Physics of the antiproton/proton system

Interest in antiproton physics has grown because of the successful experimental program at the CERN LEAR facility. A large volume of data has been collected on the reactions bar pp → bar pp (elastic scattering) and bar pp → bar nn (charge-exchange scattering), including spin-dependent observables. The high quality and variety of data have elevated the antinucleon system to a valuable source of information about the two-body nuclear force. A method of partial-wave analysis has been developed that allows one to extract in a reliable manner the antinucleon-nucleon phase-shift parameters from the database below 925 MeV/c. The complexity of the bar pp system is such that for a single energy one must determine 8 times the number of phase-shift parameters found in low-energy pp scattering. Uncertainties in the phase shifts are discussed. The present results represent sorely needed progress in the field and can be very useful in planning future experiments. The issue of the antinucleon-nucleon resonance spectrum is briefly addressed