CERN1 will build a new experimental facility, the Antiproton Decelerator (AD) by transforming an existing CERN machine the "Antiproton Collector", which produces and stores antiprotons into a "all-in-one" machine which can, in addition, decelerate, cool, and eject antiprotons at low energies (5.8 MeV). The transformation will cost about 7 million Swiss Francs, and will be funded by special contributions from several countries, among which are , Denmark, Germany, Italy, Japan, Poland and the United States.
The main goal of the new facility is to allow a community of about 150 physicists to continue their efforts to work with ultra low energy antiprotons, in particular for the purpose of antihydrogen research. Antihydrogen is an atom made entirely of antiparticles: while ordinary hydrogen consists of a positive proton with a negative electron orbiting around it, the antihydrogen atom has a negative "antiproton" in the centre bound to a positive "positron".
Pioneering experiments at CERN and more recently at Fermilab in the US, had only one aim : to produce and to detect a few antihydrogen atoms. They succeeded in demonstrating that antihydrogen can indeed be produced, but the real goal is more challenging: the precise comparison of the physical properties of matter and antimatter atoms. Three quarters of our universe is hydrogen and much of what we have learned about it has been found by studying ordinary hydrogen. If the behaviour of antihydrogen differed even in the tiniest detail from that of ordinary hydrogen, physicists would have to rethink or abandon many of the established ideas on the symmetry between matter and antimatter.
The answer is in the study of the antihydrogen atom, best done at rest. The techniques needed to capture antimatter in electrical and magnetic bottles or traps, allowing for high precision analysis are under intense development at CERN. Two experimental collaborations, ATHENA and ATRAP have been formed to produce antihydrogen and to study its spectroscopy, once the AD is in operation, as early as Spring 1999. Each experiment envisages the production and capture of more than 1000 antihydrogen atoms per hour. Antihydrogen promises to be a tool of fantastic sensitivity for finding out whether a world made of antimatter would really be indistinguishable from our own. A third pillar of the AD programme will be a Japanese - European project to investigate the recent discovery that particles of the antiworld are sometimes able to survive ten million times longer than was thought possible in what is, for them, a hostile environment - that of our everyday world of matter. A general purpose area will also be set up to accommodate a number of small experiments in rapid succession. Monbusho, the Japanese Ministry of Education, Science, Sports and Culture, has announced that the "Antimatter Science" project has been selected as one of the two most important research projects to be carried out from 1998 and will support Japanese participation in the experiments on the Antiproton Decelerator with funding of approximately 10 million Swiss Francs.
Just over a year after the announcement of the production of the first 9 anti-atoms at CERN (PR 01.96) in January 1995, the approval of the Antiproton Decelerator opens up new exciting research possibilities for scientists from all over the world waiting to increase our knowledge of antimatter. The questions are fundamental : Why, if the same quantities of matter and antimatter were produced during the Big Bang, as is supposed, is our Universe made entirely of matter? Does gravity has the same effect on antimatter as it does on matter? The solutions to these questions could lie in the results which will be produced by the Antiproton Decelerator?