What have we learned from antiproton proton scattering?

Abstract

From recent charge exchange measurements in the extreme forward direction, an independent and precise determination of the pion nucleon coupling constant is possible. This determination has reopened the debate on the value of this fundamental coupling constant of nuclear physics. Precise measurements of charge exchange observables at forward angles below 900 MeV/c would also give a better understanding of the long range part of the two-pion exchange potential. For example, the confirmation of the coherence of the tensor forces from the pion exchange and the isovector two-pion exchange would be very valuable. With the present data first attempts at an $\NbarN$ partial wave analysis have been made where, as in nucleon nucleon scattering, the antinucleon nucleon high J partial waves are mainly given by one-pion exchange. Finally a recent $\pbarp$ atomic cascade calculation and the fraction of P-state annihilation in gas targets is commented on.