Particle collision event, ATLAS detector. . This computer graphic shows the particle tracks recorded by the ATLAS detector during a particle collision event with 4 muons. The four muons are the long blue tracks. ATLAS (A Toroidal LHC Apparatus) is a particle detector at the Large Hadron Collider (LHC), the world’s largest and most powerful particle collider which began operating in 2008 at CERN, the European particle physics laboratory. Muons are a type of elementary particle similar to electrons but much heavier. This view looks at the detector and beam line from the side. Image published in April 2014.