Large Hadron Collider Now Back on Line After Two-Year Break

The Large Hadron Collider (LHC), the largest and most powerful particle accelerator ever built, is back in operation. On April 5, Sunday, Rolf Heuer, the director-general of CERN, the European Organization for Nuclear Research, announced: "Operating accelerators for the benefit of the physics community is what CERN's here for. Today, CERN's heart beats once more to the rhythm of the LHC."

The CERN in its press statement last Sunday reported: "Today at 10.41 am, a proton beam was back in the 27-kilometer ring, followed at 12.27 pm by a second beam rotating in the opposite direction. These beams circulated at their injection energy of 450 GeV. Over the coming days, operators will check all systems before increasing energy of the beams."

The LHC was built from 1998 to 2008 in collaboration with over 10,000 scientists and engineers from all over the world. It lies in a tunnel 27 kilometers in circumference, as deep as 175 meters beneath the Franco-Swiss border near Geneva, Switzerland. It is designed to collide two opposing particle beams of either protons at up to 4 teraelectonvolts (TeV), with energies to be increased to around 6.5 TeV in 2015. The LHC first went live on September 10, 2008. After the end of the 2012-2013 run, the LHC went into shutdown for upgrades to increase beam energy to the target 6.5 TeV per beam for this year's experiments.

Physicists hope that the revamped LHC will help find some new physics beyond the standard model, the existing paradigm of particles and forces. The Higgs boson, discovered at the LHC in 2012, was the last missing piece of the standard model, but the theory does not include a host of things physicists know exist, such as dark matter and gravity. Quoting Marumi Kado, a particle physicist who works on the ATLAS project, one of the detectors on the LHC's loop which collects data from the particle collisions, Newsweek wrote: "We don't have a coherent, complete model [of physics] that includes gravity. The standard model does not explain it. We don't have a quantum theory of gravity. So we believe there is something that could lead us forwards to better integrate gravity."