Plans to build a gigantic underground lab in the United States may be in limbo. But the science that would be done there has received a stamp of approval from an expert panel convened by the National Academies.
Today's report declares that the three major experiments physicists hope to build in the abandoned Homestake gold mine in the Black Hills of South Dakota are of "paramount scientific importance." Although the National Science Foundation (NSF), which requested the study, has since pulled out of the project to convert Homestake into a lab, officials at the Department of Energy (DOE) will find the report useful if they try to salvage parts of the project, which last month a different panel estimated would cost between $1.2 billion and $2.2 billion. "I think they were looking for independent confirmation of the importance of the science," says Andrew Lankford, a physicist at the University of California, Irvine, who chaired the National Academies' committee that issued the report. Responsibility for pursuing the project fell into DOE's lap last December, when NSF abruptly ended its efforts to develop Homestake into an $875 million multipurpose Deep Underground Science and Engineering Laboratory (DUSEL).
Physicists hope to build a trio of exquisitely sensitive particle physics experiments 1480 meters down, where the overlying stone would block out most of the radiation from cosmic rays. The biggest would be a particle detector weighing as much as 200,000 tons to snare wispy particles called neutrinos fired from the Fermi National Accelerator Laboratory (Fermilab) 1300 kilometers away in Batavia, Illinois. Known as the Long-Baseline Neutrino Experiment (LBNE), the detector would look for subtle difference between the behavior of neutrinos and antineutrinos that could ultimately explain why the universe contains so much matter and so little antimatter.
The second largest experiment would be a detector weighing up to tens of tons that would try to detect particles of mysterious "dark matter" floating through space. Some form of dark matter must provide the gravity that binds the galaxies, many astrophysicists think. In fact, the universe appears to contain five times as much dark matter as ordinary matter. The third experiment would search for a hypothesized form of radioactivity called neutrinoless double beta decay. It can only occur if, bizarrely, the neutrino is its own antiparticle. Seeing the decay would also help explain the matter-antimatter imbalance in the universe.
"[E]ach of these experiments is essential and could radically transform scientific understanding and progress," says the report, which emphasizes that the experiments are of "comparable" importance. That assessment seems aimed at discouraging DOE to push ahead with LBNE alone. LBNE is central to plans for Fermilab, which will shut down its 25-year-old atom smasher, the Tevatron, later this year. Without LBNE, the future of the lab and particle physics on U.S. soil may be in jeopardy, many researchers say.
Just crafting the report turned into an adventure for Lankford and colleagues. In 2009, the National Science Board (NSB), which sets policy for NSF, requested a study of the scientific case for DUSEL. Then in December 2010, before the committee had met for the first time, NSB declined to continue funding of the DUSEL development, objecting in part to the cost sharing arrangement by which NSF would spend $480 million on infrastructure while DOE built the biggest experiment in the lab.
That left the committee analyzing an outdated plan. "The change in circumstances led to a lot of thrashing on our part as to whether or not we still had a role and what that role was," Lankford says. But since the agencies still wanted the report, he says, the committee focused on the scientific value of the experiments rather than on the merits of the now-moot DUSEL design.
Of course, the quality of the physics has never really been in dispute. The real question was always whether the federal government--first NSF and now DOE--can afford the project. DOE's current annual budget for particle physics of $795 million would likely have to increase significantly to build even LBNE in a timely manner.