UPDATE: Restarted LHC Sees First Collisions

November 23, 2009

After more than a year of repairs, the Large Hadron Collider (LHC) is now a step closer to simulating post-big bang conditions: Physicists have smashed together protons traveling at nearly the speed of light for the first time inside the world's largest particle accelerator.

The collision occurred at relatively low energy—900 billion electron volts (GeV), with each beam supplying 450 GeV. The much anticipated event came only three days after physicists began circulating the first beam of protons inside the LHC's main 17-mile (27-kilometer) ring.

"Things are really moving extraordinarily fast," said Dan Green, a particle physicist at the Fermi National Accelerator Laboratory in Illinois and a member of the LHC's Compact Muon Solenoid experiment. "I wasn't expecting it when I came in this morning."

The next stage will be to accelerate the beams to 1.2 teraelectron volts (TeV) each—the highest energy level yet achieved by any particle accelerator—and collide their protons. This is expected to occur sometime in the next few days before a planned winter break.

When LHC operations resume again in January 2010, physicists will further ramp up the beams' energy levels until they eventually reach the collider's full potential of seven TeV per beam.

Happy Bunch of Physicists

Earlier this morning, LHC operators had established a stable counterclockwise beam, which joined a clockwise beam that had been established last Friday in the doughnut-shaped main ring of the so-called big bang machine.

The successful LHC reboot and first collisions come after extensive repairs due to an electrical short circuit that sparked heavy damages to the collider last September.

Minor glitches since the halted startup have fueled growing speculation, even among scientists, that the machine is fated to fail.

But now the Large Hadron Collider is "doing extremely well," said Paul Collier, head of the beams department at the European Organization for Nuclear Research (CERN), which operates the LHC.

"We've spent a year tinkering with the machine, correcting all the faults to make sure the problem won't happen again," Collier said, adding that the control room team is now filled with relief and excitement.

"We're all a fairly happy bunch."

Large Hadron Collider's Full Potential

The LHC's high-energy particle collisions are designed to re-create the conditions that existed in the universe right after the big bang, helping scientists better understand the origins of the universe and how it developed into what we see today.

The LHC could also confirm the existence of the theoretical Higgs boson, sometimes called the God particle, which could help explain the origin of mass in the universe.

But keeping the beams moving and steering the protons toward collisions requires careful control of thousands of magnets chilled to a temperature colder than outer space.

On September 10, 2008, Large Hadron Collider operators had successfully fired the first beams of protons around the collider. But within weeks an electrical glitch caused tons of supercooled helium to leak into parts of the machine's tunnels.

While repairs were underway, scientists used the downtime to calibrate their detectors and fine-tune their software.

"The LHC is a far better understood machine than it was a year ago," CERN's director for accelerators, Steve Myers, said in a statement.

"We've learned from our experience and engineered the technology that allows us to move on. That's how progress is made."

So far, the CERN team has been very cautious as it ramps up toward full power—and that's a good thing, said Fermilab's Green.

Even if caution means that it takes a while for experiments to start, Green said, "I've been in this business for more than 20 years. I can wait a little longer."

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