ANTIMATTER DECELERATOR - TEACHER'S SUMMARY

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What has happened?

Researchers at CERN have succeeded in commissioning a new research machine that will study the mirror-world of antimatter in depth. It will allow researchers to trap antiprotons and atoms of antimatter and to compare them with their matter equivalents.

Why is this important?

The curious thing about antimatter is that there isn't more of it around. Scientists believe that the Universe began in a Big Bang at which matter and antimatter were created in equal amounts, yet in today's Universe all the antimatter seems to have disappeared. Why has it done so? And why has it not taken all the matter along with it?

Matter and antimatter are perfect opposites. So perfect, in fact, that when the meet they annihilate leaving behind a flash of pure energy. Nothing else remains. That's why science fiction writers like antimatter so much. To them, antimatter annihilation is the ultimate clean source of energy. It is the perfect conversion of mass (m) into energy (E) according to Einstein's famous prescription E= mc², where c is the speed of light. The problem is, however, that antimatter cannot simply be harvested or mined. It has to be made, and making it requires vastly more energy than annihilating it produces. All the antimatter produced at CERN in a year would provide barely enough energy to power a light bulb for a few seconds.

So antimatter as an energy source is destined to remain within the realms of science fiction, but there remains the important question of why nature seems to prefer matter over antimatter to be answered. In experiment after experiment, matter and antimatter display a perfect symmetry. What one does, the other mirrors. When enough energy is concentrated to produce particles, equal numbers of matter and antimatter particles are produced. And when the antiparticles meet their matter counterparts, they disappear returning to pure energy. Nothing is added. Nothing is lost.

We know that this can't be the end of the story. Either the antimatter from the Big Bang is out there somewhere, though that seems very unlikely, or the matter-antimatter symmetry is not quite perfect. The latter we now know to be true. Some subtle experiments have forced nature's hand, revealing a slight bias in matter's favour. This bias translates to just a single proton surviving out of every billion that could have emerged from the Big Bang. It is from this one in a billion that the Universe is made.

CERN's new research machine, the Antiproton Decelerator (AD), allows scientists to trap antimatter in electromagnetic cages where it can not come into contact with matter. There they can study it at leisure, finding out, for example, whether antihydrogen spectroscopy is the same as that of hydrogen. Now that we know nature favours matter over antimatter, research at the AD will help us to understand why.

What use is antimatter?

Antimatter may be the stuff of science fiction but at laboratories like CERN it is a commonplace tool for research. In hospitals and industry too, antimatter is in everyday use for diagnosis. Positron Emission Tomography, PET, for example relies on antimatter. It works by attaching radioactive atoms that emit positrons - anti-electrons - to biological tracer molecules that find their way to specific areas of the body. When the radioactive atoms decay the positrons they emit immediately annihilate with electrons and the resulting flash of energy appears in the form of two gamma-rays of equal energy. These escape from the body back-to-back and are detected, allowing doctors to follow what happens to the biological tracer molecules and thus learn valuable information about the workings of the body.

What resources about antimatter are available from CERN?

The history of antimatter is covered in this article, by CERN Courier magazine editor Gordon Fraser

AN LINK TO THE ANTIMATTER STORY

A leaflet about antimatter can be ordered from the Press & Publication Office
  

A Web site dedicated to antimatter, and which will feature Web casts of important antimatter events at CERN is here.