Atom smashers at work

Posted: Monday, October 27, 2008 10:07 AM by Alan Boyle

CERN A cross-section image of the Compact Muon Solenoid charts the "splash" of particles entering the detector when the Large Hadron Collider's proton beam was steered into a collimating component in the beam line on Sept. 10, during startup.

Europe's Large Hadron Collider is out of order until next year, but that doesn't mean the atom-smashing scientists and engineers behind the world's biggest atom smasher are taking the winter off. Last week, U.S. scientists involved in LHC research gathered at Fermilab, just outside Chicago, to talk about what has to be done between now and next spring - and what they expect to do once the collider is open for business again.

Friday's first-ever meeting of the US-LHC Users Organization gave scores of researchers an opportunity to hear what their colleagues on experimental teams were doing, share practical tips for working at the site on the French-Swiss border, and commiserate over the electrical mishap that forced a shutdown of the LHC just days after its much-celebrated startup on Sept. 10.

The European Organization for Nuclear Research, known by its French acronym CERN, has provided bits and pieces of information about the mishap, which began with a faulty electrical connection between magnets in the collider's underground tunnel and opened up a serious breach in the helium cooling system.

Eric Prebys, director of the U.S. LHC Accelerator Research Program, provided more of the story: "The damage was actually profound in the tunnel," he told the Fermilab audience.

Although pictures of the damage have not been released, Prebys noted that the cylindrical magnet systems were jolted by up to 20 inches (50 centimeters). Some of the magnets were ripped from their moorings. CERN has said that, at most, 29 of the magnets will have to be repaired, but it may be difficult to assess the full scope of what has to be done until the entire 17-mile-round (27-kilometer-round) ring system is checked out.

"The effort that's being mounted is just heroic," Prebys said.

The first of the magnet systems to be repaired are due to be brought up to the surface this week, Prebys said. "We're still planning for beam on May 1 or thereabouts," he said.

Taking it slow
The accident occurred during a test to see if the magnet system could handle the electrical load required to accelerate the LHC's twin proton beams to energies of 5 trillion electron volts, or 5 TeV. When the collider is brought back online, CERN may set a slower ramp-up schedule to reach the full energy of 7 TeV per beam, Prebys said.

"It would surprise me personally if they go to 7 TeV in the first year," he said.

In the meantime, experimenters are calibrating their detectors using cosmic-ray hits, and finding minor problems that need fixing. On the ATLAS detector, for example, some of the detector elements "are not working well," said Brookhaven National Laboratory's Howard Gordon, U.S. ATLAS deputy research program manager.

"This is going to get fixed, and we're working on it," he said.

The other major detectors - the Compact Muon Solenoid (a.k.a. CMS), ALICE and LHCb - will be ready to go as well, team representatives said.

To-do list for discoveries
So what will scientists see once the machine is turned on again? They told me that they don't expect to make major discoveries during the first runs. The initial collisions will be used to confirm what researchers have already found out from earlier particle-physics experiments.

"Yesterday's discoveries are the calibrations of today," said the University of Maryland's Nicholas Hadley, U.S. CMS collaboration board chairman.

Those calibrations will take time. "We'd be happy if we can get that part finished in a year," Hadley said. Then researchers will push out into the unknown.

Gordon said the LHC's detectors could find evidence of microscopic black holes and extra dimensions within the first year or two - if they exist. (Scientists say the black holes would be harmless, even in the unlikely event that they're created at the LHC.)

Solutions to another set of mysteries, having to do with supersymmetric particles and dark matter, could also come to light "in the first stage" of the experiment, Gordon said. However, the evidence for supersymmetry would come in the form of missing energy after a collision. That means scientists will have to make doubly sure that there are no faults or "blind spots" in the detector systems.

One of the LHC's main goals is to detect the Higgs boson, sometimes called the "God Particle" because it is thought to play a central role in creating the property of particle mass. Scientists say no one should expect the Higgs to turn up in the first year's observations. "The Higgs is going to take a little bit longer, I believe," Gordon said.

The Americans who are working on the LHC are proud of the fact that a billion TV viewers tuned in for last month's startup, beating out Britney Spears on the buzz-o-meter. But now that the hype is fading, will the public be patient during the potentially long wait for discoveries?

"We would be much better off if we had our discoveries very soon," Hadley acknowledged. "We know this."

Other findings from Fermilab:

• There's been less talk lately about the race between the LHC and Fermilab's Tevatron collider to detect the Higgs boson. "It'd be great if they find the Higgs at the Tevatron," Gordon said magnanimously, "but the window of opportunity at the Tevatron is really small compared with the huge opportunity at the LHC." The Tevatron's quest to find the Higgs is the subject of "The Atom Smashers," a documentary airing next month on PBS.
  
  
• Federal support for another big science project, the ITER experimental fusion reactor, has has been in limbo ever since Congress slashed the Energy Department's budget request last December. (The word at the meeting was that the office of Rep. Peter Visclosky, D-Ind., chairman of the House Energy and Water Development Appropriations Subcommittee, played a role in the opposition to ITER funding.) Officials said the likeliest scenario for giving the U.S. ITER effort a boost would be a supplemental appropriation early next year - replaying the way things turned out during fiscal year 2008.
  
  
• How will science policy change after next month's presidential election? "Energy, climate - these things may change significantly. Physics probably won't," said Jean Cottam, assistant director for the physical sciences and engineering at the White House's Office of Science and Technology Policy. Cottam said the Bush administration has kept tabs on the LHC. "It actually came up at a senior staff meeting at the White House," she said, although the main topic of conversation was doomsday black holes.

For more about the LHC, check out our special report on "The Big Bang Machine."

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