e.) developments at the Pioneer tunnel, should future North American needs for deep space exceed those available at SNOLab. This staging could be planned to avoid duplication of SNOLab's capabilities while minimizing construction and operations costs. We describe the existing geotechnical record important to future stages, including past tunneling histories, borehole studies and analyses, and recent examinations of the Pioneer tunnel. We also describe the significant broader impacts of this project in improving the efficiency, safety, and security of one of the nation's key transportation corridors.