A muon collider is a proposed particle accelerator facility in its conceptual design stage that collides muon beams in order to observe the results. Muons are a type of lepton that occurs only in high-energy collisions caused by cosmic rays or induced in particle accelerators.
Previous lepton colliders have all used electrons, or their anti-particles, positrons. They offer an advantage over hadron colliders, such as the CERN-based Large Hadron Collider, in that lepton collisions are relatively "clean." Leptons are considered elementary particles, while hadrons, such as protons, are composite particles.
While being an elementary particle with low mass, like other leptons, a muon has a rest mass that is higher by a factor of approximately 200 than that of electrons. Thus, synchrotron radiation emitted from a muon is a factor of roughly 109 less than from an electron. The reduced radiation loss enables the construction of circular colliders with much higher design energies than equivalent electron / positron colliders. This permits high energies to be achieved while maintaining a clean collision environment. It has been shown that a muon collider could achieve energies in the teraelectronvolt range.
Talks were proceeding in 2009. The muon accelerator programme was created in 2010, so that the practical considerations for muon collision experimentation might be realized. At Fermilab, a muon collider is the proposed culmination of Project X.