«The Large Hadron Collider (LHC), the world’s largest and most powerful particle accelerator, is the latest addition to CERN’s accelerator complex. It mainly consists of a 27 km ring of superconducting magnets with a number of accelerating structures to boost the energy of the particles along the way.
Inside the accelerator, two beams of particles travel at close to the speed of light with very high energies before colliding with one another. The beams travel in opposite directions in separate beam pipes – two tubes kept at ultrahigh vacuum. They are guided around the accelerator ring by a strong magnetic field, achieved using superconducting electromagnets. These are built from coils of special electric cable that operates in a superconducting state, efficiently conducting electricity without resistance or loss of energy. This requires chilling the magnets to about ‑271°C – a temperature colder than outer space! For this reason, much of the accelerator is connected to a distribution system of liquid helium, which cools the magnets, as well as to other supply services.
Thousands of magnets of different varieties and sizes are used to direct the beams around the accelerator. These include 1232 dipole magnets of 15 m length which are used to bend the beams, and 392 quadrupole magnets, each 5–7 m long, to focus the beams. Just prior to collision, another type of magnet is used to 'squeeze' the particles closer together to increase the chances of collisions. The particles are so tiny that the task of making them collide is akin to firing needles from two positions 10 km apart with such precision that they meet halfway!All the controls for the accelerator, its services and technical infrastructure are housed under one roof at the CERN Control Centre. From here, the beams inside the LHC will be made to collide at four locations around the accelerator ring, corresponding to the positions of the particle detectors.»
© CERN«Why the LHC
A few unanswered questions...
The LHC was built to help scientists to answer key unresolved questions in particle physics. The unprecedented energy it achieves may even reveal some unexpected results that no one has ever thought of!
For the past few decades, physicists have been able to describe with increasing detail the fundamental particles that make up the Universe and the interactions between them. This understanding is encapsulated in the Standard Model of particle physics, but it contains gaps and cannot tell us the whole story. To fill in the missing knowledge requires experimental data, and the next big step to achieving this is with LHC.
Newton's unfinished business...
What is mass?
What is the origin of mass? Why do tiny particles weigh the amount they do? Why do some particles have no mass at all? At present, there are no established answers to these questions. The most likely explanation may be found in the Higgs boson, a key undiscovered particle that is essential for the Standard Model to work. First hypothesised in 1964, it has yet to be observed.
The ATLAS and CMS experiments will be actively searching for signs of this elusive particle.
An invisible problem...
What is 96% of the universe made of?
Everything we see in the Universe, from an ant to a galaxy, is made up of ordinary particles. These are collectively referred to as matter, forming 4% of the Universe. Dark matter and dark energy are believed to make up the remaining proportion, but they are incredibly difficult to detect and study, other than through the gravitational forces they exert. Investigating the nature of dark matter and dark energy is one of the biggest challenges today in the fields of particle physics and cosmology.
The ATLAS and CMS experiments will look for supersymmetric particles to test a likely hypothesis for the make-up of dark matter.
Nature's favouritism...
Why is there no more antimatter?
We live in a world of matter – everything in the Universe, including ourselves, is made of matter. Antimatter is like a twin version of matter, but with opposite electric charge. At the birth of the Universe, equal amounts of matter and antimatter should have been produced in the Big Bang. But when matter and antimatter particles meet, they annihilate each other, transforming into energy. Somehow, a tiny fraction of matter must have survived to form the Universe we live in today, with hardly any antimatter left. Why does Nature appear to have this bias for matter over antimatter?
The LHCb experiment will be looking for differences between matter and antimatter to help answer this question. Previous experiments have already observed a tiny behavioural difference, but what has been seen so far is not nearly enough to account for the apparent matter–antimatter imbalance in the Universe.
Secrets of the Big Bang
What was matter like within the first second of the Universe’s life?
Matter, from which everything in the Universe is made, is believed to have originated from a dense and hot cocktail of fundamental particles. Today, the ordinary matter of the Universe is made of atoms, which contain a nucleus composed of protons and neutrons, which in turn are made quarks bound together by other particles called gluons. The bond is very strong, but in the very early Universe conditions would have been too hot and energetic for the gluons to hold the quarks together. Instead, it seems likely that during the first microseconds after the Big Bang the Universe would have contained a very hot and dense mixture of quarks and gluons called quark–gluon plasma.
The ALICE experiment will use the LHC to recreate conditions similar to those just after the Big Bang, in particular to analyse the properties of the quark-gluon plasma.
Hidden worlds…
Do extra dimensions of space really exist?Einstein showed that the three dimensions of space are related to time. Subsequent theories propose that further hidden dimensions of space may exist; for example, string theory implies that there are additional spatial dimensions yet to be observed. These may become detectable at very high energies, so data from all the detectors will be carefully analysed to look for signs of extra dimensions.»
