Mixing antimatter and matter usually has predictably violent consequences – the two annihilate one another in a fierce burst of energy. But physicists at CERN in Geneva have found a new way to make the two combine, at least briefly, into a single substance. This exceptionally unstable stuff, made of protons and antiprotons, is called protonium. The researchers believe that some of the antiprotons reacted with ionised molecules of ordinary hydrogen, stealing away a proton. These proton-antiproton systems lasted microseconds at most, but that was long enough to drift away from the core of the experiment before exploding. Protonium has been made before, but only in violent particle collisions. The new chemical method could be used to make it in much larger quantities.
Source: Physical Review Letters, vol. 97, no. 153401 (2006): Evidence For The Production Of Slow Antiprotonic Hydrogen In Vacuum
Abstract