Researchers have begun circulating beams of protons in the Large Hadron Collider after a two-year shutdown for upgrades — and they expect to ramp up quickly to reach uncharted frontiers in particle physics.
"Beam went smoothly through the whole machine. It's fantastic to see it going so well after two years and such a major overhaul of the LHC," Rolf Heuer, the director general of Europe's CERN particle physics center, said Sunday in a statement.
The LHC's control team sent waves of protons in both directions around the 17-mile-round (27-kilometer-round) ring, situated 300 feet (100 meters) beneath the French-Swiss border near Geneva. In the days ahead, the team will increase the energy of the proton beams and smash them together in the LHC's detectors.
The LHC is the world's most powerful collider. It's also the most expensive, with an estimated construction cost of $10 billion. Thousands of physicists and engineers are on its experimental teams.
During its first research run, between 2009 and 2013, the collider was used to discover the Higgs boson, a subatomic particle whose existence was predicted in the 1960s but could not be detected until the LHC came along. The Higgs is thought to play a role in imparting the property of mass to other fundamental particles — and it was the last big missing puzzle piece in the Standard Model, the theory that governs particle physics.
The LHC accelerates protons to nearly the speed of light, using a ring of powerful magnets that have been cooled down to nearly absolute zero. The interconnections between the magnets were upgraded during the shutdown to handle increased power levels. One of the magnets experienced an intermittent short circuit about a week ago, but engineers were able to fix the glitch quickly and get the magnets "trained" for Sunday's restart.
During its first run, the LHC's collisions hit a top energy of 8 trillion electron volts, or 8 TeV. This time around, they're due to rise to 13 TeV, close to the machine's maximum design level.
"The only question in everybody's mind is, 'Can you crank it up to higher energies?' ... That's the biggest jump in energy we're going to have during my lifetime," said Joe Lykken, a theoretical physicist at Fermilab in Illinois.
Cosmic rays in outer space can get much more powerful than 13 TeV, but physicists have never before been able to study such energetic collisions under controlled conditions on Earth. "The basic thing we're looking for is to start producing some new heavy particles that we couldn't produce last time," Lykken said.
The LHC could point the way to new scientific frontiers — perhaps extra dimensions of space, or new fundamental forces of nature, or the constituents of dark matter, or a whole new array of previously undetected supersymmetric particles. The first hints of such frontiers could conceivably emerge within a couple of months, physicists say.
"Our best possible scenario is that we see supersymmetry, we see extra dimensions, we see evidence of dark matter, and it's all tied together in some new theory that blows our mind," Lykken said. Some reports have even suggested the LHC will open a portal to parallel universes, but Fermilab physicist Don Lincoln said such claims were "depressingly bogus."
Even if minds aren't completely blown, Run 2 is certain to provide an opportunity to learn more about the elusive Higgs boson. And the LHC is still just getting started: Future upgrades are expected to boost the machine's performance even higher between now and its scheduled retirement in 2035.