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Big bang machine revs up again

Workers walk around the ATLAS detector's calorimeter during the Large Hadron Collider's winter maintenance period. The LHC's proton beams were restarted over the weekend.
Workers walk around the ATLAS detector's calorimeter during the Large Hadron Collider's winter maintenance period. The LHC's proton beams were restarted over the weekend.Claudia Marcelloni / CERN

After a winter maintenance break, Europe's Large Hadron Collider went back into operation this weekend, beginning a marathon that scientists hope will lead to theory-twisting breakthroughs.

Argonne National Laboratory's Thomas LeCompte, who is physics coordinator for the LHC's ATLAS detector, said the particle accelerator resumed shooting proton beams around its 17-mile-round (27-kilometer-round) underground ring on Saturday night. James Gillies, a spokesman for Europe's CERN nuclear research center, told me that proton-on-proton collisions could resume within a week.

During the next two years, the underground particle accelerator could produce data pointing to the nature of dark matter, or the discovery of a whole new class of unanticipated subatomic curiosities, or the existence of extra dimensions ... or the presence of the Higgs boson, the so-called "God Particle" that could explain why some particles have mass and others don't.

"By the end of next year, we hope very much that we will be able to say something about the Higgs," said Felicitas Pauss, head of international relations at Europe's CERN nuclear research center.

String theory supported

Researchers are already able to say something about potentially new physics, coming out of just a few weeks' worth of lead-ion collisions in November. Those collisions created quark-gluon plasma, an exotic type of matter that existed just an instant after the big bang, said Yves Schutz, a CERN physicist who is part of the team behind the LHC's ALICE detector.

"We have produced in the laboratory the hottest matter ever, the densest matter ever," Schutz said today during a session at the American Association for the Advancement of Science's annual meeting in Washington.

Previous experiments conducted at another particle accelerator, the Relativistic Heavy-Ion Collider in New York, showed that quark-gluon plasma took on the form of a liquid. Some scientists expected the plasma to go to a gaseous state at the higher temperatures achieved by ALICE, but it didn't. Instead, it was a "perfect liquid, which flows without resistance and is completely opaque," Schutz said.

That in itself was a big surprise. But Schutz told me that the results were consistent with what had been predicted by a particular variant of string theory known as AdS/CFT correspondence, which also addresses such mysteries as quantum gravity and extra dimensions. "I'm surprised that they can make a prediction and that it matches what we measured," Schutz said.

String theory is a long-debated conception of the subatomic world that envisions matter as being composed of incredibly tiny strings or membranes that vibrate in an 11-dimensional universe. Skeptics have criticized the concept as being untestable and unfalsifiable, but if findings from the LHC can confirm some hypotheses and falsify others, that could increase string theory's acceptance.

Only the beginning

The collider is scheduled to run at its current energy of 3.5 trillion electron volts (TeV) per beam for 2011 and 2012, with a weeks-long maintenance break next winter that would be similar to the break that has just ended. At the end of 2012, the machine would be shut down for more than a year to get it ready to run at its full power of 7 TeV per beam.

Over the past year, the LHC's beams have been at 3.5 TeV, producing results that have confirmed decades' worth of findings from earlier particle accelerators. But the collisions have not yet yielded enough data to provide evidence for the exotic theories that scientists have suggested, Pauss said. LeCompte explained that the telltale signs of dark matter, microscopic black holes, supersymmetric particles or the Higgs boson are so rare that scientists have to search through huge amounts of data to find them — and then make sure that the evidence is rock-solid.

He compared the task to an oil-prospecting operation. "You might strike oil, but you haven't explored the whole field," LeCompte said.

By the end of 2012, scientists should have enough data to confirm or reject claims about the Higgs boson and the other oddities. If the Higgs is not found, that might force physicists to take a second look at the Standard Model, the theory of subatomic structure that ranks as one of physics' biggest achievements.

"We know the Standard Model is wrong at some level," LeCompte said. "We know that something lies beyond that. The Higgs is the simplest and most elegant way to push it to the next level, but nature may have something else in mind."

A good number of scientists say failing to find the Higgs boson at the LHC would actually be more intriguing than finding it — even though they admit it'd be hard to tell that to the politicians who have funded the $10 billion international project.

"If we don't see it, we will be very excited, because it means that there's something very brand-new," the University of Maryland's Nicholas Hadley, who is a member of the research team for the LHC's Compact Muon Solenoid detector, told journalists at today's news briefing. "But to say we looked and we didn't find anything ... we'll probably volunteer to have other people stand up here in front of you if that day comes."

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