CERN1's unique new antimatter factory, the Antiproton Decelerator (AD) has begun delivering antiprotons to experiments. These experiments will study antimatter in depth to determine if there is a difference between it and ordinary matter.
Any difference between antimatter and matter would be extremely interesting since it is not yet understood why the universe is made of matter. Physicists believe that the Big Bang created equal amounts of antimatter and matter, which would then have annihilated, leaving nothing. The great mystery is why there was enough matter left over to from the universe.
CERN is probably best known for enormous accelerators and research using very high energy particle beams. The AD is the antithesis. It is only 188 metres in circumference and is designed to actually decelerate particles rather than accelerate them. It takes high energy antiprotons, groups them together tightly in bunches, slows them down to the leisurely pace - by CERN standards - of a tenth of the speed of light, and delivers them to experiments. At this point, the remarkable technical sophistication of the experiments takes over. The experiments either capture the antiprotons in cages of electromagnetic fields or insert them into ordinary atoms. The velocity of the trapped antiprotons is now reduced to a few millionths of the speed of light. The once unruly antiprotons are virtually at standstill and further study can begin.
Two experiments, ATHENA and ATRAP, aim to add positrons - anti-electrons - to the caged antiprotons to make atoms of antihydrogen. A third, ASACUSA, traps the antiprotons in a cage conveniently provided by nature – the helium atom. The goal of all three is a detailed comparison of matter and antimatter leading to an understanding of why nature has a preference for matter over antimatter.
The first steps at CERN on this path were taken in a series of experiments, between 1982 and 1996, at the Laboratory's LEAR facility, where the techniques for trapping antiprotons were developed. In 1995 the first man-made atoms of antihydrogen were made at LEAR. Those atoms were fast-moving and soon annihilated with matter. However, the experiment demonstrated that anti-atoms could be made, and with the AD the quest begins to make antihydrogen atoms that are slow enough to be trapped, whereupon lasers directed at them can probe for tiny differences between antihydrogen and hydrogen.
The successful start-up of the new AD facility gives the international physics community a new instrument to examine nature and perhaps answer the question, "Why do we live in a matter universe?"
For full information on the AD start-up, read here!
For more information on the individual experiments go to the following pages: