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Europe's LHC to Run at Half-Energy, Tightening Race for Higgs
2 February 2010 5:37 pm
The world’s highest energy atom smasher, the Large Hadron Collider (LHC), will run at half its maximum energy through 2011 and likely not at all in 2012. Officials at the European particle physics laboratory, CERN, had previously planned to run the gargantuan accelerator at 70% of maximum energy this year.
The change raises hopes at the LHC’s lower-energy rival, the Tevatron Collider at Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois, of being extended through 2012 instead of being shut down next year. Fermilab researchers are hoping that their machine might collect enough data to beat the LHC to the discovery of the long-sought Higgs boson, a particle key to how physicists explain the origin of mass.
The $5.5 billion LHC is designed to blast protons into other protons at an energy of 14 trillion electron-volts (TeV), seven times the Tevatron’s maximum. But it cannot run at full energy because of a few faulty electrical connections, or “interconnects,” between the thousands of superconducting magnets that guide particles around the 27-kilometer subterranean ring. In September 2008, just 9 days after it first circulated particles, the LHC suffered a catastrophic breakdown when an interconnect between two magnets melted. That problem took 14 months to correct. The previous plan was to run the LHC briefly at 7 TeV, stop for a few months to rework the weakest interconnects, then ramp up 10 TeV later this year. CERN officials have now scaled back the energy to 7 TeV for this year and next, says Steve Myers, director of accelerators and technology at CERN.
The new plan balances safety with the desire to collect data, Myers says. CERN officials say they will run at 7 TeV until experimenters collect enough data—1 inverse femtobarn, in the units they use—to give them a shot at, for example, discovering the new particle predicted by a theory called supersymmetry. The LHC would then shut down for a year so workers could replace all of the 10,000 interconnects with redesigned ones, allowing the LHC to run at 14 TeV in 2013. “By doing it this way, we have the time needed to design the new interconnects in a thorough way and make sure it’s done correctly,” says Myers.
CERN experimenters say the good news is that 1 inverse femtobarn of data set would let them search for supersymmetric particles and, even, the new dimensions of space predicted by some version of string theory. “Clearly we would have preferred to run at a higher energy,” says CERN Guido Tonelli, spokesperson for the 3800–member team working a particle detector called the Compact Muon Solenoid. But “this is a real physics run in which we will be able to tackle a large part of our research program.”
Meanwhile, their counterparts at Fermilab are reacting with caution. “It’s not like we’re rushing out and saying ‘We want to run [the Tevatron] in 2012!’ But we want to keep the possibility open,” says Fermilab’s Dmitri Denisov, co-spokesperson for the 510–member team working with Fermilab’s D0 particle detector. One extra year would only increase the size of the D0 data set slightly, from a projected 12 inverse femtobarns to about 15 inverse femtobarns, he notes. That increase alone might not be enough to justify the expense, Denisov says. It would be a different matter, he says, if Fermilab researchers were seeing hints of a Higgs boson that a little extra data might strengthen. A decision on running the Tevatron in 2012 won't have to be made for several months.