Six quarks and six leptons

Charpak's principle has been used in the DELPHI detector at CERN. The barrelshaped detector is 10 m long and 10 m in diameter. The tracks of the many charged particles created when an electron collides with its antiparticle, the positron, appear on the computer reconstructed picture. By studying such particle collisions, research groups at CERN and SLAC, USA have shown that the fundamental constituents of matter are six types of quark and six types of lepton, one of which is the electron.