Rebooting the Large Hadron Collider in Search of Dark Matter

The Large Hadron Collider, at the European particle physics laboratory in Geneva, on July 23, 2014. Pierre Albouy/Reuters

Scientists are eagerly preparing for "Season 2" of the most powerful particle accelerator in the world. During its first run, the Large Hadron Collider (LHC) at CERN, the European Organization for Nuclear Research, was instrumental in the discovery of the Higgs boson. After a two-year shutdown, during which the machine was undergoing maintenance and improvements, researchers are working to get it powered back up, this time with nearly twice the energy.

"When you look around, you might not see, but we are all already excited," said CERN General Director Rolf Heuer at a press briefing Thursday. "We are entering a new phase after two years of heavy improvement," he explained, and the goal is to perform a "stringent test of our standard model" of physics. "It's high time to find a crack," he says, considering 95 percent of the universe is still unknown.

The LHC, which Science magazine dubs an "atom smasher," is located near Geneva, Switzerland. The accelerator "pushes protons or ions to near the speed of light," according to a CERN fact sheet. "It consists of a 27-kilometer [about 17-mile] ring of superconducting magnets with a number of accelerating structures that boost the energy of the particles along the way."

In 2012, the LHC allowed researchers to find the Higgs boson, a long-hypothesized quantum particle and the key to physicists' theory about how other fundamental particles get their mass. The particle is part of the standard model of physics, which Guy Wilkinson, a spokesman for the LHCb experiment, one of the seven experimentation programs at the LHC, calls "a highly successful but incomplete theory that describes nature."

François Englert and Peter W. Higgs won the 2013 Nobel Prize in physics "for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle by the ATLAS and CMS experiments at CERN's Large Hadron Collider." Science named the Higgs boson its 2012 breakthrough of the year.

But many questions remain unanswered, says Dave Charlton, spokesman for the ATLAS experiment. For example, "what is dark matter? Can we re-create and study it in the laboratory?" The answers may take scientists beyond the standard model of particle physics.

"Until now we have not found things like dark matter or other evidence of new particles that go beyond [the] standard model," says Tiziano Camporesi, spokesman for the CMS experiment. "If you want to produce a new state of matter," he explains, "you need to have the energy to produce it.... The secret is having enough energy." That's why in the LHC's second run, the researchers will be increasing the energy applied to the particles from eight tera electron volts to 13.

"We are basically breaking a new energy domain," says CERN Director of Accelerators Frédérick Bordry, which will "open up [the] possibility of a new state of matter never detected before. This is the machine that is at the frontier of what can be done in terms of fundamental searches."

Since the LHC began its first shutdown, in early 2013, it has undergone extensive inspection and improvement to prepare for its upcoming run at higher energy levels, so much so that it's "almost a new machine," Bordry says. The connections between magnets have all been inspected, Heuer explains, with about a third redone and all of them reinforced to ensure they can remain stable.

CERN published a video Thursday describing the work done on the LHC during the two-year shutdown:

As for the timeline for the LHC's "Season 2 premiere," Bordry told those tuning in for the press briefing to remember that restarting the most powerful particle accelerator ever built is not like flipping a switch on a phone. In other words, he can't tell you the exact moment when it goes from off to on; it's a process. The researchers have already introduced the first proton beams into the machine over the weekend to test how they move through the collider, which Bordry says went well.

You have to be "very careful in switching on such high power," Heuer explains—each beam could melt 500 kilograms (over 1,000 pounds) of copper. "And actually we don't want to do that," he says, joking. Instead, the researchers will start by producing small-scale collisions and increase the intensity and power of the beams step by step, until they are ready to introduce two full-powered beams at once. "Our estimate is roughly two months," Heuer says. "Hopefully, around the end of May we'll get the first [full-energy] collisions."

In the longer term, Heuer says, the plan is to continue operating the LHC through roughly 2035 on a similar schedule: three years running, followed by one to two years off for maintenance. Throughout the next two decades, the researchers hope to increase the energy of the beams and the collision rate per second.

"One thing I can guarantee to you: There will be fantastic results," says Heuer. "What kind of discoveries? I don't know. When? I don't know. But we're doing fantastic science."