Scientists believe they have captured the elusive "God particle".
The Higgs boson is regarded as the key to understanding the universe. Physicists say its job is to give the particles that make up atoms their mass.
Without this mass, these particles would zip though the cosmos at the speed of light, unable to bind together to form the atoms that make up everything in the universe, from planets to people.
If the particle was shown not to exist, it would have meant tearing up the Standard Model and going back to the drawing board.
The historic announcement came in a progress report from the Large Hadron Collider and was unveiled at a packed seminar at the Geneva headquarters of Cern, the European Organisation for Nuclear Research.
Professor John Womersley, chief executive of the Science and technology Facilities Council, told reporters at a briefing in London: "They have discovered a particle consistent with the Higgs boson.Discovery is the important word. That is confirmed.
"It's a momentous day for science."