Inside CERN's Large Hadron Collider

Scientists at the CERN particle physics center at the French-Swiss borders are preparing to restart the Large Hadron Collider, (LHC), the world's most powerful particle-smasher. Photographer Luca Locatelli was given acces to maintenance work in November, providing a unique view into this vast underground laboratory. Engineers work on equipment for the LHC in the main workshop at CERN shown here.

A model of the Large Hadron Collider is displayed inside the LHC Magnet facility building, where components for the particle accelerator are built. The LHC was first started up in 2008 and is resuming high-energy collisions in March.

The LHC's 17-mile-round underground tunnel directs particles through ATLAS, one of the facility's two general-purpose detectors. ATLAS and the other detector, the Compact Muon Solenoid, probe a wide range of scientific mysteries, from the successful search for the Higgs boson to the hunt for extra dimensions and particles that could make up dark matter.

A scientist works inside one of the underground rooms of the Compact Muon Solenoid, another of LHC's general-purpose detectors. The CMS experiment is one of the largest international scientific collaborations in history, involving 4,300 particle physicists, engineers, technicians, students and support staff from 182 institutes in 42 countries.

Maintenance work continues inside the CMS. The CMS detector is built around a huge solenoid magnet. This takes the form of a cylindrical coil of superconducting cable that generates a field of 4 tesla, about 100,000 times the strength of Earth's magnetic field.

A unusual feature of the CMS detector is that instead of being built in place like the LHC's other detectors, it was constructed in 15 sections at ground level before being lowered into an underground cavern and assembled. The complete detector is 70 feet long, 50 feet wide and 50 feet high (21 by 15 by 15 meters).

The last bit of maintenance work is perfomed inside the ALICE (A Large Ion Collider Experiment) before it resumes operation in 2015. ALICE is a heavy-ion detector that's designed to study the physics of strongly interacting matter at extreme energy densities.

The ALICE detector sits in a vast cavern almost 200 feet (56 meters) below ground, close to the village of St Genis-Pouilly in France. When ALICE is in operation, the engineers in charge of the LHC switch from using beams of protons to beams of lead ions.

The ALICE collaboration uses a 10,000-ton detector – 85 feet long, 50 feet high and 50 feet wide (26 by 16 by 16 meters) – to study quark-gluon plasma, the "Big Bang soup" that existed when the universe was a trillionth of a second old.

In addition to the experiments at the LHC, scientists at the CERN particle physics center conduct huge numbers of smaller experiments. A bird's-eye view shows one of the experiments in progress.

The Antiproton Decelerator provides low-energy antiprotons, mainly for studies of antimatter. Previously, "antiparticle factories" at CERN and elsewhere consisted of chains of accelerators, each performing one of the steps needed to provide antiparticles for experiments. Now the Antiproton Decelerator performs all the necessary steps, from making the antiprotons to delivering them to experiments. At CERN, scientists have used the antiprotons to create atoms of antihydrogen for a fraction of a second.

The 7,000-ton ATLAS detector is the largest particle detector ever constructed in terms of volume. ATLAS and the Compact Muon Solenoid, or CMS, were instrumental in the successful search for the Higgs boson at the Large Hadron Collider.