The ATRAP Collaboration announces the first use of cold positrons to cool another type of particle -- antiprotons in this case.  ATRAP now has both of the ingredients of cold antihydrogen in the same trap structure at the same time -- both 4.2 K antiprotons and 4.2 K positrons -- and they are interacting.  This is the closest that anyone has been to producing cold antihydrogen -- the entirely antimatter atom in which a positron orbits an antiproton.  It seems very likely that antihydrogen is made during this positron-cooling of antiprotons because the antiprotons and positron are interacting while traveling at a low relative velocity.  The challenge is to observe the cold antihydrogen in a unambiguous way.

CERN's unique new antimatter factory, the Antiproton Decelerator (or AD for short) first delivered antiprotons to experiments in July - November of 2000.  . Antiprotons are the antimatter counterparts of the ordinary protons that make up much of the mass of everything that we see.

For many years CERN has facilitated and encouraged the smallest, lowest energy antimatter experiments as well as the largest, highest energy antimatter experiments for which CERN is famous. In the past, its antimatter factory uniquely produced the lowest energy antiprotons available at any particle physics facility in the world. CERN's TRAP Collaboration developed techniques to reduce the energy of these antiprotons by another factor of 10,000,000,000, so their temperature was only 4 degrees above absolute zero. The antiprotons were captured in tiny traps, containers without walls, that use magnets and voltages to keep the antimatter particles from encountering any ordinary matter. A collision between a matter proton and an antimatter antiproton would cause both to cease to exist - they annihilate.

Continuing in the CERN tradition of supporting important and fundamental antimatter experiments large and small, CERN's new antimatter facility is dedicated entirely to the lowest energy antimatter particles. The new AD, begun in 1997, is actually optimized to slow antiprotons rather than to let them coast or speed up in the manner the other storage rings in the world. Based upon TRAP's demonstration that antiprotons could be accumulated in tiny ion trap much more inexpensively than in a large storage rings, CERN was able to open the way to the new, low energy frontier, and at the same time save resources by replacing three storage rings with the new AD.

Two experiments, ATRAP (the offspring of TRAP) and ATHENA, seek to make cold antiprotons interact with cold positrons (the antimatter counterpart of electrons) in a way intended to form cold antihydrogen atoms for the first time. A third experiment, ASACUSA, creates and studies exotic helium atoms in which an electron is replaced with an antiproton. With the first AD antiprotons, ATRAP has already trapped and electron-cooled antiprotons, and ASACUSA has begun its spectroscopy of exotic helium.

An antihydrogen atom, a positron orbiting an antiproton, is the simplest atom formed entirely of antimatter. Several very rapidly moving antihydrogen atoms were first observed at CERN in 1995, demonstrating that these atoms can be formed. With CERN's new dedicated facility the quest begins to make antihydrogen atoms that are cold enough to be trapped, whereupon lasers directed at them can probe for tiny differences between antihydrogen and hydrogen.

Any difference between antimatter and matter would be extremely interesting since we do not yet understand why we have a universe made of matter. We would expect that the big bang that originated our universe would create equal amounts of antimatter and matter, which would then annihilate, leaving nothing. The great mystery is why enough matter was left over that we and our matter universe could exist.