ROGER DIXON gestures, bringing his hand alarmingly close to the big red button that has the power to shut down one of the world’s most powerful particle accelerators forever. “It’s already hooked up,” he says, in response to my nervous questions.
We are standing in a room full of blinking displays and control panels at Fermi National Laboratory (Fermilab), which nestles among cornfields outside Chicago. Dixon, who is in charge of the smooth running of the accelerator, the Tevatron, pulls his hand back.
Once king, the Tevatron is due to shut down on 30 September as it can no longer compete with the energies achieved by the Large Hadron Collider (LHC) at CERN near Geneva, Switzerland. “It is being superseded,” admits Fermilab director Pier Oddone…..
For years, Fermilab hoped the Tevatron would find the Higgs boson, the particle thought to endow all others with mass. It has not, and that task has now passed to the LHC. Instead the Tevatron will likely be remembered most for its discovery in 1995 of the top quark, the last of the six quarks in the standard model of particle physics to be seen. But just as the Higgs spotlight moves away from Fermilab, another, potentially equally exciting particle may thrust the lab into the limelight again.
Last week, the OPERA experiment rocked the foundations of physics when it reported subatomic particles called neutrinos apparently breaking the light-speed barrier (see “‘Light-speed’ neutrinos point to new physical reality”). As it turns out, Fermilab’s existing neutrino experiment, MINOS, is well suited to confirming or ruling out this bizarre observation. MINOS fires neutrino beams of an energy similar to those detected at OPERA to a detector in the Soudan mine, 800 kilometres away in Minnesota.
Its first task will be to update a 2007 search for faster-than-light neutrinos, which didn’t throw up anything statistically significant, using more recent data. That could be completed in six months, says MINOS collaborator Jenny Thomas of University College London. Meanwhile, the next incarnation, MINOS Plus, will have new GPS sensors, atomic clocks and detectors to record neutrino arrival time with a precision of 2 nanoseconds. This could deliver results as early as 2014.
In the absence of the Tevatron, neutrino physics will soon receive the bulk of Fermilab’s resources, and focus on more than pure speed. A short drive from the Tevatron control room is a symbol of this shift – a black, brick-shaped structure the size of a school bus. It is part of the Nova experiment, which will begin in 2013.
Nova will study neutrinos’ ability to morph, or “oscillate”, from one type to another, looking for potential differences in the way neutrinos and their antimatter counterparts oscillate, which MINOS results hint at. In the early universe, the differences might have created a preponderance of matter over antimatter that would account for the universe’s current composition.
“Neutrinos have been a source of big surprises in the past,” says Oddone. “I don’t think we’re going to understand particle physics until we understand neutrinos.”
Fermilab might yet come back with an accelerator to rival the LHC. In a brightly lit laboratory with gleaming white floors, I glimpse what looks like a stack of silver doughnuts. Made of pure niobium, this bumpy tube will be superconducting when chilled to near absolute zero in a bath of liquid helium. If 16,000 tubes can be lined end to end, they will form an accelerator called the International Linear Collider. The electrons and positrons it smashes together will have a collision energy of 1 teraelectronvolt. That’s a fraction of the LHC’s 7 TeV, but if the LHC discovers the Higgs, say, the ILC should be able to measure its mass and other properties more precisely.
As the Tevatron’s last day approaches, few here seem sentimental. Fermilab helped make the Tevatron obsolete, after all, by building some of the LHC’s magnets and contributing to one of its two main detectors. “It’s a bittersweet moment,” says Oddone. “It has been quite a wonderful life for the Tevatron. But you don’t stay at the leading edge unless you build new things.”