Washington

It's not just distance that separates the two neutrino projects planned by the United States — their scientific objectives are clearly different too, according to a review by the National Academy of Sciences.

The report was commissioned earlier this year by the White House Office of Science and Technology Policy (OSTP) to clarify the degree of overlap between the proposed IceCube neutrino detector in Antarctica and the National Underground Science Laboratory (NUSL), which would probably be built at Lead, South Dakota (see Nature 417, 5; 200210.1038/417005b).

The academy panel was chaired by Barry Barish, a physicist at the California Institute of Technology in Pasadena. This month's report describes the two projects as distinct, saying that there is “essentially no overlap or redundancy in their primary science goals”.

John Marburger, director of the OSTP, says that although the report confirms the projects are scientifically distinct, they will end up competing for money in any case.

Neutrinos are subatomic particles with no electric charge and very small mass. They seldom interact with other particles and are not deflected by electromagnetic fields, so they can travel unhindered through turbulent regions of space. “Recent discoveries have created special opportunities to use neutrinos in new ways to advance our knowledge of the Universe and the laws that govern it,” the panel finds.

Simulation: strings of light-sensitive detectors in IceCube, one of two proposed neutrino projects. Credit: DARWIN RIANTO & BILL BELLON

The planned projects both aim to detect these elusive particles, but from different sources and for different reasons. IceCube would monitor a cubic-kilometre block of Antarctic ice for the rare flashes of light that occur when neutrinos interact with water molecules. The sheer size of IceCube means that it should detect neutrinos generated by powerful events outside our Galaxy, giving astrophysicists a new way to observe phenomena such as black holes. The neutrinos might also shed light on other high-energy particles that inhabit intergalactic space.

By contrast, the NUSL, a laboratory that would have facilities 2–4.5 km below ground, would study the properties of neutrinos generated closer to home — by the Sun and by particle accelerators on Earth. Its experiments would be aimed at improving researchers' understanding of neutrinos themselves and of the fundamental nature of matter.

But despite their differences, the two projects have some things in common: each is projected to cost about a quarter of a billion dollars to build, and each has already lined up some enthusiastic backers in Congress. IceCube, for example, secured $15 million in funding in 2002 and could receive another $25 million next year (see Nature 418, 573; 200210.1038/418573a).

But the panel's sterling endorsement of both projects is no guarantee that either will proceed. The National Science Foundation and Department of Energy will now review the findings and decide whether to include them in future budget requests.