It's been closed for renovations and upgrades since 2013, but on Sunday, the Large Hadron Collider powered on with no sign of complications, and successfully carried two proton beams, fired in opposite directions, around its 27km circumference.

Above: The New and Improved LHC, with numerical callouts designating the particle accelerator's upgrades - click to enlarge. Via CERN: 1) New magnets 2) Stronger connections 3) Safer magnets 4) Higher energy beams 5) Narrower beams 6) Smaller but closer proton packets 7) Higher voltage 8) Superior cryogenics 9) Radiation-resistant electronics 10) More secure vacuum | Image Credit: Dominguez, Daniel; Brice, Maximilien; De Melis, Cinzia

“After two years of effort, the LHC is in great shape,” CERN Director for Accelerators and Technology, Frédérick Bordry, said of the particle accelerator's recent upgrades, in a statement. “But the most important step is still to come when we increase the energy of the beams to new record levels.”

Sunday's beams circulated at a relatively tame injection energy of 450 GeV, but the LHC is now equipped to operate at an energy of 6.5 TeV per beam (nearly double the per-beam maximum prior to 2013's shutdown. If things go according to plan, CERN scientists say they'll be conducting 13 TeV proton-proton collisions before summer:

The Brout-Englert-Higgs mechanism, dark matter, antimatter and quark-gluon plasma are all on the menu for LHC season 2. After the discovery of the Higgs boson in 2012 by the ATLAS and CMS collaborations, physicists will be putting the Standard Model of particle physics to its most stringent test yet, searching for new physics beyond this well-established theory describing particles and their interactions.The LHC’s second run began with the introduction of a proton beam into the 17-mile ring. A short while afterward, a second beam, traveling opposite the first, was introduced. These two beams will continue to circulate; by summer CERN staff hope to double the beams’ energy being to the output of its first run. By summer, scientists hope to start colliding beams.

More via CERN and BBC.

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