Antihydrogen Revealed

18 September 2002

Physicists working at the Antiproton Decelerator (AD) facility at CERN, the European laboratory for particle physics, have announced* the first controlled production of large numbers of antihydrogen atoms at low energies. After mixing cold clouds of trapped positrons and antiprotons - the antiparticles of the familiar electron and proton - under closely monitored conditions, the ATHENA collaboration has identified antihydrogen atoms, formed when positrons bind together with antiprotons. Central to ATHENA's observations is the antihydrogen annihilation detector, which surrounds the trap where the antiprotons and positrons are mixed. When a positron and an antiproton bind together to form a neutral antihydrogen atom, it escapes the trapping electromagnetic fields, which are set up by metal electrodes. The anti-atom then strikes one of the electrodes, and the positron and antiproton annihilate simultaneously in the surface of the metal.

In this image, the positron has annihilated with an electron to create two back-to-back gamma rays - shown here as the red line joining lower left and upper right - which are detected in a layer of caesium-iodide crystals (red squares). The antiproton has annihilated with a proton to create charged particles (pions) - in this case four of them - which are detected in two layers of silicon-strip detectors (the long pink blocks) and in the crystals (yellow squares).

For further information see the CERN Press Release

Credit: ATHENA collaboration