International Linear Collider

Standard Model

The International Linear Collider (ILC) is a proposed linear particle accelerator to succeed the Large Hadron Collider (LHC), the world’s largest and highest-energy particle accelerator. The ILC is planned to have a collision energy of 500 GeV initially, with the possibility for a later upgrade to 1,000 GeV (1 TeV).

The host country for the accelerator has not yet been chosen and proposed locations are Japan, Europe (CERN), and the USA (Fermilab). Japan is considered the most likely candidate, as the Japanese government is willing to contribute half of the costs, according to a representative for the European Commission on Future Accelerators.

Construction could begin in 2015 or 2016 and will not be completed before 2026 at an estimated cost of  $10-20 billion. Studies for a competing project called the Compact Linear Collider (CLIC) are also underway, which would operate at higher energies in a shorter-length machine than the ILC. It seems unlikely that both CLIC and ILC machines will be built. There are two basic shapes of accelerators. Linear accelerators (‘linacs’) accelerate elementary particles along a straight path.

Circular accelerators, such as the Tevatron, the Large Electron–Positron Collider (LEP), and the LHC, use circular paths. Circular geometry has significant advantages at energies up to and including tens of GeV: with a circular design, particles can be effectively accelerated over longer distances. Also, only a fraction of the particles brought onto a collision course actually collide. In a linear accelerator, the remaining particles are lost; in a ring accelerator, they keep circulating and are available for future collisions.

The disadvantage of circular accelerators is that particles moving along bent paths will necessarily emit electromagnetic radiation known as synchrotron radiation. Energy loss through synchrotron radiation is related to the mass of the particles in question. That is why it makes sense to build circular accelerators for heavy particles—hadron colliders such as the LHC for protons or, alternatively, for lead nuclei. An electron-positron collider of the same size would never be able to achieve the same collision energies. In fact, energies at the LEP, which used to occupy the tunnel now given over to the LHC, were limited to 209GeV by energy loss via synchrotron radiation.

Even if the effective collision energy at the LHC will be higher than the ILC collision energy (14 TeV for the LHC vs. 1 TeV for the ILC), measurements could be made more accurately at the ILC. Collisions between electrons and positrons are much simpler to analyze than collisions in which the energy is distributed among the constituent quarks, antiquarks and gluons of baryonic particles. As such, one of the roles of the ILC would be making precision measurements of the properties of particles discovered at the LHC. It is widely expected that effects of physics beyond that described in the current Standard Model will be detected by experiments at the proposed ILC. In addition, particles and interactions described by the Standard Model are expected to be discovered and measured.

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