The Atlas Experiment

By: Ray
Carroll

While surfing the WWW one day I came across the website for the Atlas Experiment (http://atlasexperiment.org). The project, which is based at the CERN laboratory in Geneva, Switzerland, is centred around a type of particle collider called a Large Hadron Collider (LHC). It is so large in fact that part of it is in Switzerland and part of it is in France. The large hadron collider is essentially a 16-mile long tunnel forming a ring with a diameter of nearly 9km. Atlas is the largest collaborative experiment ever undertaken in the physical sciences and involves over 2,000 scientists and 150 laboratories and universities in 34 countries.

That's nice but what has it got to do with telecommunications or computers? Well in all honesty not too much, but the principles of physics underlie everything we do (especially in the science and technical fields) from driving your car to washing the dishes. Also, since CERN was the "birthplace" of the World Wide Web, I thought it might be interesting to see what else they have been up to.

Before I explain what this enormous piece of equipment does I should fill you in with some background physics. Most people reading this will at least have heard of the Atom. Atoms are tiny particles that constitute all matter in the universe, so as far as you or I are concerned everything we see (and cannot see) is made up of atoms. Atoms are so tiny that a million of them in a line would only measure around 1mm.

An atom itself consists of many smaller particles. Firstly, the atom has a nucleus or core that is orbited by smaller particles called Electrons. If you were to draw this it would resemble the sun surrounded by a number of much smaller planets. Within the nucleus there are further particles of two types. These are called Protons and Neutrons. The protons within the nucleus are all positively charged (+) and neutrons have no charge i.e. they are neutral. Each electron orbiting the nucleus of the atom has a negative (-) charge. In nature opposite charges attract, so a negative will attract a positive and vice versa. It is for this reason that the number of protons in the nucleus is always equal to the number of electrons orbiting the nucleus. For each negatively charged electron orbiting the nucleus there must be a positively charged proton in the nucleus to hold it in orbit. There is usually the same number of neutrons as protons in the nucleus but this is not always necessarily true.

For a long time it was thought that all matter consisted only of protons, neutrons and electrons and that these were the most fundamental particles, i.e. they were the smallest particle. However, starting in the 1940's scientists began to discover many new particles through particle collision experiments.

In 1968 scientists verified the existence of Quarks, which are particles even small than protons and neutrons. In fact protons and neutrons are each made up of 3 quarks, which are held together by other particles called gluons.

How the experiment works: The experiment itself could be thought of as extreme atomic chicken (and no it doesn't involve a 40ft chicken with a skateboard). Particles, moving in opposite directions, are accelerated to tremendous speeds and forced to collide with each other.

However, the result of this collision is not as you might expect. When two particles moving at great speed collide they often produce completely new particles, which may have more mass than the original particles. Imagine two 1 tonne cars colliding head on but instead of 2 tonnes of car parts in the debris, this collision produced a caravan, two tractors and a bicycle. The faster the particles are moving the more energy they have, so when they collide this energy is converted into mass. Hence the resulting particles will have a greater mass. The Atlas collider accelerates each of two counter-rotating beams of protons to 7 TeV (trillion electron volts) per proton. The highest energy accelerator before Atlas accelerated protons to only 1 TeV. When I say "only" keep in mind that 1 TeV roughly equates to 1 trillion batteries. This means the particles will be moving at practically (99.999%) the speed of light, which is around 670 million miles per hour.

The most important part of this gargantuan piece of equipment is called the collision chamber or detector. This is where the actual collision between particles occur and is itself about the size of a 5 story building. The detector is divided into a number of layers each responsible for detecting different aspects of a collision. In the Atlas detector there will be about a billion collision events per second, a data rate equivalent to twenty simultaneous telephone conversations by every person on the earth, so a very powerful computer is used to record and analyse the data.

So what's the point of all this? Well much of what goes on in the universe is still unexplainable by current physics knowledge. The long-term goal of physics is to develop a Grand Unified Theory combining many of the important physics theories and then ultimately produce the Theory of Everything. Experimental physics is a slow, incremental process but it is hoped that the Atlas project will lead scientists to the next step in the realisation of physics ultimate goals.