# International Linear Collider

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## Introduction

### The state of particle physics

The field of particle physics has taken nations from all over the world into huge collaborations. The biggest project so far, the Large Hadron Collider (LHC) in Cern, Geneva, is a multi billion dollar project, with thousands of scientist collaboration on many projects. A new collider, the International Linear Collider is destined to be built in Japan, it is going to be 31 km and will smash together electrons and protons to produce Higgs bosons. Compared to the LHC, the ILC is a linear collider and not a hadron collider, which will result in very precise measurements etc… In order to understand the purpose of building this giant machine, let us briefly examine the current state of particle physics. As of late 2016 - the state of our understanding of particle physics is, roughly, as follows.

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Particles at an elementary level do not operate under the same kind of physical laws as normal (big) particles do. Instead, they live in a quantum universe where they exist in a duality with a wave-like existance obeying the laws Quantum Field Theories such as Quantum Electrodynamics (describing the electromagnetic force), Quantum Chromodynamics (describing the strong force) and Quantum Flavourdynamics (describing the weak force). Up until 2012, the experimentally detected elementary particles (we have yet not found any compelling evidence of a substructure of these particles) were the matter and antimatter particles called fermions (quarks, leptons and their antiparticles) and the gauge bosons (gluon, photon, Z,W) which are the force carrying particles and mediate interactions between the fermions. In 2012, the Higgs Boson was discovered in the Large Hadron Collider (LHC) in Cern, Geneva, this discovery completed the observation of the last particle in the currently leading framework of particle physics, the Standard Model. The Standard Model has so far produced highly successful predictions in experiments and is though to be self consistent(citation not found: wiki). Although, as the frontiers of physics are comstantly pushed forward, we must ask ourselves:

”Is there any physics beyond the Standard Model?”

One could argue that this question could be asked regarding every concievable physical theory and that it should always be the job of a physicist to ask this question. But there is also a need for a deeper understanding of the physical laws of nature if we want to describe certain phenomena in the world, i.e. there are phenomena which can not be explained by the Standard Model, thus it can not be a complete theory of fundamental physics (popularly called the Theory of Everything).

To answer this very profound question, one must work in a broad manner, combining the efforts of theoretists and experimentalists. The next generation of colliders will require high level of precision, this is where the ILC comes in. The main purpose of the ILC is therefore to tackle a few of these unanswered questions such as:

• 1

• 2

• 3

As described in section blabla, there are different advantages and disadvantages for circular and linear colliders. Ever since the building of LHC, the plan has been that to spot the Higgs boson with LHC (done) and then build another accelerator to study its properties in detail. It was decided in blabla that the machine would be a linear colider which would accelerate leptons instead of hadrons. There has since formed two competing camps, one at Fermilab and the other at Cern. Thus the idea behind Compact Linear Collider (CLiC) was born in Cern, the idea was to accelerate leptons within a shorter distance bblabla . The downside being that this had never been done in practise. The ILC counters this problem by using existing technology, the first site for building it was at Fermilab but due to it’s length of 30km + the US Congress cut the funding which pu the project att rest. After the discovery of Higgs and the great earthquake in Japan 2011 the japanese government coughed up some money to pay half of the project. Since then Japan has been the proposed site for the project.

### Scope and outline of the report

This report will mainly focus of the challenges of building a detector which fulfills the required demands, although, a bried introduction to electron positron collisions will be given in section 2. In section 3, the reader will be familiarised with the challenges of building a detector for the ILC. Finally, the Silicon Detector (SiD) will be introduced in section 4, where it’s components will be discussed in relation to the challenges presented in section 3. For a more comprehensive description of the technical aspects of the detector the reader is refered to ”International Linear Collider - Volume 4: Detectors”(The International Lin...) which is also one of the main resources for this report.

## Electron-positron collisions

In the ILC, electrons and positrons are produced by blabla. They are the accelerated in the two 11km long linear accelerators and finally collided in the detectors. By using electron-positron collisions, instead of hadron collision as in the LHC, fewer particles are produced. In each collision in the LHC, thousands of particles are produced, this can be compared to the few hundred particles which will typically be produced per event in the ILC. This makes the measurements easier to conduct and more precise since the background in each experiment is greatly reduced. The energy of the colliding electrons and positrons will be up to around $$1$$ TeV, which is one order of magnutude lower than in the LHC, although, because of the collisions are much simpler than in the LHC, the results will be more precise.