Large Hadron Collider

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What is the LHC?

The LHC is exactly what its name suggests - a large collider of hadrons. Strictly, LHC refers to the collider; a machine that deserves to be labelled ‘large’, it not only weighs more than 38,000 tonnes, but runs for 27km (16.5m) in a circular tunnel 100 metres beneath the Swiss/French border at Geneva.

However, the collider is only one of three essential parts of the LHC project. The other two are:

• the detectors, which sit in 4 huge chambers at points around the LHC tunnel and
• the GRID, which is a global network of computers and software essential to processing the data recorded by LHC’s detectors.

The LHC’s 27km loop in a sense encircles the globe, because the LHC project is supported by an enormous international community of scientists and engineers. Working in multinational teams, at CERN and around the world, they are building and testing LHC equipment and software, participating in experiments and analysing data. The UK has a major role in leading the project and has scientists and engineers working on all the main experiments.

What will the LHC do?

The LHC will allow scientists to probe deeper into the heart of matter and further back in time than has been possible using previous colliders.

Researchers think that the Universe originated in the Big Bang (an unimaginably violent explosion) and since then the Universe has been cooling down and becoming less energetic. Very early in the cooling process the matter and forces that make up our world ‘condensed’ out of this ball of energy.

The LHC will produce tiny patches of very high energy by colliding together atomic particles that are travelling at very high speed. The more energy produced in the collisions the further back we can look towards the very high energies that existed early in the evolution of the Universe. Collisions in the LHC will have up to 7x the energy of those produced in previous machines; recreating energies and conditions that existed billionths of a second after the start of the Big Bang.

The results from the LHC are not completely predictable as the experiments are testing ideas that are at the frontiers of our knowledge and understanding. Researchers expect to confirm predictions made on the basis of what we know from previous experiments and theories. However, part of the excitement of the LHC project is that it may uncover new facts about matter and the origins of the Universe.

One of the most interesting theories the LHC will test was put forward by the UK physicist Professor Peter Higgs and others. The different types of fundamental particle that make up matter have very different masses, while the particles that make up light (photons) have no mass at all. Peter’s theory is one explanation of why this is so and the LHC will allow us to test the theory. More of the Big Questions about the universe that the LHC may help us answer can be found here.

How does the LHC work?

The LHC accelerates two beams of atomic particles in opposite directions around the 27km collider. When the particle beams reach their maximum speed the LHC allows them to ‘collide’ at 4 points on their circular journey.

Thousands of new particles are produced when particles collide and detectors, placed around the collision points, allow scientists to identify these new particles by tracking their behaviour.

The detectors are able to follow the millions of collisions and new particles produced every second and identify the distinctive behaviour of interesting new particles from among the many thousands that are of little interest.

As the energy produced in the collisions increases researchers are able to peer deeper into the fundamental structure of the Universe and further back in its history. In these extreme conditions unknown atomic particles may appear.

Who is involved?

The LHC project includes 111 nations in designing, building and testing equipment and software, participating in experiments and analysing data. It is a remarkably harmonious international collaboration in which the UK has a leading role. British scientists and engineers have prominent roles in construction, management and experimental teams and the UK makes a significant contribution to the LHC budget.

CERN has many opportunities for students, postdoctoral researchers, scientists and technical experts in a range of disciplines (links to Working @ CERN)

UK research groups involved in the LHC project.

Over the 13 year construction period (1994 to 2006 inclusive) the total UK contribution for the detectors, GriddPP (materials and staff effort) and collider was £511M. This includes the UK’s annual CERN subscription over this period. This is less than the price of one pint of beer per UK adult per year.

The total cost to the UK of participating in the LHC project will be £108M per year, including £82M per year as its national subscription to CERN’s on-going annual budget of approximately £455M. The subscription of member countries to the CERN budget is linked to their GDP. Non-member countries are also involved in, and contribute to, experiments.

The cost of the LHC project (machine and personnel) is £2.1bn, or £3.5bn if the infrastructure costs, incurred during the construction phase, and the costs of computing, GRID, early running etc are included. The cost of the LHC is mainly paid for by the 20 members of CERN, with significant contributions from the 6 observer nations.

Who benefits?

There are two types of benefit that the LHC project produces for the UK. The less easily measured benefits are:

• new understanding of the physical world,
• training of world class scientists and engineers,
• maintenance of a vibrant, world class UK research base and,
• a leading role in a major international project.

More easily appreciated are the knowledge, expertise and technology that is spun off from the LHC and can be directly applied to development of new medical, industrial and consumer technologies.

The science of the LHC is far removed from everyday life, but the fact that the science is so extreme constantly pushes the boundaries of existing technical and engineering solutions. Simply building the LHC has generated new technology.

The LHC is not primarily about building a better world. Rather, it allows us to test theories and ideas about how the Universe works, its origins and evolution. The questions asked, and answers found, are so fundamental that the information from LHC experiments will only be applied many years in the future, if at all. However, this is an experiment and one of the surprises from the experiment may be new science that can be applied almost immediately.

Where is the LHC?

The LHC is physically located in a circular 27km (16.5m) long tunnel under the Swiss/French border outside Geneva, but as an international project the LHC crosses continents and many international borders.

In the UK, engineers and scientists at 20 research sites are involved in designing and building equipment and analysing data. UK researchers are involved with all four of the main detectors and the GRID. British staff based at CERN have leading roles in managing and running the collider and detectors.

Most, if not all, research teams are contributing to GridPP. UK LHC centres:

• Brunel University, (CMS)
• Imperial College - University of London, (CMS, LHCb)
• Lancaster University, (ATLAS)
• Oxford University, (ATLAS, LHCb)
• Queen Mary - University of London, (ATLAS)
• Royal Holloway – University of London, (ATLAS)
• STFC Rutherford Appleton Laboratory, (ATLAS, CMS, LHCb)
• University College London, (ATLAS)
• University of Birmingham, (ATLAS, ALICE)
• University of Bristol, (CMS, LHCb)
• University of Cambridge, (ATLAS, LHCb)
• University of Durham, (theory)
• University of Edinburgh, (LHCb, GridPP)
• University of Glasgow, (ATLAS, LHCb theory)
• University of Liverpool, (ATLAS, LHCb)
• University of Manchester, (ATLAS)
• University of Sheffield, (ATLAS)
• University of Sussex, (theory)
• University of Swansea,
• University of Warwick,
• University of the West of England

What next?

The LHC is still new, but its successor - the International Linear Collider (ILC) – is already being discussed. So why build two high energy colliders that operate on the same principles?

The LHC is a ‘discovery’ machine, a general purpose tool that will open up new areas of physics and demonstrate the existence, or not, of predicted new laws and particles. The ILC is a precision instrument that will allow scientists to explore in detail the discoveries made by the LHC.

The ILC is still at the planning stage, no location for the machine has been agreed and much feasibility testing has to be conducted before the construction phase.

For Students

Exploring the outer limits of knowledge

The LHC is the most exciting science adventure of this decade; a huge international project exploring the boundaries of our knowledge and theories about the world we live in. The LHC experiments will help us understand the origins and evolution of our universe and possibly reshape how we think about the physical world. Screen shot of particle detectives home page

See a young physicist describing how the study of particle physics has affected our lives and our understanding of the universe we live in and hear how the LHC may be our window into a weird world of missing matter and quantum physics.

teachers.tv/video/23645 the fundamental building blocks of nature,

teachers.tv/video/23903 the fundamental forces of nature,

teachers.tv/video/23904 the quantum world and the hunt for the Higgs boson.

Drive our simulator at [www.particledetectives.net www.particledetectives.net] and learn how LHC scientists will conduct their experiments. This website includes a collection of resources for 14-16 and 16+ year old students on 'how science works' and particle physics. Your own discoveries or listen to the video clips of students questionning scientists about the LHC project and download Powerpoint presentations on LHC science.

There are simulations and pages of information on particle physics at the Lancaster Particle Physics pages. These are suitable for AS/A2 16+ students. There is a section dedicated to the LHC.

A simple game that illustrates how scientists search for new particles can be found on the Science Museum's website.

UK scientists have major roles in this project, which involves thousands of scientists and engineers from around the world working in harmony, to build and run the biggest experiment in the history of science. The project will continue for at least 15 years, so anyone considering science as a GCSE option now could be working on the LHC ... and contributing to new discoveries … in the future.

The science of the LHC is directly relevant to areas of the A-level (and equivalent) curriculum, but the project is also an example of how science works and there are many role models and career stories among the diverse community of scientists, engineers and administration staff working on the LHC.

A lot of resources on the LHC and particle physics are available and more will be produced over the life of the project. Visit the resources pages on the STFC website to download, or order, a stunning A1 poster of the ATLAS detector and an A5 fold out booklet that describes some of the big questions that researchers expect the LHC to answer. You can also download a poster describing the CMS detector (jpg 69kb) and a booklet describing the evolution of the universe (pdf 9.1mb) from the CMS area of CERN website. The ATLAS experiment has two posters available to download (or order) from the ATLAS store. Booklets, DVDs and other materials are also available.

== FAQs ==

I have heard that the LHC will recreate the Big Bang, does that mean it might create another Universe and if so what will happen to our Universe?

People sometimes refer to recreating the Big Bang, but this is misleading. What they actually mean is:

• recreating the conditions and energies that existed shortly after the start of the Big Bang, not the moment at which the Big Bang started,
• recreating conditions on a microscale, not on the same scale as the original Big Bang and,
• recreating energies that are continually being produced naturally (by high energy cosmic rays hitting the earth’s atmosphere) but at will and inside sophisticated detectors that track what is happening.

No Big Bang – so no possibility of creating a new Universe.

How much does the LHC cost and who pays?

The direct total LHC project cost is £2.6bn, made up of:

• the collider (£2.1bn),
• the detectors (£575m).

The total cost is shared mainly by CERN's 20 Member States, with significant contributions from the six observer nations.

UK’s direct contribution to the LHC is £34m per year, or less than the cost of a pint of beer per adult in the UK per year:

The UK pays £70m per year as our annual subscription to CERN.

The LHC project involves 111 nations in designing, building and testing equipment and software, participating in experiments and analysing data. The degree of involvement varies between countries, with some able to contribute more financial and human resource than others.

CERN stands for 'Conseil Européen pour la Recherche Nucléaire' (or European Council for Nuclear Research); does that mean that CERN is studying nuclear power and nuclear weapons?

At the time that CERN was established (1952 – 1954) physics research was exploring the inside of the atom, hence the word ‘nuclear’ in its title. CERN has never been involved in research on nuclear power or nuclear weapons, but has done much to increase our understanding of the fundamental structure of the atom.

The title CERN is actually an historical remnant. It comes from the name of the council that was founded to establish a European organisation for world-class physics research. The Council was dissolved once the new organisation (the European Organization for Nuclear Research) was formed, but the name CERN remained.

Why is the LHC underground? Is it because it is doing secret experiments that scientists want to hide away?

The LHC has been built in a tunnel originally constructed for a previous collider (LEP – the Large Electron Positron collider). This was the most economic solution to building both LEP and the LHC. It was cheaper to build an underground tunnel than acquire the equivalent land above ground. Putting the machine underground also greatly reduces the environmental impact of the LHC and associated activities.

The rock surrounding the LHC is a natural shield that reduces the amount of natural radiation that reaches the LHC and this reduces interference with the detectors. Vice versa, radiation produced when the LHC is running is safely shielded by 50 – 100 metres of rock.

Can the work at CERN be used to build more deadly weapons?

Unlikely for two main reasons. Firstly, CERN and the scientists and engineers working there have no interest in weapons research. They are trying to understand how the world works, not how to destroy it.

Secondly, the high energy particle beams produced at the LHC require a huge machine (27km long, weighing more than 38,000 tonnes – half the weight of an aircraft carrier), consuming 120MW of power and needing 91 tonnes of supercold liquid helium). The beams themselves have a lot of energy (the equivalent of a Eurostar train travelling at top speed) but they can only be maintained in a vacuum, if released into the atmosphere they would immediately interact with atoms in the air and dissipate their energy in a very short distance.

Are the high energies produced by the LHC dangerous and what happens if something goes wrong?

The LHC does produce very high energies, but these energy levels are restricted to tiny volumes inside the detectors. Many high energy particles, from collisions, are produced every second, but the detectors are designed to track and stop all particles (except neutrinos) as capturing all the energy from collisions is essential to identifying what particles have been produced. Very little of the energy from collisions is able to escape from the detectors.

The main danger from these energy levels is to the LHC machine itself. The beam of particles has the energy of a Eurostar train travelling at full speed and should something happen to destabilise the particle beam there is a real danger that all of that energy will be deflected into the wall of the beam pipe and the magnets of the LHC, causing a great deal of damage. The LHC has several automatic safety systems in place that monitor all the critical parts of the LHC. Should anything unexpected happen (power or magnet failure for example) the beam is automatically ‘dumped’ by being squirted into a blind tunnel where its energy is safely dissipated. This all happens in milliseconds – the beam, which is travelling at 11,000 circuits of the LHC per second, will complete less than 3 circuits before the dump is complete.