DOE Scraps Plans for Neutrino Experiment in Mine

The U.S. Department of Energy (DOE) is putting the brakes on the development of a gigantic experiment seen as the flagship project for the next decade at the country's sole particle physics laboratory.

At a projected $1.5 billion, the Long-Baseline Neutrino Experiment (LBNE) at the Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois, is not affordable, says William Brinkman, director of DOE's Office of Science. So this week he asked physicists to come up with a cheaper way to do the same science.

The current plan for LBNE is to build a gigantic particle detector in the abandoned Homestake gold mine in South Dakota. The detector would contain tens of thousands of tons of frigid liquid argon and would snare elusive subatomic particles called neutrinos fired through Earth from Fermilab 1300 kilometers away. The experiment would search for an asymmetry between neutrinos and antineutrinos, called CP violation, which could shed light on why the burgeoning universe developed so much matter and so little antimatter.

But the prospect of flat budgets for years to come puts its cost out of reach. "We do not see that we can afford a project as large as that proposed as LBNE," Brinkman tells ScienceInsider.

Brinkman did not rule out building some type of neutrino detector in Homestake, however. In fact, in a 19 March letter to Fermilab Director Pier Oddone, Brinkman asked Fermilab researchers to come up with alternative plans that might accomplish the same science in more manageable steps. "In order to advance this activity on a sustainable path, I would like Fermilab to lead the development of an affordable and phased approach that will enable important science results at each phase," Brinkman explained.

The slowdown of LBNE is the latest twist in the long saga to build an underground lab in Homestake. For years, scientists had hoped that the National Science Foundation (NSF) would be willing to spend up to $875 million to build a multipurpose lab. That would have included $100 million or more for two smaller experiments to be located there—one to search for particles of the mysterious dark matter whose gravity holds the galaxy together and another to search for a type of radioactive decay that would prove that neutrinos are their own antiparticles. Those efforts would have been preceded by "demo" projects. The lab would have also housed DOE's LBNE. But those plans fell apart in December 2010, when the National Science Board, which sets policy for NSF, declined to continue design work for the lab.

NSF's decision left DOE with the monumentally expensive task of developing Homestake. Many physicists assumed that DOE would forge ahead with only LBNE, which is critical to Fermilab's future, and let the dark-matter and radioactive decay experiments fall by the wayside. Building only the two smaller experiments in Homestake would make little sense, physicists have said, because the mine itself costs tens of millions of dollars a year to operate. (Merely pumping water out of the mine costs $1 million per month.)

Brinkman says DOE is now considering taking the opposite tack and moving ahead with the smaller experiments first. "[W]e are going to keep the mine open and do the demo experiments on dark matter and neutrinoless double beta decay and continue to research how else we can move forward on determining how to measure the CP-violating phases of the neutrinos," Brinkman says.

The stakes are very high for Fermilab, whose plans for the next decade revolve around LBNE. Physicists say they are willing to work with DOE officials to put the neutrino experiment on a more achievable budget and schedule. "I can tell you that we are having conversations on how to stretch out the project to make it more manageable financially," says Milind Diwan, a physicist at DOE's Brookhaven National Laboratory in Upton, New York, and co-spokesperson for the LBNE collaboration.

The project will undergo a review next week at Fermilab, Diwan says, at which point the options may become clearer.