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Particle tracks from a proton-proton collision seen by the ATLAS (a toroidal LHC apparatus) detector at CERN (the European particle physics laboratory) near Geneva, Switzerland. Before the collision the ions had been accelerated by the large hadron collider (LHC). Outer parts of ATLAS are shown in grey, the centre of the detector is at bottom left and the muon chambers are shown as green and blue boxes. Insets of the particle tracks are at right and top left. The collision produced a top quark and top antiquark. These particles are not seen, but are revealed through their decay products. The top quark decays into a bottom quark (purple lines and wedges), an electron (green lines), and a neutrino (not seen), while the top antiquark decays into a bottom antiquark (purple lines and wedges), a muon (red lines), and a neutrino (not seen). (KEYSTONE/SCIENCE PHOTO LIBRARY/ATLAS EXPERIMENT, CERN/SCIENCE PHOTO LIBRARY)