The ALPHA experiment is a successor of an earlier antimatter experiment, ATHENA. Set up in late 2005 with similar overall research goals as its predecessor, ALPHA makes, captures and studies atoms of antihydrogen and compares these with hydrogen atoms.
Creating antihydrogen depends on bringing together the two component antiparticles, antiprotons and positrons, in a trapping device for charged particles. Since antihydrogen atoms have no electric charge, once they form they can't be confined in such a device. In the ATHENA experiment the antiatoms would drift naturally to the walls of the trap. Because these walls were made of ordinary matter, the contact caused the antiatoms to annihilate a few microseconds after they were created.
ALPHA is picking up from where ATHENA left off. ALPHA uses a different trapping method to hold the antihydrogen atoms, and will keep them for a longer period before they annihilate with ordinary atoms.
In June 2011, ALPHA reported that it had succeeded in trapping antimatter atoms for over 16 minutes: long enough to begin to study their properties in detail. This should give the physicists time to take measurements and to find more answers to the antimatter mystery.