The fundamental constituents of matter

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To find out about the structure of matter, physicists use machines to accelerate particles to high energies. When these particles collide, the collisions are violent enough to disturb exotic particles.
In Europe, LEP, at CERN near Geneva, is the highest-energy electron-positron collider in the world. In the United States, Fermilab in Illinois has the highest-energy proton-antiproton collider.
To understand the results of experiments using these and other machines, physicists have developed the Standard Model. Today they think there are six different quarks. The forces between them are described by a theory, quantum chromodynamics (QCD). Matching these quarks are six leptons (a group including the electron and neutrino). Several different forces operate between quarks and leptons.

Information provided by: http://www.iop.org