Collider

A collider is a type of particle accelerator involving directed beams of particles. Colliders may either be ring accelerators or linear accelerators, and may collide a single beam of particles against a stationary target or two beams head-on.

Colliders are used as a research tool in particle physics by accelerating particles to very high kinetic energy and letting them impact other particles. Analysis of the byproducts of these collisions gives scientists good evidence of the structure of the subatomic world and the laws of nature governing it. These may become apparent only at high energies and for tiny periods of time, and therefore may be hard or impossible to study in other ways.

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 occurs that transforms the particles into other particles. Detecting these products gives insight into the physics involved.

To do such experiments there are two possible setups:

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 particles 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); it can be orders of magnitude higher if the collision velocity is near the speed of light.

In the case of a collider where the collision point is at rest in the laboratory frame (i.e. ${\vec {p}}_{1}=-{\vec {p}}_{2}$ ), the center of mass energy $E_{\mathrm {cm} }$ (the energy available for producing new particles in the collision) is simply $E_{\mathrm {cm} }=E_{1}+E_{2}$ , where $E_{1}$ and $E_{2}$ is the total energy of a particle from each beam. For a fixed target experiment where particle 2 is at rest, $E_{\mathrm {cm} }^{2}=m_{1}^{2}+m_{2}^{2}+2m_{2}E_{1}$ .

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