CERN scientists ramp up to restart collider

The Large Hadron Collider at CERN, nagged by overruns and delays, may solve a few mysteries – and pose many more – when it restarts on Feb. 15 and ramps up to unprecedented levels of speed.

By , Staff writer

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    High impact: The Compact Muon Solenoid is one of two behemoth detectors that track the particles created when two beams of protons are smashed together at nearly the speed of light.
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Working on the cutting edge of science is a tough job.

Just ask Stephen Myers. He's the director of accelerators and technology at the European Organization for Nuclear Research (CERN), the continent's premier high-energy physics lab.

CERN was criticized for cost overruns during the construction of its crown jewel, the $4.5 billion Large Hadron Collider (LHC). Since its completion, technical delays have prevented the LHC from doing what it was designed to do: create high-energy collisions among tiny particles to help physicists answer some of the deepest remaining mysteries about the universe.

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In September 2008, the collider ran for only a few days before it had to be shut down for major repairs. In November 2009, the 17-mile loop deep beneath the Swiss Alps was restarted and scientists recorded collisions at the highest energy levels humans had yet achieved. It was then shut down for winter.

Now, Dr. Myers is eyeing the payoff for a 15-year project dubbed the single most expensive scientific experiment in history.

On Feb. 15, the collider will start up again. Soon thereafter, it will start producing scientific data for the first time. This year, the plan is to ramp up the collider to unprecedented levels of speed in order to test traditional physics theories. If all goes well, Myers expects the LHC to run at full energy – accelerating particles to nearly the speed of light – in 2011.

The year-end run for the collider went more smoothly than many expected. But, says Myers, "For us, it's still just scratching the surface."

"From a purely scientific point of view, new results are months away," adds Thomas LeCompte, physics coordinator for ATLAS, one of two cathedral-scale detectors along the LHC's 17-mile circumference.

Energy levels of 13.8 billion years ago

Bringing the LHC to the eve of delivering its first scientific results has been a bit like tending a newborn child, Dr. LeCompte says. When one arrives, "it takes a lot of effort, makes a lot of noise, and doesn't produce much. But there's potential there, and everybody's really excited."

The excitement stems from the LHC's mission – to probe matter at energy levels thought to have existed just after the big bang some 13.8 billion years ago. At LHC energies, the universe was only a 10-billionth of a second old and unimaginably hot.

The collider aims to create those energies by accelerating two beams of protons in opposite directions to 99.9 percent of the speed of light. Researchers then steer the beams into head-on collisions. Detectors track the debris the collisions generate. High-powered supercomputers pick through the debris trails in hopes of spotting the signature of the hypothesized particle that imparts mass to matter, the Higgs Boson. They will also look for particles that make up so-called dark matter (the vast majority of matter in the universe), and particles that may hint at the presence of other dimensions beyond the four we can sense.

"Dark matter" was given its name because it rarely interacts with ordinary matter. Learning more about it may open the door to more mysteries.

"It's plausible that dark matter may be part of some broader story where we have more particles which are visible and are related to dark matter," says Steven Giddings, a physicist from the University of California at Santa Barbara who also works here at CERN. These partner particles, if they exist, would decay into less energetic particles after being created by a collision. Physicists could then work backward to calculate the properties of these partner particles. From those efforts they could infer the properties of dark-matter particles.

Another approach will be to see if particles generated as collision debris recoil from dark-matter particles, says LeCompte. Because you still wouldn't see dark matter directly, he notes, it's a bit like the clue Sherlock Holmes found in the dog that didn't bark.

Dr. Giddings says their research may bolster the case for supersymmetry – a concept in physics that would lead physicists toward a long-held goal: an ability to explain the four forces of nature in terms of quantum physics. That could lead to showing that the basic forces of nature today are low-energy manifestations of one unified force that briefly held sway during the universe's earliest moments. So far, researchers have been able to develop and test quantum explanations for three of the four forces. Gravity remains the holdout.

Other experiments will probe other questions, including: "Why are we here?" When the universe burst from the big bang, according to current scientific theories, it should have created equal amounts of matter and antimatter, which would have annihilated each other. Yet enough matter survived to give us the universe we see today. Researchers at CERN will hunt for an explanation.

Until last December, the most powerful collider on the planet had top impact energies of 2 trillion electron volts (TeV), a unit that describe a particle's energy of motion. On a macro scale, 2 TeV is roughly like mosquitoes colliding. But at the subatomic level it's a big-time particle buster.

Testing standard-model predictions

When the LHC operates at full tilt, its collisions will reach energies of 14 TeV. Initially, planners anticipated achieving that in early 2011, after a six-month maintenance shutdown scheduled for next winter. But at a meeting last week, CERN officials opted to run at the 7 TeV energy for the next 18 to 24 months. The facility would enter a planned shutdown in the fall of 2011 to prepare for running at the design energy, then aim for 14 TeV once that shutdown ends.

Getting there will be a gradual process. Step 1 is to bring the machine up to a collision energy of 7 TeV while increasing the number of protons racing around the underground ring. Although 7 TeV is half the LHC's maximum, it should generate interesting science, says Marjorie Shapiro, a physicist at the Lawrence-Berkeley National Laboratory in Berkeley, Calif.

The so-called standard model of particle physics, which describes the properties and functions of a zoo of subatomic particles discovered so far, makes predictions for particle behavior that will now be tested, Dr. Shapiro says.

The lower-intensity tests also will serve to establish the background "noise" against which anything truly new must be spotted.

"With new physics, the effects start out as subtle," Shapiro says. And no one will believe results pointing to "new physics" if the LHC doesn't get the standard physics right, she cautions.

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