# International Linear Collider: Another particle accelerator

Updated on October 15, 2015

## What is a linear particle accelerator?

The type of particle accelerator that accelerates the particle along a straight beamline using oscillating electric potentials, also called as a linac. The beamline refers to the path an accelerated particle takes.

## How is a linear particle accelerator different from a circular accelerator?

In a circular accelerator, the particles accelerate in a circular path and this is maintained by electromagnets. The advantages over the linacs include:

• Circular accelerators allow for continuous acceleration.
• A linac would need to be longer to have an equivalent power of a circular accelerator.

## Circular accelerators have a main disadvantage

But circular accelerators cause the particles being accelerated to emit synchrotron radiation, which is the type of electromagnetic radiation emitted by a particle that is being accelerating radially. As this emission of radiation depends upon energy, mass and the type of particle being accelerated, high energy electron accelerators are preferred to be linacs.

## What is a Higgs boson?

The Higgs boson is an elementary particle found in the Standard Model, which is a theory from particle physics. The Standard Model is the theory, which is concerned with the electromagnetic, strong and weak interactions that occur at the nuclear level that also classifies the sub-atomic particles. These particles can be categorized as elementary particles, having no other constituent particles and the composite particles such as protons or neutrons made up of quarks. Here quarks could be considered as elementary particles and protons or neutrons are composite particles.

## Higgs boson is the excitation of the Higgs field

Higgs boson is believed to be the quantum excitation of one of the four components of the Higgs field which plays a role in the mass gained by other elementary particles. The question is why, according to symmetry, the fundamental particles are not massless? Quantum excitation refers to an excited state, the energy state that is higher than the ground state which is the lowest energy state. Most particles are excitations of their related fields. According to hypotheses, Higgs field is thought to permeate all over the Universe and currently it is suggested that the field exists.

It would explain why the weak force has a very short range.

## The discovery of the particle consistent with the Higgs boson

The Higgs boson came up as a theory in the 1960s when the Higgs mechanism, also known as the Englert–Brout–Higgs–Guralnik–Hagen–Kibble mechanism, was proposed in 1964. Eventually the Large Hadron Collider (LHC) was constructed with the goal of high-energy tests related to the Standard Model, particle physics and to confirm whether Higgs boson existed or did not exist. After 48 years of search efforts, the Higgs boson was confirmed to exist after the discovery of a particle with behavior consistent to that of the boson by two teams working in isolation from each other – the CMS and the ATLAS experiment teams on 4 July 2012.

From the Standard Model, it should be understood that Higgs boson is without spin (scalar particle), has no electric charge or color charge and decays very quickly into other particles. It has mass within the range of 125 – 127 GeV. The boson is suggested to couple to other particles with strength proportional to the particle’s mass and it is also said to couple with itself.

As more details about the Higgs boson are required, the stage is set for further research. The International Linear Collider is one such tool that would help with this.

## What is the International Linear Collider (ILC)?

It is a planned 500 GeV – 1000 GeV linear particle accelerator which will have a length in the range 30 – 50 km and is going to be located in a tunnel 100 m underground. The ILC will be concerned with the collisions of electrons and positrons travelling at nearly the speed of light.

Its significant purposes are:

• To investigate the unknown mysteries of the sub-atomic particles
• To uncover the factors behind the origin of the universe
• To discover more unknown particles which originate during the collisions between electrons and positrons
• To study the Higgs boson in more detail

## The top candidate sites

The proposed host countries for the ILC include Japan, CERN in Europe and the Fermilab in the United States. Regarding the choice of Japan as the host country, the ILC site evaluation committee of Japan began searching for a suitable site of construction. After the ILC site evaluation committee assessed the Kitakami region and the Sefuri region between the Saga and the Fukuoka prefectures , the ILC is planned to be built at the Kitakami region in the Iwate prefecture, north of Japan if it is selected as the host country.

In the Kitakami region, it would stretch from Esashi, Oshu to Morone, Ichinoseki. The ILC would then cross under the undulating hills of the Kitakami and the collision of the beams would occur near Ohara town under the mountain Hayamayama. The 50-km option would stretch out till the Kesennuma city.

## Linear accelerator

Using the ILC, the collisions between the electrons and positrons will be produced. Two linear particle accelerators are required to accelerate both the particles towards collision point. These linacs would operate at -271 degree Celsius and the particles will reach the energy scale of 250 GeV at the collision point.

## Positrons

The positrons are produced by sending high-energy electron beams (250 GeV) through undulators which is a type of insertion device. An insertion device is a grouping of magnets placed on a straight segment of the particle accelerator generally as a synchrotron light source. These devices are used instead of pipes that would need vacuum to maintain the path of the particles.

As the electron beam passes through the undulator, there is turbulence in their path causing the electrons to emit a stream of photons. The electrons return to the main accelerator after passing the undulator and the photons hit a titanium-alloy target, generating pairs of electrons and positrons. These positrons will be collected before being accelerated to 5 GeV through their respective particle accelerator.

## Electrons

Electrons are produced when high-intensity, two-nanosecond light pulses are fired from a laser at a target to knock out billions of electrons per each pulse. The electrons are then gathered into groups by electric and magnetic fields before launching, initially at 5 GeV, through the linear accelerator.

## Damping rings

Devices called damping rings are used to bring both the electrons and positrons to required densities for the collisions inside the detector. Inside these rings, another type of insertion device called wigglers are used. Wigglers consist of magnets that are arranged in a sequence designed for periodical lateral deflections (also termed as “wiggle”) of the beams of the particles to produce photons. Each group of particles will circle the rings 10,000 times in two-tenths of a second.

## Compression into bunches

The bunches of electrons and positrons from their respective damping rings will be accelerated initially from 5 GeV to 15 GeV before heading for the collision point. They will be compressed using special technology and magnets before colliding.

## Detectors

At nearly the speed of light, the groups of electrons and positrons collide with a total energy of 500 GeV. Two giant particle detectors will then record the collisions, and the particles generated due to the electron-positron annihilations. Information of every particle produced is to be acquired.

## ILC is complementary to the LHC

While the Large Hadron Collider studied interactions of the proton and their constituents at high-energy levels, the ILC will study collisions between electrons and positrons. These two particles are considered as elementary particles and the simple elementary processes that would occur can be studied with more attention at the ILC. The device could discover new details and particles that could be missed by the LHC. LHC will work at the TeV scale while ILC work at the GeV scale.

## The ILC and the Higgs boson

• ILC will allow measurements of the strength with which the Higgs boson interacts with other particles having different masses.
• ILC allows for accuracy in measuring Higg’s self-coupling and the potential. This is for confirming whether the particle will be according to the Standard Model.
• The ILC has to perform measurements that play a role in deciding the fate of the Standard Model, measuring the values of Higgs mass and the mass of the top quark (the heaviest subatomic particle discovered, being about as heavy as a Gold atom).

## The ILC and Dark Matter

ILC can measure mass, parity (a concept that relates to symmetry of the wave function that represents the system of elementary particles) and spin (the amount of angular momentum that is related to a subatomic particle) of particles that may have associations with dark matter if it is possibly found by the LHC at the TeV scale.

## The ILC and Supersymmetry

Supersymmetry suggests that all of the observed elementary particles, which are either fermions or bosons have superpartners. These are hypothetical elementary particles, also called “shadow” particles, and could be associated to particles in the other group i.e., one particle can have a superpartner in the other group. As given on a list of unsolved problems in Physics on Wikipedia, supersymmetry may be related to dark matter, whether dark matter could be comprised of lighter superpartners. Linear colliders are suited for producing such particles and could concentrate on one type of superpartner at one time and measure their properties in a precise manner, and find the relation between Supersymmetry and Dark Matter. Scientists could also learn how Supersymmetry is related to the shaping of the Universe. From all of these it can be understood that the ILC is suited for studying dark matter particles.

## The ILC and Extra Dimensions

The Superstrings theory suggests that there could be more dimensions in the Universe, along with space and time. These extra dimensions are believed to be very tiny, subject to compactification (changes in theory with respect to its space-time dimension i.e., a theory could have its dimensions finite rather than infinite) or hidden away in the Universe without any proof of existence from conducted experiments. If possible, these dimensions could be identified by trying to measure relevant properties of the particles that move in extra dimensions since matter could already be made of such particles from extra dimensions. The LHC should be able to discover extra dimensions if they exist at the Terascale but ILC could aid in further research by being able to reveal about the structure of the extra dimensions and their related particles in depth.

## How the ILC has great consequences for particle physics?

The ILC should be able to discover more about the Higgs boson and this particle could help to understand more about the Universe. But the ILC is not just limited to the particle as it allows for a practical understanding of new theories and their consistency. And as old theories might have new understanding, such tools would be relevant for uncovering them.

This is an exciting prospect for Physics. New discoveries wouldn’t have limits with such useful devices. There are many more unsolved mysteries in the Universe and scientists, particle physicists have lot of work to do with their tools. The Nobel Prize and the related recognition would always encourage scientific minds in their quest for enquiry into the unknown.

## References

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© 2015 Arun Dev

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Arun Dev

2 years ago from United Countries of the World

@AliciaC Thanks for taking your time to read the hub and commenting!

• Linda Crampton

2 years ago from British Columbia, Canada

This is a very exciting time for physics. Interesting discoveries are being made and fascinating theories are appearing! Thank you for sharing the information.

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