Collider

This article is about the particle accelerator. For other uses, see Collider (disambiguation).

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.

Explanation

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:

• 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 in opposite directions. This process can be used to make strange and anti-matter.

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, $E_{\mathrm {cm} }^{2}=m_{1}^{2}+m_{2}^{2}+2m_{2}E_{1}$.

History

The first serious proposal for a collider originated with a group at the Midwestern Universities Research Association (MURA). This group proposed building two tangent radial-sector FFAG accelerator rings. Tihiro Ohkawa, one of the authors of the first paper, went on to develop a radial-sector FFAG accelerator design that could accelerate two counterrotating particle beams within a single ring of magnets. The third FFAG prototype built by the MURA group was a 50 MeV electron machine built in 1961 to demonstrate the feasibility of this concept.

Gerard K. O'Neill proposed using a single accelerator to inject particles into a pair of tangent storage rings. As in the original MURA proposal, collisions would occur in the tangent section. The benefit of storage rings is that the storage ring can accumulate a high beam flux from an injection accelerator that achieves a much lower flux.

The first electron-positron colliders were built in late 1950's-early 1960's in Italy, at the Istituto Nazionale di Fisica Nucleare in Frascati near Rome, by the Austrian-Italian physicist Bruno Touschek and in the US, by the Stanford-Princeton team that included William C.Barber, Bernard Gittelman, Gerry O’Neill, and Burton Richter. Around the same time, in the early 1960s, the VEP-1 electron-electron collider was independently developed and built under supervision of Gersh Budker in the Soviet Institute of Nuclear Physics.

In 1966, work began on the Intersecting Storage Rings at CERN, and in 1971, this collider was operational. The ISR was a pair of storage rings that accumulated particles injected by the CERN Proton Synchrotron. This was the first hadron collider, as all of the earlier efforts had worked with electrons or with electrons and positrons.

In 1968 construction began on the accelerator complex for the Tevatron at Fermilab. In 1986 the first proton antiproton collisions were recorded at a center of mass energy of 1.8 TeV, making it the highest energy collider in the world, at the time.

The most high-energetic collider in the world (as of 2016) is the Large Hadron Collider (LHC) at CERN. There are several particle collider projects currently under consideration.

Operating colliders

Sources: Information was taken from the website Particle Data Group and Handbook of accelerator physics and engineering.

Accelerator	Centre, city, country	First operation	accelerated particles	max energy per beam, GeV	Luminosity, 1030 cm−2 s−1	Perimeter (length), km
VEPP-2000	INP, Novosibirsk, Russia	2006	е+e−	1.0	100	0.024
VEPP-4М	INP, Novosibirsk, Russia	1994	е+e−	6	20	0.366
BEPC II	IHEP, Beijing, China	2008	е+е−	3.7	700	0.240
DAFNE	Frascati, Italy	1999	е+е−	0.7	436	0.098
KEKB	KEK, Tsukuba, Japan	1999	е+е−	8.5 (e-), 4 (e+)	21100	3.016
RHIC	BNL, United States	2000	pp, Au-Au, Cu-Cu, d-Au	100/n	10, 0.005, 0.02, 0.07	3.834
LHC	CERN	2008	pp, Pb-Pb, p-Pb	6500 (planned 7000), 2560/n (planned 2760/n)	15000, 0.003, 0.9	26.659

See also

• List of colliders
• Large Electron–Positron Collider
• Large Hadron Collider
• Very Large Hadron Collider
• Relativistic Heavy Ion Collider
• International Linear Collider
• Storage ring
• Tevatron
• International Conference on Photonic, Electronic and Atomic Collisions

External links

• LHC - The Large Hadron Collider on the web
• The Relativistic Heavy Ion Collider (RHIC)