**This page was archived on 1 December 2008
as the content is out of date**
The LHC is now being constructed by CERN (The European Laboratory for
Particle Physics) in the tunnel which currently houses the Large Electron
Positron (LEP) collider on the outskirts of Geneva. The 27 km circular tunnel
lies on average 100 m below ground, between Lake Geneva and the Jura mountains.
The LEP collider will be removed after October 2000 when it will have completed
its mission of improving our understanding of the Standard Model, which is, so
far, our best description of sub-atomic Nature. LEP has given us a preview of
exciting discoveries that may be made at higher energies and the LHC has been
designed to seek answers to profound questions and investigate new physics at
those higher energies.
COUNTRIES COLLABORATING IN THE LHC PROJECT
The LHC is an international endeavour with the UK being among over forty
countries participating in the project. Countries collaborating in the LHC
project are Armenia, Australia, Austria, Azerbaijan Republic, Belarus, Belgium,
Brazil, Bulgaria, Canada, China, Croatia, Cyprus, Czech Republic, Denmark,
Estonia, Finland, France, Georgia, Germany, Greece, Hungary, India, Israel,
Italy, Japan, Korea, Morocco, Netherlands, Norway, Pakistan, Poland, Portugal,
Romania, Russia, Slovak Republic, Slovenia, Spain, Sweden, Switzerland, Turkey,
Ukraine, United Kingdom, United States, Uzbekistan.
AIMS OF THE LHC PROJECT
Although the success of the Standard Model has been remarkable, it fails to
address some important questions. The goal for the LHC is to answer
experimentally the outstanding questions, such as:
What is mass?
In the Standard Model, all particles acquire their masses by interacting
with another particle, the Higgs Boson, named after Peter Higgs of Edinburgh
University. It is the strength of this interaction that gives rise to what we
know familiarly as mass. Experiments have yet to show whether this theory is
correct, but we do know that there must be a mechanism to give particles their
masses, and that the associated new physics must emerge at energies accessible
at the LHC.
Is there supersymmetry?
Attempts to develop a "grand unified theory", in which the electroweak and
the strong interactions are brought together within a single framework, suggest
that a deep symmetry, known as "supersymmetry", will become manifest at the
energies of the LHC. Supersymmetry links the matter particles (the quarks and
leptons) with the force particles (the gauge bosons) and predicts that there
are additional "superparticles" necessary to complete the symmetry. The
superparticles should have masses within the range of the LHC, around ten times
greater than the heaviest particles studied so far.
What is Dark Matter?
The discovery of supersymmetric particles could have important implications
for cosmology. Measurements in astronomy suggest that more than 90% of the
universe is in the form of "Dark Matter", so far revealed only through its
gravitational attraction. The lightest supersymmetric particles could be
stable, in which case large numbers of them, created in the early universe,
could now have clustered into structures of Dark Matter on the scale of
galaxies.
Where has all the antimatter gone?
In the very early moments after the Big Bang (the start of the universe),
the universe should have contained equal amounts of matter and antimatter. When
matter and antimatter particles meet, they annihilate each other. Yet, the
universe we see around us is made up almost entirely of matter. We expect
experiments at the LHC to cast light on the puzzle of how the matter we see in
our universe survived this primordial mutual annihilation.
Our present understanding of the asymmetry between matter and antimatter is
inextricably tied up with the existence of three generations of quarks and
leptons, and the studies at the LHC will provide an important new window on
this effect.
Why are there six quarks?
Although we know that there are three "generations" of quarks and leptons,
we do not know why there are three, or why the one that forms the world about
us is not enough. The answer to this question is probably linked to the answers
to the other questions, and in particular to the ideas of supersymmetry and the
resolution of the matter - antimatter problem. Collisions at the LHC will
readily produce particles containing even the heaviest quarks and will allow us
to study them and their interactions in unprecedented detail.
The energy region around 1 TeV promises to reveal new physics that will
address these questions. Exploring this energy region is the goal for the LHC.
The easiest way to reach 1 TeV is by colliding together proton beams, as
protons are relatively easy to produce and to accelerate. However, protons are
complex objects, containing quarks and gluons (carriers of the strong force)
amongst which the energy is shared. So in order to reach energies in the region
of 1 TeV, the LHC's primary role will be to collide proton beams with higher
energies, around 7 TeV. The machine will consist of a ring of superconducting
magnets, 27-km in circumference. The twin-aperture magnets constrain the orbits
of two beams of protons, circulating in opposite directions, allowing each of
them to be accelerated to 7 TeV and stored at that energy for periods of up to
a day. The two beams cross at four points around the ring , where they can be
brought into head-on collision at a centre of mass energy of 14 TeV. Detectors
are placed at each of the four intersections.
UK PARTICIPATION IN THE LHC
UK scientists are leaders in several key scientific and technological areas
in the LHC project. Funding has been approved for UK scientists to take part in
the four LHC experiments and consequently, over recent years, the UK particle
physics community has led the construction of vital components
for ATLAS (A Toroidal LHC Apparatus), CMS (Compact Muon Solenoid), ALICE (A
Large Ion Collider Experiment) and LHC-B (LHC - Beauty).
The UK groups that will take part in the experiments are from Birmingham,
Bristol, Brunel, Cambridge, Edinburgh, Glasgow, Lancaster, Liverpool,
Manchester, Oxford and Sheffield Universities; Imperial College of Science
Technology and Medicine; Queen Mary and Westfield College; Royal Holloway and
Bedford New College; University College London and Rutherford Appleton
Laboratory..
ATLAS and CMS have several functions and so they are called general-purpose
detectors. Studies at both of these detectors will include the search for Higgs
bosons and supersymmetric particles. Although their physics goals are similar,
the design philosophies of the two detectors are different and so they should
provide corroboration of each other's results. UK groups are taking leading
roles in the design and construction of crucial elements of these detectors and
will eventually hold prominent positions in the commissioning and operation of
the experiments.
In addition to colliding protons, the LHC will smash together ions of lead
at speeds which will produce energy densities as high as in the first fraction
of a second of the start of the Universe. The lead ions will be collided at the
ALICE detector where the plasma produced will be studied. The vital trigger for
this experiment was designed and developed by the UK.
The LHC-B experiment is designed to study the violation of symmetries and
other rare phenomena in B-meson decays. This should lead to an understanding of
why there is apparently so little antimatter in the Universe, when matter and
antimatter should have been produced in equal amounts at the Big Bang. The
contribution of UK groups to LHC-B includes designing and developing the
particle identification detectors and high level trigger.
STFC provides research grants and studentships to UK institutes working on
the LHC project, and funds the UK membership of CERN.
COSTS
The cost of building the LHC will be £2.1 billion over 13 years, of
which, the UK's contribution will be around 16%.
TIMESCALE
The LHC is due to be completed in 2008.
PICTURES
FURTHER INFORMATION
Further information on the LHC project can be found on the CERN Website (link opens in a new window).
Page last updated: 01 December 2008
by Charlotte Jamieson
