Antinucleon-nucleon interaction at low energy: scattering and protonium

We present nucleon-anti nucleon scattering experiments performed at the Low Energy Antiproton Ring (LEAR) of CERN. The data are reviewed and the underlying physics is discussed, in particular by comparison with the predictions of current models based on meson exchange and short-range absorption. A detailed description is given of protonium, which gives information on the interaction at zero energy and is the initial state when annihilation occurs at rest. (C) 2002 Elsevier Science B.V. All rights reserved.