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Particle tracks from a proton-proton collision seen by the CMS (compact muon solenoid) 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). A large number of particles (orange lines) were created by the collision. Among them was a Higgs boson. The particle was not seen, but is revealed through its decay products; a pair of Z bosons that each decay into a pair of muons (long red lines). The Higgs boson is thought to give other particles mass. The first sighting of it was announced by scientists at CERN on 4th July 2012. (KEYSTONE/SCIENCE PHOTO LIBRARY/CMS EXPERIMENT, CERN/SCIENCE PHOTO LIBRARY)