Restarting the world's largest particle accelerator after a two-year overhaul isn't just a matter of throwing a switch and making sure the lights go on. It's an eight-week process of baby steps – one's that involve billions of electron volts. But the Large Hadron Collider (LHC) took a major step forward this week as the CERN team fired up two counter-rotating proton beams that were injected into the LHC using the Super Proton Synchrotron, then accelerated to an energy of 450 GeV each.
During the power up, the 27-km (16.7-mi) ring generated low-energy proton-proton collisions that sent subatomic particles to the ALICE, ATLAS, CMS, and LHCb detector experiments. According to CERN, the purpose of the power up at 9:30 am CET on Tuesday was to help scientists and engineers properly adjust the accelerator and tune the detectors, so they can handle the 6.5 TeV beams that will produce 13 TeV collisions.
As the particles cascaded through the layers of the detectors and subdetectors, the CERN teams monitored them and adjusted the equipment, systems and algorithms, to ensure the subdetectors fire at the precise place and time a particle passes. The idea is that by using these banks of detectors, scientists can reconstruct what happens when the protons collide and from that, learn more about their make up. It's a bit like slamming two pocket watches together and trying to figure out how they work by watching the gears fly out.
According to CERN, the testing by the LHC Operations team will take a total of eight week to make sure that the beams circulate properly and the collider can be recommissioned. This involves testing the many subsystems and fine tuning hundreds of electromagnets. Once this is accomplished, the team can begin to work up to full-power high-energy collisions.
CERN physicists discuss the potential new physics the LHC's "second season" could shed light on in the video below.