The Large Hadron Collider (LHC) is a particle accelerator which will probe deeper into matter than ever before. Due to switch on in 2007, it will ultimately collide beams of protons at an energy of 14 TeV . Beams of lead nuclei will be also accelerated, smashing together with a collision energy of 1150 TeV. A TeV is a unit of energy used in particle physics. 1 TeV is about the energy of motion of a flying mosquito. What makes the LHC so extraordinary is that it squeezes energy into a space about a million million times smaller than a mosquito. The LHC is the next step in a voyage of discovery which began a century ago. Back then, scientists had just discovered all kinds of mysterious rays, X-rays, cathode rays, alpha and beta rays. Where did they come from? Were they all made of the same thing, and if so what? These questions have now been answered, giving us a much greater understanding of the Universe. Along the way, the answers have changed our daily lives, giving us televisions, transistors, medical imaging devices and computers. On the threshold of the 21st century, we face new questions which the LHC is designed to address. Who can tell what new developments the answers may bring? Because our current understanding of the Universe is incomplete! We have seen that the theory we use, the Standard Model, leaves many unsolved questions. Among them, the reason why elementary particles have mass, and why are their masses different is the most perplexing one. It is remarkable that such a familiar concept is so poorly understood. The answer may lie within the Standard Model, in an idea called the Higgs mechanism. According to this, the whole of space is filled with a ‘Higgs field’, and by interacting with this field, particles acquire their masses. Particles which interact strongly with the Higgs field are heavy, whilst those which interact weakly are light. The Higgs field has at least one new particle associated with it, the Higgs boson. If such particle exists, the LHC will be able to make it detectable. And what about the four forces? When the Universe was young and much hotter than today, perhaps these forces all behaved as one. Particle physicists hope to find a single theoretical framework to prove this, and have already had some success. Two forces, the electromagnetic force and the weak force were ‘unified’ into a single theory in the 1970s. This theory was experimentally verified in a Nobel prize winning experiment at CERN a few years later. The weakest and the strongest forces, however, gravity and the strong force, remain apart. A very popular idea suggested by the unification of the forces is called supersymmetry, or SUSY for short. SUSY predicts that for each known particle there is a ’supersymmetric’ partner. If SUSY is right, then supersymmetric particles should be found at the LHC. The LHC will also help us solve the riddle of antimatter. It was once thought that antimatter was a perfect ‘reflection’ of matter - that if you replaced matter with antimatter and looked at the result in a mirror, you would not be able to tell the difference. We now know that the reflection is imperfect, and this could have led to the matter-antimatter imbalance. The LHC will be a very good ‘antimatter-mirror’, allowing us to put the Standard Model through one of its most gruelling tests yet. These are just a few of the questions the LHC should answer, but history has shown that the greatest advances in science are often unexpected. Although we have a good idea of what we hope to find at the LHC, nature may well have surprises in store. One thing is certain, the LHC will change our view of the Universe. By using superconductivity. To keep the LHC’s beams on track needs stronger magnetic fields than have ever been used before in a CERN accelerator. Superconductivity makes such fields possible, but a superconducting installation as large as the LHC has never before been built. Intensive R&D with European industry has shown that it can be done. At the end of 1994, an important milestone was reached with the first operation of an entire prototype section of the accelerator. Superconductivity is the ability of certain materials to conduct electricity without resistance or energy loss, usually at very low temperatures. The LHC will operate at about 300 degrees below room temperature, even colder than outer space. With its 27 km circumference, the accelerator will be the largest superconducting installation in the world. Because the LHC will accelerate two beams moving in opposite directions, it is really two accelerators in one. To keep the machine as compact and economical as possible, the magnets for both will be built into a single 2-in-1 housing. The LHC will be built in the same tunnel as CERN’s Large Electron Positron collider, LEP, and so will cost much less than a similar machine on a green field site. Proton beams will be prepared by CERN’s existing accelerator chain before being injected into the LHC. The Laboratory’s practice of linking accelerators in this way has made CERN the most versatile particle beam factory in the world. Five experiments, with huge detectors, will study what happens when the LHC’s beams collide. They will handle as much information as the entire European telecommunications network does today! As well as having the highest energy of any accelerator in the world, the LHC will also have the most intense beams. Collisions will happen so fast (800 million times a second) that particles from one collision will still be travelling through the detector when the next collision happens. Understanding what happens in these collisions is the key to the LHC’s success. The experiments are: ATLAS CMS ALICE LHCb TOTEM http://public.web.cern.ch/Public/Content/Chapters/Spotlight/SpotlightCCC-en.html