.Physics Letters B 455 1999 311–315 The ingredients of cold antihydrogen: Simultaneous confinement of antiprotons and positrons at 4 K

Low energy antiprotons and cold positrons are stored together and observed to interact for the first time. The particles and the nested Penning trap that confines them are cooled to 4.2 K, within a vacuum better than 5=10y17 Torr. The simultaneous confinement clearly demonstrates the potential of a nested Penning trap for the production of cold antihydrogen. Contaminant ions play a deleterious role, and we observe a surprising coupling between the positron an