An expedition through CERN's underground tunnels

ATLAS detector (2005-11-04) by CERN (Maximilien Brice)CERN

Welcome to CERN! You’ve entered the world headquarters for the study of teeny tiny particles such as protons, neutrons, quarks, neutrinos and the Higgs boson.

You’re 100 meters underground, straddling the border between Switzerland and France. This tunnel is like a 27 kilometer racetrack, and home to the Large Hadron Collider (LHC), where all the particular action happens.

This tunnel lies deep underground to protect it from cosmic rays that might interfere with the research taking place. The tunnel and the LHC it houses form a big circle. That's because particles can pick up more speed when they’re going in a circle versus a straight line. The faster the particles go, the harder they’ll collide with each other.

The big blue pipe is the Large Hadron Collider (LHC) itself. Inside, it accelerates the speed of particles that are smaller than the nuclei of atoms to almost the speed of light. Two streams of particles race around, moving in opposite directions so that they collide. The collisions release fleeting particles that help us understand how the universe started and what it’s made of.

You're looking at CERN’s Compact Muon Solenoid (CMS). But what is a muon? A muon is one type of subatomic particle, far too small and short-lived to be seen. So the CMS helps scientists see the muons’ effects. (If something causes an effect, scientifically, it must exist.) The effects provide data scientists use to figure out what muons are like. CMS is just one of the detectors in use at the Large Hadron Collider.

The red object is one end of the CMS. If you could open it, you’d find a large, magnetic coil of wire. This coil generates a field of 4 tesla, about 100,000 times the magnetic field of the Earth.

CMS may be underground, but it’s also huge. Three of its levels are filled with electronics. While thousands of particles collide every second, computers decide what data to keep and what to discard.

Atlas is the name of an experiment, and also the name of a large device called a detector. Like CMS, Atlas records what happens after particles collide and generates a huge amount of data. But CMS and Atlas work differently. Scientists perform different experiments in search of the same results to confirm the results are valid. When both Atlas and CMS found the Higgs boson, scientists were confident that this particle really does exist.

Inside Atlas, there are magnets, calorimeters, and sensing devices that record what happens after particles collide. To hold all those complex tools, Atlas is as big as a five-story building.

ALICE stands for "A Large Ion Collider Experiment." Many of the experiments at CERN (like Atlas and CMS) study collisions between protons.

The Alice detector tests the properties of particles created by the Hadron Collider. Alice actually includes 18 different detectors that provide information about particles’ momentum, charge, mass, and rate of decay among other things.

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