Collider

In particle physics one gains knowledge about elementary particles by accelerating particles to very high kinetic energy and letting them impact on other particles. For sufficiently high energy, a reaction happens that transforms the particles into other particles. Detecting these products gives insight into the physics involved.

To do such experiments there are obviously two possible setups:

• Fixed target setup: A beam of particles (the projectiles) is accelerated with a particle accelerator, and as collision partner, one puts a stationary target into the path of the beam.

• Collider: Two beams of particles are accelerated and the beams are directed against each other, so that the particles collide while flying into opposite directions.

The collider setup is harder to construct but has the great advantage, that according to special relativity the energy of an inelastic collision between two particle approaching each other with a given velocity is not just 4 times as high as in the case of one particle resting (as it would be in non-relativistic physics) but can be orders of magnitude higher for relativistic speeds.

High-end colliders are built as ring accelerators -- with the exception of the proposed TESLA facility which is planned as a linear accelerator. -- See particle accelerators for further discussion.