Two-body reactions involving antiparticles

The role of two-body reactions involving antiparticles in identifying the relevant degrees of freedom (baryons and mesons versus quarks and gluons) in low-energy strong interactions is discussed. A combined study of the K + N and K-N system (K- being the antiparticle of the K+) provides information about the relevant mechanisms building up the short range hadronic repulsion. On the other hand, in the antinucleon-nucleon (N-bar N)sector, reliable conclusions cannot yet be drawn, mainly because of the complicated dynamics in the annihilation part. For hyperon production processes the dominant role of two-step reaction, e.g. p-bar p→ Λ-bar Λ → Σ-bar Σ is pointed out and suitable observables (not measured so far) are identified which should be able to discriminate between various transition scenarios. (author)